This article appeared in the Spring, Summer and Winter 1998 issues of The Maine Organic Farmer & Gardener.
By Jean English
Twelve years ago, my husband and I planted our first Christmas trees. We planted the last of the first on May 6, a date I remember because on the next day, May 7, our daughter was born. As you can imagine, I didn’t do any of the actual planting, just plodded along and kept my husband company.
In 1995, we started selling those trees, making a couple of hundred dollars that first year and a few hundred the next. This past Christmas, we sold 47 trees at $15 each – making enough money ($705) to offset much of our Christmas spending. Next year we hope to sell 100, and within a couple of years after that we hope to be selling 200 each year and bringing in about $3,000 each December. Those of you who grow fresh vegetables or other warm-season crops might be interested in generating such additional income in the off season.
While the income from Christmas trees comes during the off season, much of the work involved in growing them does not. They need to be planted in late April and early May and are best pruned in late June and through July. So, if you are growing vegetables, flowers or other summer crops, you need to allow a couple of hours per day during these times for planting and pruning Christmas trees – or you can contract out those jobs. These are excellent jobs for teenagers.
In addition to generating income, Christmas trees are a pleasure to grow. The time I spend in the plantation pruning is some of the most peaceful, quiet time that I get in the summer. Several species of birds have taken up residence in our trees and in the grasses that grow between the trees – one of the many benefits of growing trees organically. The abandoned field in which we are growing trees is improving every year, because hay is no longer being taken off of it three times a year with no nutrients being added back to the soil. It’s being maintained as an agricultural area, too, because invading woody plants are removed. The plantation provides a place of scenic beauty, a place for picnics in spring, summer and fall, a place for wildlife, a place where neighbors race their snowmobiles. Because we sell on a cut-your-own basis, we get to see many of our friends and neighbors when they come for trees. Like selling produce at a farmers’ market, selling Christmas trees can be a social event.
If you think you can find the time to plant, prune and sell Christmas trees, and if you have the patience to wait about 10 years for a plantation to generate income, this might be a good crop to add to your farming system.
Selecting a Site
Christmas trees grow best on a gentle north slope that has no frost pockets and is protected from prevailing winds. Don’t plant in gullies, ditches or other low-lying spots that are susceptible to frost. Southern slopes tend to have less moisture in the soil, and trees start growing sooner in the spring on them; that new growth is susceptible to late spring frosts, which can kill the growing tips of branches and deform the trees. Excessively dry or wet sites are undesirable, so avoid both sandy soils that are low in organic matter and heavy clay soils. The soil should be deep enough to allow for good root development and moisture retention. If security is a problem in your area, you might want to plant your trees away from the road and close to your house. Ours are close to the road and away from our house …
The existing vegetation can indicate whether the site is suitable or not. If evergreens are beginning to grow in a field on their own, the site will probably support cultivated evergreens. If the site is abundant in alders, sphagnum mosses and blueberries, maybe you should grow blueberries.
If trees are volunteering in your field, you might decide to simply go along with nature and start mowing around those trees, pruning them, and removing competing woody plants. That’s one way to start a plantation or to get some early trees while waiting for plantation-grown trees to mature, but because self-sown trees rarely grow in rows, they can be difficult to manage.
Preparing the Ground for Planting
Recommendations for growing Christmas trees are almost all based on a chemical approach – chemical fertilizers, herbicides, insecticides, fungicides and miticides. It has always struck me as a great inconsistency to grow a plant that symbolizes life by applying poisons to that crop. It is difficult to extrapolate from these recommendations to organic culture, and in fact the plethora of chemicals recommended – especially the herbicides – can dissuade a potential grower from trying organic methods.
I was lucky when we first came to Lincolnville to interview a local grower, Ralph Hunt, who told me, “I don’t use any herbicides, insecticides or suicides!” Actually, he later told me that he used a little herbicide around his trees the year he planted them, but encouraged me on my idea of using a mulch of roofing paper around the trees as an alternative. I knew that Ralph and his wife made enough money from his trees and wreaths to pack up the day after Christmas and spend the rest of the winter in Florida, so I felt confident that I could grow my trees without chemicals, too.
Our 3-acre plantation is in a field that was cut for hay a few times each summer for at least a decade. No lime or fertilizer was ever added. To prepare for planting, my husband mowed the field and turned over a 1-foot-diameter circle of sod at each perspective planting site in early summer – just after bug season; he stomped the inverted section of sod back into place and let the sod rot until the following spring. He would like to have done this job earlier in the spring to give the sod a longer period for decomposition, but didn’t care to battle the blackflies.
Some publications say that when planting in old pastures or hay land, you can turn the soil with a disk harrow, or plow the rows where the trees are to be planted. This should be done several months before planting so that the soil has time to settle and eliminate air pockets, which might otherwise kill transplants. (Publications that recommend herbicides suggest that a circle 2 feet or larger in diameter be prepared, or that a strip of soil about 3 feet wide all along the planting row be treated with herbicide.) Publications from Cooperative Extension suggest that such a field, before planting, could also be plowed, harrowed, limed and fertilized according to soil test recommendations. (Lime usually isn’t necessary unless the pH is below 5.5, although a pH of 6.0 can benefit balsam firs. If you add lime, be sure other nutrients are adequate and still in balance, otherwise needles may turn yellow.) Other Extension publications say that fertilizer is most economically applied on a per-tree basis. Still others recommend applying bands of herbicide where the trees are to be planted and mowing the grass in between.
Is there an organic alternative to using herbicides before planting trees? I’ve considered using junk mail catalogs to kill the sod the year before planting. Newspapers covered with a mulch, such as wood shavings or manure, might also work. Sod can also be removed with scalpers mounted on planting machines at the time of planting.
Scheduling and Spacing
We planted 1 acre that first year, another the second and a third the third year. The different planting dates combined with the different growth rates of individual trees has resulted in a field of trees of varying ages so that a continuous supply of trees will be available over the years. When trees are harvested, we replant in those spots the following spring.
Our initial spacing was 5-foot by 5-foot – which, we now believe, is too close. By the time the trees were six or seven years old, it was difficult to get between them to prune and impossible to mow between them. Publications recommend this as a minimum spacing, say that it takes 1740 trees to plant an acre at this spacing, then say that anything more than 1,000 trees per acre is excessive! Other spacings that are recommended are 5×6 (1410 trees per acre), 6×6 (1210 trees per acre), 6×7 and 6×8. At this point, I would recommend setting the trees 5 to 6 feet apart within rows and setting the rows 7 feet apart. This will give you enough room to prune, even when the trees are larger; will enable more light to hit each tree, making a fuller specimen; and will enable you to cut the grass between the rows with a tractor-mounted bush-hog, at least for the first five or so years of growth; and will enable more air to circulate, cutting down on diseases.
When you lay out your planting, leave room for access roads. One publication says that no tree should be more than 50 feet from an access road; another says 200 feet. Two hundred feet should be a maximum: These trees are pretty tough to drag out of the plantation when they’re 6 or 7 feet tall, weighed down with ice and/or snow, and you have to walk through a foot or two of snow. Access roads can also be important in case of fire. These roadways should be 12 feet wide to begin with, because by the time the trees grow in, that distance will be reduced to 7 or 8 feet.
Assuming you’ll be mowing the grass in your plantation with a tractor-mounted implement, be sure to leave enough room at the ends of each row to turn the tractor around.
We set out both balsam fir and Scotch pine in our first year of planting. We knew balsams were a favorite of New Englanders (and of us), and all of the extension publications we read said to include Scotch pines because they grew fast and would shorten the wait for some income.
While some growers do make money with Scotch pines – selling them out of state or to large retailers such as Wal-Mart, I believe – I would not recommend them for local, cut- your-own markets. During the three years that we have been selling trees, only two people have specifically said they wanted a Scotch pine. The needles of this tree are very sharp – they are awful to prune – and the tree doesn’t have the fragrance of balsam. Our Scotch pine plantation got away from us, too, when I was pregnant and when my son was an infant, because I wasn’t able to get to the pruning then. Balsams are more forgiving of such neglect; Scotch pines aren’t. So now our 500-tree Scotch pine plantation is a bird sanctuary, picnic area, and tree-climbing area. One day last winter, my daughter traveled from the top of one tree to another and another, traversing 11 trees without stepping on the ground.
Last year we planted 100 Concolor firs where balsams had been harvested because a few people in our area are starting to recognize and ask for this tree. We also have a few white pines that volunteered in the plantation, and I have some Eastern red cedar seedlings that will be ready to set out in a couple of years. The latter is a popular tree in the mid-South. Ever since I saw a smallish (about 3-feet-high) one sitting on a table in Kentucky, its dense greenery decorated with lace and delicate ornaments, I’ve wanted to grow these as Christmas trees (and landscape ornamentals).
The following list describes some of the other species that are grown as Christmas trees. I strongly recommend that you start with balsam firs.
Obtaining Planting Stock
The way in which my husband obtained most of our planting stock violated my most basic horticultural instinct: to do everything you can to protect plant roots. However, when Dennis was growing up in Ohio, he worked at a Christmas tree farm, so I had to trust him when he said you could simply pull – yes, literally pull – balsam fir seedlings from their native stands in April, as soon as the frost had left the ground. He would go to an open spot in the woods, grab a 6- to 12-inch-tall seedling, yank it from the ground, and put it in a sheetrock bucket of damp peat moss. After he had a hundred or so, he’d set them out in the plantation. “Ninety-five percent of them survived,” he’d remind me later.
I have since read that this is a viable way to get Christmas tree seedlings just as the frost is leaving the soil, since the soil is saturated with water then and the seedlings lift very easily. This can be done even when frost is still in the soil at a depth of 6 inches or more. Publications suggest going to a spot where the seedlings are growing in the open, such as a recently logged or bulldozed area, and pulling up the native, 3- to 8-inch-tall seedlings while they’re dormant in the spring, packing them in wet peat moss, rolling them in sacking, and setting them in a transplant bed, taking care to keep the roots moist at all times. After two years in the transplant bed – at a density of 30 to 50 plants per square foot – the firs are transplanted to the field. Most publications recommend against direct planting from native stands to the field, but it worked for us. The advantages of obtaining trees this way are that they’re free and you know they’re adapted to your local area. If you are collecting from land that you don’t own, be sure to get permission first.
You can also collect seeds and start your own plants in a seedling bed, grow them there for two years, then move them to a transplant bed, where they’ll grow for two more years before heading for the plantation. The advantage of this method is that you can select, to some extent, seed from desirable trees. Since tree color is highly heritable, you can try to establish your own collection of deep green seedlings. Be forewarned, though, that trees of the same species within about 400 feet of one another can cross pollinate; cross pollination can prevent the progeny from resembling the female parent. Seeds should be collected from late August to early October. Keep an eye on the trees where you intend to collect. When the cone scales are beginning to separate, it’s time to collect.
We thought this would be a fun project, but when we headed into the woods, we soon realized that cones aren’t produced until the trees are several years old – and several feet tall. Then they’re produced at the tops of trees. Good old Dennis (who was younger then) climbed those trees for me, got all sappy, but also got the goods. We did start some seeds in a seedling bed and even ended up with about a dozen trees in the plantation to show for these efforts, but we have not pursued this delightful approach since. Having two kids and nonfarm jobs has limited the time for such escapades.
If you want to collect seeds, try to find a place that has been logged and collect them from felled trees. It will be much easier on your heart and less sticky on your hands. Put the collected cones in a paper bag for a week or two and keep them in a warm, dry place. Meanwhile, prepare a seed bed – in the garden, ideally, so that you can keep a good eye on it – by turning over the soil, removing weeds thoroughly, adding peat moss and some forest soil from beneath the type of tree you intend to grow, and whatever nutrients are recommended by a soil test. Well-rotted manure or compost can supply needed nutrients; phosphorus may be added now if necessary, too. Thoroughly water the soil. The ideal seedbed will be well drained, well prepared and weed free. Growing a green manure crop the previous summer and turning it under a couple of weeks before sowing tree seeds is quite helpful.
To extract the seeds from the cones, give the cones enough heat to make them open. Set the bags on a greenhouse bench, for instance, or on a sunny windowsill. After the cones open, shake the bag to free the seeds from the cones. The seeds will have wings on them. You can remove the wings (“dewing” the seeds) by rubbing them while they’re in a burlap sack, then winnowing them. Balsam fir seeds, however, are easily damaged by dewinging, so should be planted whole.
Plant the seeds, 1 or 2 inches apart, before the soil freezes but late enough so that they won’t germinate that fall. Late October is a good time to do this in Maine. After sowing them, cover them with about 1/4 inch of sterile sand or a mix of sand and peat moss and press them into the soil with a board. Cover them with a mulch of fir boughs that is several inches deep. Just after the seedlings emerge in the spring, expose them to 50% light by covering the bed with wood lath screening or snow fencing or by making a grid with stakes and rope about 1 foot off the ground and setting fir boughs on this grid. Leave the shade on until late September. This is especially important for balsam firs. Watch your beds carefully during the spring and summer for damping-off, a fungal disease that clogs the vascular system of seedlings and makes the plants keel over and die. Incorporating peat moss into the soil helps deter damping off by acidifying the soil, and mulching with milled sphagnum moss can help, also.
Remove weeds from the beds as soon as they appear. Small weeds can be pulled, but larger ones can be cut so that tree seedlings aren’t uprooted when the weeds are removed.
Water the seedbed several times a week the first two months after germination if it doesn’t rain; after this water thoroughly once a week if rain doesn’t do the job. Apply a fine mist of water to avoid washing the soil away from the tree roots, and apply at least 1/2 inch each time you water so that the moisture gets deep enough in the soil to reach the roots.
In the fall (around Thanksgiving), mulch the seedlings with straw, pine needles or fir boughs to a depth of 3 or 4 inches. Don’t mulch too early (or leave mulches on too late in the spring) or you’ll promote diseases. In the spring, remove mulches when night temperatures are consistently above 30 degrees.
The seedlings will need nitrogen and phosphorus (unless the soil is already well supplied with these nutrients) while they are growing.
After two years in the seedling bed, move the plants to a transplant bed, where they can be grown about 2 inches apart or at a density of 30 to 50 trees per square foot for two more years. They will not need shade in the transplant bed but may need to be watered and fertilized periodically. Your goal is to produce a compact root system with many fine rootlets rather than a coarse, heavy root system. The tops should have good caliper (stem diameter) and good bud development. Transplant your seedlings to the field when they are 6 to 10 inches tall and have developed good roots and shoots. Transplanting is done, ideally, on a cloudy, windless day. As you dig the transplants from the bed, set them in a bucket of moist peat moss. Remove them one at a time to plant them so that the roots never dry out.
For an excellent discussion about collecting balsam fir seeds and growing seedlings, see “Balsam Fir Seed Collection and Storage,” by M.L. McCormack.
The quickest and easiest – but most expensive – way to start your plantation is to buy seedlings or transplants from a nursery. We in Maine are fortunate to have Western Maine Nursery as a resource. You can buy 2-0 or 3-0 seedlings from Western Maine – that is, plants that grew for two or three years, respectively, in the beds where they germinated; or 2-1 or 2-2 transplants – that is, plants that spent two years in the seedling bed and then one or two years, respectively, in a transplant bed. Transplants will be larger, have more roots and more vigor and a higher survival rate, and will require less time in your plantation before they’re salable. On the other hand, they’re more expensive than seedlings. If you want to save some money but still buy plants, you could buy 2-0 seedlings and grow them in your own transplant bed for a year or two. The species you intend to plant makes a difference, too. Pines usually do well when planted out as seedlings, but short-needled species usually do better as transplant stock.
Your trees should be transplanted to the plantation in the early spring, before the buds swell and after the frost has left the ground. This is around the last two weeks of April and the first week of May in our area. Although August planting is sometimes recommended, our summers have been so dry lately that I would not take the risk of planting then. Frost heaving can be worse with August-planted trees, too.
Using a spade or post-hole auger, one person can plant 600 to 800 trees per day. Tractor- drawn planting machines make the work go faster.
The trees should be set as deep as they were in the nursery, and the soil should be firmed around their roots after they’re planted to eliminate air spaces. Be sure that the roots are well distributed when the trees are set in the ground, because they will tend to remain in their initial position for several years. Trees with roots curving up in a U-shape, for instance, will grow poorly. It is better to cut the ends of long roots than to have them double up. Alternatively, you can push the transplant much deeper into a hole than the desired planting depth, then pull it back up so that it is set at or slightly deeper than the root collar. This will help straighten the roots. The soil is moist enough (usually quite wet) in the spring that you don’t have to water your transplants in. It’s a good idea, however, to transplant on a cloudy, still day, if possible.
Grasses and other plants have well developed root systems that can compete strongly with small trees, especially during the first three years in the plantation, by using most of the available soil moisture, competing for nutrients, and shading Christmas tree seedlings. Some grasses can reduce tree growth by as much as two-thirds. Grasses and weeds can also fuel fires and provide cover for mice, rabbits and other small animals that can damage young trees.
We planted our first crop in a mowed field and mulched with 1-square-foot pieces of black roofing paper to keep the grass down. This worked fairly well, although some of the paper squares blew away, and grasses outside of the 1-square-foot area became problematic after a while. It was difficult to get into our trees to mow with the tractor after the first few years, because we’d set the trees just 5 feet apart in all directions. My husband did his best to mow the perimeter of the acre-plot and to keep the roadways mowed, but the grasses and weeds grew up around the trees in the unmowed areas. For a couple of years, vetch and bedstraw, two climbing weeds, were problematic. I spent some time each July pulling these out of the trees. As the trees got older, however, they outcompeted the weeds. Benefits of not mowing between the trees are that goldenrods and other wildflowers were allowed to bloom, providing pollen and nectar for bees; and ground-nesting birds were given a safe home.
We planted trees further apart in subsequent plots and were able to mow between the rows longer, but still, when the trees were five years old or so, mowing became impossible. If you do rely on mowing, you should do it two or three times a year; ideally, weeds should be kept below 6 inches. One publication recommends using a deflection shield so that you can mow close to trees without damaging lower branches. If you plant your trees in check rows, and if you have level soil, you’ll be able to mow in two directions for a couple of years for better weed control. At least plant your trees in straight rows to simplify mowing! The maximum benefit from mowing comes in spring and early summer, when weeds are lush and growing. Competition is less severe during the later part of the summer.
We simply tolerate weeds in areas where we can’t mow (and enjoy the birds, bees and toads), cutting out woody growth with loppers periodically. As the trees get larger, they shade out more weeds, too. Our trees may take a couple of years longer to mature than those that are grown in herbicide-denuded areas, but the wait is worthwhile for us. We don’t have to deal with chemicals that may be proven toxic some day; we don’t have to worry about contaminating our neighbors’ wells; and we don’t have to worry about poisoning wildlife or destroying habitat.
As an alternative to mowing and herbicides, you could try using a mulch of several sheets of newspaper held down with about 4 inches of sawdust, straw, bark chips or wood chips and applied in a 2- to 3-foot-diameter circle around each tree. As the mulch decomposes, more can be added. Supplemental nitrogen (about 5 pounds of poultry manure or 10 pounds of sheep manure per 100 square feet of mulch) may be needed in such a system. Hummert International (4500 Earth City Expressway, Earth City, MO 63045; 800-325-3055) sells synthetic mulching squares that are held down with large “staples” and look like they would do a good job in tree plantations. They cost about 50 cents each. VisPore Tree Mats, likewise, are 3’x3′ weed barriers that are permeable to water and oxygen. They are available from Treessentials Co., Riverview Station, P.O. Box 7087, St. Paul, MN 55107, Tel. (800)248-8239. As another alternative, rolls of black polypropylene “weed barrier” fabric, which lets air and water penetrate but keeps weed growth down, can be used after trees are planted. The initial cost can be high.
According to ATTRA, “rotary hoes are an effective cultivation tool for in-row weed control and soil cultivation. Rotary tree hoes have articulating arms that retract when a sensor touches the tree. Attached to the swinging arms are rotary tines or disks. Several models are available to choose from, including WeedBadger and Green Hoe.”
What about using grazing to keep growth down around Christmas trees? Linda Kappel- Smith wrote in Country Journal: “Sheep and goats will, unfortunately, eat most evergreens with relish and should only be grazed in older stands where the salable portion of the tree is out of reach. Cows…can generally be trusted to avoid [evergreens]. They will trample the little ones, though, and in pushing between the larger trees, they will snap off some twigs and limbs.” Ponies, she says, are apt to do even more tree damage, and damaged trees can take a couple of years to outgrow their broken limbs. She tells of one grower who estimated that her livestock damaged about 2% of her trees each year (or 20% over the average 10-year life of the trees). The grower doesn’t put livestock in with her trees until the trees are 5 feet tall or more. Despite the losses, she believes grazing her plantation is worthwhile, because she has never had to mow between the trees, and she gets milk and beef from the animals.
I spoke with a grower from Vermont several years ago who was using sheep to keep the vegetation down in his plantation, and he was very happy with the system. He said that as long as he moved the sheep frequently, they ate the grasses and other weeds – their preferred foods – and left the trees alone. One of their favorite foods is vetch – the bane of many Christmas tree growers and target of many herbicide applications.
A publication from the University of Kentucky suggests watching livestock carefully during fly season, when they may rub against trees, and when trees are putting on new growth and animals may be tempted by the succulence. A small flock of sheep in a UK planting during the fall and winter did not browse on the trees.
The Northwest Coalition for Alternatives to Pesticides (NCAP) says, “Many growers in Cape Town, British Columbia, claim that sheep are probably the most commonly used animals for this practice, but cows and even ostriches are also effective.” NCAP also says that cultivating and heat steaming machines can be used for weed control but that the startup costs and management requirements are greater for these than for other methods. According to ATTRA, “steam weeding is an old practice that has resurfaced as a viable technology with recent equipment developments (brand names include Waipuna and Aqua Heat). The Aqua Heat system has performed especially well in orchards, vineyards, and tree farms. Unfortunately, the equipment may be cost prohibitive to the small-scale grower; consequently, these growers may have to build their own hot water devices. Contact Aqua Heat, 8030 Main St., Fridley, MN 55432, Tel. (612)785-2661.” In the Sept.-Nov. 1997 MOF&G (p. 44-45), we ran a short article about Stephen Breyer’s low-cost, homemade, boiling water weeder and his success using it on nursery crops at Tripple Brook Farm in Southampton, Massachusetts.
We have not used any fertilizer on our trees yet. Our soil was very high in phosphorus to begin with and still is (probably the result of annual fertilizing with “complete” fertilizers in decades past, when the land was in continuous corn), and the pH of 5.5 was okay for growing Christmas trees. (Raising the pH to 6.0 would be better for our balsam firs and may help retain more needles.) You should get a soil test before planting your trees and, if the pH and phosphorus need to be adjusted, do so then.
The usefulness of fertilizers in the first year is debated among growers, and Scotch pines, which grow well on soils of low fertility, rarely need fertilizers. Vegetation killed by an herbicide can release enough nutrients for Christmas trees in their first year, and I expect mulching would do the same (if the mulch is not highly carbonaceous and will not, therefore, tie up nitrogen). Granger et al. suggest experimenting with first-year fertilization, since a lack of response to fertilization could result from poor control of competing vegetation; from placing fertilizer too close to newly planted seedlings and consequently raising the concentration of salts in the root zone excessively; or from putting the fertilizer so far from the seedling that the roots can’t absorb it.
After the transplant year, in non-organic systems, about 1/4 pound (a couple of hands full) of a balanced chemical fertilizer is scattered under the branches of each tree each year or two to encourage faster, denser growth with more bud set, more internodal branching and longer needles; to improve tree color; and, possibly, to improve needle retention. A spade full of compost or well rotted manure could substitute for this chemical fertilizer; or you could save your family’s urine all winter and use that on some of your trees! Grazing sheep on your Christmas tree land is another way to cycle nutrients organically and keep weeds down at the same time. See the discussion on grazing under weed control. Likewise, establishing a leguminous crop before planting the trees and then mowing or grazing that crop after the trees are planted would probably fix and cycle enough nitrogen to feed the Christmas trees.
Supplying enough nitrogen is, I think, one area in which we have been too lax with our own trees. Granger et al. say that in the Northeast, nitrogen is the element most commonly required for optimal Christmas tree growth. You have to be careful with fertilizers, though, because if you add nitrogen and don’t suppress the growth of competing vegetation somehow, that vegetation will take up much of the nitrogen and compete even more with your Christmas trees. Also, if you’re adding nitrogen, you want to be sure you supply (or your soil supplies) enough potassium to enable the plant to use that nitrogen. If you need to apply potassium and raise the pH, wood ashes would be a good material to use (but use them carefully because a little goes a long way).
Here are general recommendations regarding chemical fertilizers and lime that might be helpful in thinking about when particular nutrients are needed by Christmas trees:
• A pH of 6.0 can be especially beneficial for balsam firs;
• If you add lime to raise the pH, you may have to add a complete fertilizer or the needles may turn yellow – follow soil test recommendations;
• Apply a high-phosphorus starter fertilizer the year after planting;
• Two to three years after planting, apply a balanced fertilizer every year or as needed:
Tree Size Fertilizer Type Rate
1 to 3′ high P&K, low N 2 to 3 oz./tree (1 Tbsp.)
4′ balanced N,P,K 3 to 4 oz./tree (handful)
6 to 8′ high N, low P,K 6 to 8 oz./tree (1 cup)
Or, as a general rule, provide 1 ounce of fertilizer per foot of tree height. Granger et al. recommend 20 to 50 pounds of actual nitrogen per acre during the first through fourth years after planting and 50 to 100 pounds when the trees have been in the field for five or six years. This should be applied in mid-May or early June. The usefulness of supplying phosphorus after the first few years of growth is debatable, since that element is so immobile in soils. If you do apply chemical fertilizers or urine, distribute them evenly around the base of each tree in a donut shape, from 8 inches out from the base of the tree and extending somewhat beyond the outermost branches.
An extra shot of nitrogen (20 to 30 pounds per acre) in late summer or early fall of the harvest year is recommended to give the trees a good green color when they’ll be sold.
The best discussion I have seen about the nutrition of Christmas trees is Granger et al., “Christmas Tree Fertilization.” (See bibliography.) Their summary recommendations are as follows: “Your fertilizer program should begin with a soil test a year or two before planting. Add the nutrients recommended by the test to the soil and incorporate them. This is particularly important in the case of lime and phosphorus. Sow a cover crop and let it become established prior to planting any trees.
“Add no fertilizer the year of planting, but do implement an effective weed control program. Fertilize trees individually the second year (by hand) by distributing about one ounce of balanced fertilizer (10-10-10, 15-15-15) in a 16-inch-diameter circle around each tree. After two years, either manual or mechanical methods of fertilizer application should be satisfactory.
“Use soil and foliage tests to refine fertilizer applications after the second growing season. Where nutrients are in satisfactory balance, many growers get good results by applying balanced ratio fertilizers such as 10-10-10 or 23-12-18. Balanced ratio fertilizers which utilize ureaform as one nitrogen source (such as 18-11-17) also work well. Where magnesium is deficient, blends such as 10-18-12-3.6 (3.6 percent Mg) are useful.”
I cite these recommendations not to encourage you to use chemical fertilizers, but to encourage you to add any needed lime and phosphorus before planting, and to give you a guide as to when trees need which nutrients.
“Shearing and shaping is the most important activity of Christmas tree farming because the results of the time and labor will determine the marketability of the trees.” So says a North Carolina extension publication, and this is where we have put most of our time.
Pruning creates a denser tree by stimulating internodal buds to sprout and grow (spruces and firs, but not pines, can produce internodal buds between the annual whorls of branches), promoting the growth of existing branches, and maintaining a desirable shape. Pines are pruned from the time they are 2 to 3 feet tall (about two years after they are planted out), while spruces and firs can usually wait until they are about 4 feet tall. Once you start pruning, you need to prune pines every year. You may miss a year with firs, but your trees will look better if you don’t.
Most growers use a machete to shear their trees. This is quick and efficient but results in a tree that is “too perfect,” in my opinion. People who are buying real Christmas trees want them to look like real trees, with the branches reaching out to slightly different lengths in the cone-shaped tree and with occasional spaces in the tree where their ornaments will show up. “Fritz Hier, Cornish Flat tree grower, says many Christmas tree buyers resist the dense, carefully shorn tree that is typically priced at the top of the market,” reported N.H. agriculture commissioner Steve Taylor in 1993 in the N.H. Department of Agriculture Weekly Market Bulletin. “They find these trees are hard to hang ornaments or place presents on.” “These people want a tree they can see through, one that will let ornaments dangle freely,” Fritz told Taylor.
This is one reason why I use long-handled pruning shears to shape my trees, rather than a machete. There are two other reasons. First, I think the shears are more ergonomic, because you use both arms to the same extent to do the pruning. With a machete, you are swinging one arm up and down for hours, which is hard on that arm and hard on your back.
Second, I don’t like machetes because they’re dangerous. If you are right handed, you are supposed to wear a chap on your right leg (and preferably on your left leg, too) to prevent shearing that leg when your right hand sweeps the machete down along the tree again and again. (Wear the chap on your left leg if you’re left handed.) Kevlar gloves are also worn by some workers. The smallest chap I could find was still too large and stiff for me. Since I disturb a nest of wasps or hornets about once a year in our tree plantation, I like to be able to run fast when necessary. With the machete in my hand and the stiff, poorly fitting chap on my leg, I felt quite vulnerable. Hence, the shears. Lots of people are very happy using machetes, though. See if you can borrow one (You’re welcome to mine!) to find out if it suits you.
During the first year or two of pruning, you can actually get away with hand-held clippers, because you’re just cutting the central leader and a small number of lateral branches. During the last year or two of pruning, you’ll probably have to invest in a pole pruner to reach the top laterals and the central leader. These cost about $45 at Agway, but I was lucky to find one for about $20 at Reny’s one summer. (Gloat!)
Spruces and firs can be pruned any time when they are not actively growing, but new bud development will be stimulated best if they are sheared in late June and into July, when the new growth is beginning to firm. Supposedly, balsams can also be sheared during their active, succulent growth period just before late June. When I’ve tried this, though, they continued to grow after I sheared them, and I ended up having to go through the plantation a second time to shorten leaders that had grown too long. You should not shear in subzero weather, because twig dieback will occur on cut branches.
Pines need to be sheared when they are actively growing and when the new needle growth is one-half to two-thirds the length of the mature needles – about June 10 to July 10 in much of Maine. A good schedule is to start pruning Scotch pines by July 1, move on to spruces, then do firs, finishing the job by early August.
Four types of pruning cuts are made: basal pruning; central leader pruning; lateral branch pruning; and corrective pruning.
Basal pruning is removing the lower branches of the tree up to the first perfect whorl. This provides a good trunk area for cutting; a good handle for hauling the tree out of the plantation and putting it in a Christmas tree stand; it reduces the growth of the terminal leader a year or two after it’s done, helping produce a more compact tree; it encourages internodal branching and a denser tree as the tree “tries to replace” lost foliage by increasing the density of the remaining branches; and it makes the tree symmetrical. This is usually done just in the first year of shearing, when the tree is about waist-high.
The central leader – the top, vertically growing “stem” of the tree, the place where the angel or star will sit – is cut back to 8 to 10 inches in order to make a well-shaped, dense tree with a uniform spacing between whorls. This cut should be made at a 45- to 60- degree angle and should be about 1 inch above a good bud; that bud will become next year’s central leader. A right angle or flat cut often results in production of several leaders the following year. When trees have more than one central leader, choose the healthiest looking one and remove the others where they join the main stem. (This is best done with hand clippers.) Leaving more than one leader will create a multi- stemmed tree. Start pruning the central leaders when the trees are waist-high – at the same time you do basal pruning.
The tips of the lateral branches are cut to increase the density and control the shape of the tree. To do this, picture a cone around the tree and cut any branches that extend outside of the cone. Usually only the terminal twig of each lateral branch needs to be cut, and you should only cut into the current year’s growth. If you have to cut into second year wood, bud formation will not be so vigorous, but if only a few branches are involved, the tree should recover eventually. When you are done, the base should be about two-thirds as wide as the height of the tree. An 8-foot tree, for example, should have about a 5-foot- diameter base. The lateral branches of the top whorl should be cut to two-thirds the height of the pruned central leader. This prevents these top-most laterals from competing with the central leader and becoming multiple leaders themselves. If the top whorl has too many lateral branches (more than 8 or 10), remove the extras; the remaining ones should be evenly spaced around the trunk.
Finally, correct deformities when you are pruning. On a lopsided tree, for instance, the longest laterals on one side of the tree can be “reigned in” so that the tree is more symmetrical. It may take two or three years to get such a tree back into shape. Some trees should receive the ultimate pruning at this time: complete removal. Get rid of trees that are not growing well due to poor genetics, poor soil, or insect or disease damage any time you see them.
The summer before the trees are to be harvested, shear them very lightly so that they have a natural appearance come December.
Supposedly you can prune 50 to 70 balsam firs an hour, depending on tree height and site conditions; pines can take about twice as long. I spend about 60 hours in late June, July and early August pruning the 2500 trees in our 3-acre field.
The best way to learn how to prune is to read the basics, then go to a couple of pruning demonstrations, read the basics again, then practice on your own trees. The job soon becomes second nature.
If you read the list of problems that can plague Christmas trees, you’d probably never try to grow them. Late spring frosts can kill new growth; dry summers can stunt growth; wet summers can cause foliage to turn yellow; deer can feed on the succulent green branches while mice and rabbits can gnaw the trunks; perching birds can break growing tips. In addition, a long list of insects, diseases and mites can attack the trees, and weeds are an ever-present threat.
We have had remarkably few problems with such pests. When late spring frosts have killed a few growing tips, we have just pruned less: frost damage did some of the pruning for us. We have lost some central leaders, but have remedied the damage by corrective pruning: i.e., establishing a new central leader from the next whorl down the trunk. We have had to cull some trees that succumbed to a disease that has sensitive fern as the alternate host; eliminating the fern by mowing or grazing or improving drainage in those areas might help. We have not had any problems with mites, probably because of the diversity of insect life that occurs when trees aren’t sprayed with any insecticides or miticides. Most growers in our area spray Scotch pines for weevils, which can ruin central leaders.
According to NCAP, aphids and spider mites, serious threats to Christmas trees in the Pacific Northwest, are best controlled by beneficial insects. Jack DeAngelis, Oregon State University Extension Entomologist, says, “Stick with generalist insect predators – they have the best chance of finding something to eat in the fields – and start small.” He recommends green lacewings, syrphid flies, and the predatory midge Aphidoletes. The first two are generalist predators on aphids, spider mites, etc., and the last are aphid predators. Predator mites and Asian lady bird beetles can also be encouraged in the Northwest, he adds.
The following information, from “Spider Mites,” Pest Notes (6), Jan. 1995, produced by IPM Education and Publications, UC Statewide IPM Project, University of California, Davis, CA 95616-8620, may be helpful if you have trouble with mites. It was written for orchardists, but some of the information relates to Christmas trees, as well:
“… Purchase and release of predatory mites can be useful to establish populations in large plantings or orchards, but the best results are obtained by creating favorable conditions for naturally occurring predators – for instance, by avoiding dusty conditions and pesticide sprays.
“… A good rule of thumb is that one predator is needed for every 10 spider mites to provide control. More than one application of predatory mites might be required if you want to reduce pest populations rapidly. Concentrate releases in hot spots where spider mite numbers are highest. Once established on perennials, predatory mites can reproduce and provide biological control indefinitely without further augmentation unless nonselective insecticides are applied that kill the predators…
“Cultural practices can have a significant impact on spider mites. Dusty conditions often lead to mite outbreaks. Oil orchard roads or water pathways at regular intervals. Maintain ground covers in orchards and limit traffic, especially in ‘hot spots’ where mites are frequently a problem. Water-stressed plants are less tolerant of spider mite damage. Be sure to provide adequate irrigation. Midseason washing of trees and vines with water might help prevent serious late-season mite infestations.
“In gardens and on small fruit trees, regular and forceful spraying of plants with water will often reduce spider mite numbers adequately. Be sure to get good coverage, especially on the undersides of leaves…” The report also points out that some pesticides actually stimulate spider mite populations. Carbaryl (Sevin), for example, apparently directly cause mites to reproduce faster, and it can further favor spider mites by increasing the level of nitrogen in leaves.
Our main problem has been with yellowing and needle cast in the fall – partly a natural occurrence as second- and third-year needles are shed, but one that could be limited, I think, by better fertility, more water during August, and better control of weeds. Most growers apply fungicides a few times each summer to help reduce this needle cast, which can also be caused by some disease organisms.
Harvesting and Marketing
Christmas trees are ready to harvest when they’re 6 to 8 feet tall. This can be as early as 5 years of age for pines but is usually about 10 or more years for balsam firs. An area that was planted one year usually will take about three years to harvest, since the trees grow at different rates.
If you are going to sell wholesale, take inventory in the summer and line up your buyers then (or sooner). Let buyers know the species, size classes and quality of your trees. You can refer to USDA grade standards for Christmas trees. Fir and spruce should be cut after a killing frost has set the needles, while pines should be cut before a hard frost to prevent foliage discoloration and old needle drop. Once trees are cut, they should be stored in a cool, shaded area that is protected from the wind.
Trees can be cut right to the ground to produce a tree of maximum height and to leave no stumps over which you might trip. In the spring you can replant between the stumps. Alternatively, you can practice “stump culture” – leaving a stump with some live branches on it after harvesting the rest of the tree. A bud or turned up branch is then cultured into a second tree by removing all of the branches except one in June. This is, reportedly, a slow and inefficient process (“Christmas Trees Pay Off…”, Yankee Woodlot series), and it’s better to replant with vigorous transplants.
If you are selling directly to the consumer, have your advertising ready to run just after Thanksgiving. You can run ads in newspapers – using a photo of your family with the trees is a good eye-catcher – on the radio or on signs or posters; send post cards or other direct mail; and/or be included in a state list of producers. As with any direct marketing project, word-of-mouth can be your best advertising tool. Also, you can often get free advertising by letting local newspapers know about your operation. Editors usually are looking for some holiday photo ops in December.
We started selling a few (about 15) trees two years ago just by letting friends know, either in person or by post card, that some trees were ready and by putting a sign at the end of our driveway. We actually did not want to advertise too much because we didn’t have many trees ready that first year. The following year about 30 trees were ready, so we sent a few more postcards. This year we sold 47 trees – all by word-of-mouth from previous customers, postcard notices, the sign at the end of the driveway, and a poster at the local food co-op. We started advertising our trees as certified organic this year; that may have brought a few more customers. I read about one grower who calls artificial trees – the main competitor of natural trees – “toilet-brush trees.” There are many ways to make your trees sound appealing.
We sell our trees on a cut-your-own basis, which is good because we don’t have any cut trees sitting around on Dec. 26th. On the other hand, if you’re going to have the general public traipsing around your land with saws and axes, you’ll have the added expense of liability insurance. This year we paid $100 for a month of insurance.
We started advertising that our operation would be open on weekends only, but people didn’t pay much attention to that. They came when they came. We have gotten used to the idea that most people will come on weekends, but stray customers will be here just when you sit down for lunch on Wednesday or supper on Thursday. We have had a few customers come after dark and happily cut trees that they could barely see, or shine their headlights on the trees until they find the “right” one. This year I think we’ll keep a few cut trees ready by the back door for customers who come late, who come during storms or who don’t want to cut their own.
One of the benefits of selling directly to the customer is that you can also sell wreaths, maple syrup, honey or other products. We have not taken advantage of this benefit yet, but may eventually.
You might consider selling live trees in addition to cut trees, although the market for them may be limited in our rural areas. Table-top trees could be another specialty.
We price our trees at $15 each and leave it up to the customers to get their money’s worth. Some growers price trees by height.
We have expended very little in actual cash to establish our trees because we pulled most of our seedlings from our own land, did all of the planting, pruning and other care ourselves, and use a tractor and bush-hog that we would have bought for the farm anyhow. We are using land that was idle and on which we would have been paying taxes anyhow. We have a crop that, if it doesn’t sell one year, will sell the next. It fits well with raising children in that you can, more so than with vegetables or fresh fruits, let some jobs go while the children need or want you, then catch up on the chores later. We have established a pleasant summer routine in which I write and edit for a couple of hours in the morning, prune trees for an hour or two, then take the kids to the beach. If I get behind on the pruning, I can catch up on the weekends while my husband takes the kids to the beach.
For the past few years, my daughter has helped me prune – just a few trees at first, but more each year. I find that if I don’t ask her to help and just let her do what she wants when she shows up in the trees, she is very helpful and is good company, to boot. If you have children in your life or neighborhood, teaching them how to prune when they ask can give them a valuable skill, make them feel useful, and maybe even encourage them to start their own horticultural enterprise someday.
We are starting to make money on our trees. At $15 per tree, we made two or three hundred dollars each of the first two years of sales, and $705 this past year. Soon I hope to be selling 200 trees per year – a sustainable number for our 3-acre plantation – and making $3000 – a welcome addition to our income at Christmas time. University of Kentucky forester Dr. Deborah Hill estimated that, figuring a 20% loss of a plantation over a seven-year rotation, the plantation should yield about a 14% return on investment. (Other experts cite losses of 25 to 30% due to mortality and culling – even with pesticide use. So far our losses, with no chemical pest controls, have been under 15 percent.)
You might consider intercropping as a means of generating income from your plantation in its early years. Two years of data from Kansas showed that muskmelons could be grown between rows of Scotch pines during their first two years in the field and could bring in considerable income then. When the melons were grown on strips of black plastic mulch, tree height was shortened by a couple of inches over two years; when melons were grown in bare (herbicide-treated) soil, tree height was not affected.
In Alabama, researchers found that Christmas trees could add $176 per acre net profit on cattle grazing land if the trees (Virginia pines) were grown 8 feet apart in rows 33 feet apart (165 trees per acre) and if the trees were protected by a single strand of electric fence on each side of the row. The fencing, incidentally, helped organize a rotational grazing system. The researchers did not recommend adding cattle to existing Christmas tree operations because of the expense of starting a cattle operation.
In Arkansas, field corn has been planted between loblolly pine that was being grown for timber.
Here in Maine, Austin Moore is growing Christmas trees among his apple trees to get some income while he waits for the apples to mature. His Christmas trees – balsam and Fraser firs – are about eight years old now and he just started cutting a few last Christmas. His apple trees – standard size – are planted on 30-foot centers, and he has one row of Christmas trees planted between each row of apple trees, so he has a 15-foot space between the Christmas tree row and the apple tree row. Christmas trees are 6 feet apart within that row. Also, he has two Christmas trees planted between each apple tree in the apple rows. He keeps the grass down by mowing with a riding lawn mower. He hasn’t used any pesticides on his Christmas trees and is happy with the way they’ve grown. It’s like any crop, he says: “If your soil is good, your trees are good.”
At the Dale Bumpers Small Farms Research Center in Booneville, Arkansas, agronomist Robert D. Webster is studying alternative crops to plant in agroforestry plantations. He has planted 41 species of herbs – including ginseng, sage, thyme, St. Johnswort and chamomile – between single rows of five-year-old pine trees to test the economic potential of such crops in an alley cropping situation. Interplanting herbs among Christmas may have potential.
You can generate some added income by managing balsam firs (and other evergreens) for tip production for wreaths. The wreath-making season begins in early November, after cold weather has hardened the needles (after 20 days, beginning in September, during which the temperature has dropped below 40 degrees or after three consecutive nights after Nov. 1 of 20 degrees or colder); by making wreaths in November and selling wreaths and trees in December, you can add two months of production and sales to your farming system.
If you are thinking of growing Christmas trees, I’d suggest starting small – that is, planting 10 acres or less, 2 acres each year for five years. Plan on spending between 90 and 150 hours per acre per year maintaining your plantation – mowing, pruning, replanting and harvesting. This size initial planting will enable you to determine how many trees you can tend, and if the market for real Christmas trees is glutted, you’ll have just enough for your local market and will probably be able to weather that glut better than a large scale grower who relies on Christmas trees and distant, more competitive markets for a greater proportion of his income.
Christmas Tree Prices
from Weekly Market Bulletin, N.H. Dept. of Ag., 12/17/97
* Balsam fir $8 to $19
* Fraser fir $8 to $24
* White pine $10
* White spruce $6 to $10
* Balsam fir $15 to $45
* Douglas fir $25 to $30
* Fraser fir $20 to $55
* Scotch pine $10 to $30
* White pine $10 to $25
Cut Your Own $20 to $30
American Christmas Tree Journal, National Christmas Tree Assoc., 611 E. Well St., Milwaukee, WI 53202; Tel. (414)276-6410. Comes with $125 membership in National Christmas Tree Association.
Anon., “So You Want to Grow Christmas Trees?” Yankee Woodlot Bull 7048, Univ. of Maine Coop. Extn., Orono, ME 04469.
Anon., Balsam Fir Tip Gathering,” Yankee Woodlot Bull. 7011, Univ. of Maine Coop. Extn., Orono, ME 04469.
Anon., “Making Balsam Fir Wreaths,” Yankee Woodlot Bull. 7012, Univ. of Maine Coop. Extn., Orono, ME 04469.
Anon., “Making Wreaths for Profit,” Yankee Woodlot Bull. 7013, Univ. of Maine Coop. Extn., Orono, ME 04469.
ATTRA (Appropriate Technology Transfer for Rural Areas), P.O. Box 3657, Fayetteville, Arkansas 72702; Steve Diver, Technical Specialist; Tel. (501)442-9824; (800)346-9140; fax (501)442-9842; e-mail: [email protected] ATTRA can provide a packet of information about growing Christmas trees.
Bissell, Lewis, “Planting Balsam Fir for Christmas Trees,” Forestry Notes, Feb. 1974, Univ. of Maine Coop. Extn. Service, Orono, ME 04469.
Blumenstock, Bud, “Christmas Tree Marketing,” Yankee Woodlot Bull. 7009, Univ. of Maine Coop. Extn., Orono, ME 04469.
Blumenstock, Bud, “Christmas Trees Pay Off, If You Can Wait a Few Years,” Yankee Woodlot, Coop. Extn. Service, Univ. of Maine, Orono ME 04469
Blumenstock, Bud, “Grading Christmas Trees,” Yankee Woodlot, Coop. Extn. Service, Univ. of Maine, Orono ME 04469.
Blumenstock, Bud, “Growing Tree Seedlings in the Home Nursery,” Yankee Woodlot, Univ. of Maine Coop. Extn., Orono ME 04469.
Chase, Nan, “Growing a Healthy Crop for Christmas,” National Wildlife, Dec.-Jan 1995, p. 24.
Cherim, Michael S., The Green Methods Manual – The Original Bio-Control Primer, 1988. The Green Spot, Ltd., Publishing Division, 93 Priest Rd., Nottingham, NH 03290- 6204.
Christmas Trees – From Seed to Sale, 1992, Tree Publishers, Inc., Lecompton, Kansas. 76 p., $7.00 – practical articles from back issues of Christmas Trees magazine – address below.
Christmas Trees magazine, Tree Publishers, Inc., P.O. Box 107, Lecompton, Kansas 66050; Tel. (913)887-6324; Subscription $10 for 4 issues. State growers’ associations provide the magazine as part of their membership.
Christmas Tree IPM Newsletter, Plant Pathology Dept., Cornell Univ., c/o Roxy Barnum, 319 Plant Science Bldg., Ithaca, NY 14853-5908; Tel. (607)255-3245. Biweekly from April through September. Suggestions for natural control. $15 for 8 to 10 issues.
Christmas Tree Production Manual, 1989, Virginia Cooperative Extension Service, Pub. 420-075, 212 pgs. $7.25, payable to Virginia Tech Treasurer, from Virginia Cooperative Extension Service, Distribution Center, 112 Landsdowne St., Blacksburg, VA 24060; Tel. (540)231-6192.
Comis, Don, “New Money-Making Options with Trees,” Agricultural Research, Nov. 1997
Davenport, O.M. and Russell S. Walters, “Christmas Tree Culture in Kentucky,” Misc. 346, Univ. of Kentucky, Ag. Experiment Station, Lexington, KY Donovan, Dave D., “Seedling Availability, Planting, Initial Care,” Oklahoma State Univ. Extension Facts No. 5024, Coop. Extn. Serv., OSU, Stillwater, OK
Granger, Clark A., Bud Blumenstock and Stanley W. Knowles, “Christmas Tree Fertilization,” Coop. Extn. Service, Univ. of N.H., Durham, NH 03824.
Hauge, Christy, Syd Hovde and Edward Steigerwaldt, “Wisconsin Woodlands: Christmas Tree Shearing,” Univ. of Wisconsin Coop. Extn. Service, Univ. of Wisc.-Madison, Ag. Bulletins, Room 245, 30 N. Murray St., Madison, Wisconsin 53715.
Hill, Deborah B., “Christmas Trees as an Alternative Enterprise,” Forest Farmer, June 1988.
Hill, Lewis, Christmas Trees – Growing and Selling Trees, Wreaths and Greens, Garden Way Publishing, 1989.
Howe, Gus, “Seven-Foot Rows are Plantation Key,” The New England Farmer, May 1994. Kapple-Smith, Diana, “A Christmas Business,” Country Journal, Dec. 1980.
Kentucky Christmas Tree Production Workbook, 1991, Coop. Extn. Service, Univ. of Kentucky, Pub. FOR-16 through 36, plus PPA-16 and ID-85, 90 pgs. 24 separate fact sheets on growing Christmas trees. $5 from Dr. Deborah Hill, Forestry, 201 Thomas Poe Cooper Bldg., Univ. of Kentucky, Lexington, KY 40546-0073; Tel. (606)257-7610.
Lamont, W.J., D.L. Hensley, S. Wiest and R.E. Gaussoin, “Relay Intercropping Muskmelons with Scotch Pine Christmas Trees Using Plastic Mulch and Drip Irrigation,” HortScience 28(3):177-178, 1993.
Lilley, William D. and Vivian J. Holmes, “Growing a Continuous Supply of Balsam Fir Wreath Brush,” Christmas Wreath Notes #4, Bull. 7089, Univ. of Maine Coop. Extn., Orono, ME 04469.
Loucks, William L., 1992, “Weed Control Options in Tree Plantings,” Kansas State Univ. Coop. Extn. Service, Manhattan, KS