By Roberta Bailey
Planting fruit trees can be a big step, a commitment to a place and to one’s self. Some people plant trees as soon as they settle on a piece of land, knowing quite a few years will pass before they see fruit. For others, that same knowledge keeps them from planting. The longevity of a tree can be daunting. The prospect of learning how to care for such a long-term project can be even more daunting.
As with any garden crop, the key to healthy plants and plentiful yields is the health of the soil. Healthy soil makes healthy plants that better resist pests and that bear earlier or larger crops. Unlike garden crops, fruit trees are only planted once.
An apple tree needs to be fed when it is planted and almost every year afterward. Some of the key nutrients need to go in the planting hole, while others can be added to the soil surface. Often the only time people think of feeding a tree is when it is old and failing, or in an intensive orchard where large annual crops are being removed. Most people would think to add nitrogen, but nitrogen is not an apple tree’s highest nutritional need.
Siting the Tree
Let’s start at the beginning. The planting site is directly related to the health and productivity of a tree for its entire life. You will be fighting a long uphill battle if you plant trees on poor soil or on a site with poor drainage. If that is all you have, don’t give up. You can grow fruit. Drainage can be improved or a terrace of good soil can be built up. If you are fortunate enough to have a choice of location, seek the best conditions before you plant.
The best soils for an apple tree are deep, light in texture, and well-drained, yet can retain moisture. The soil needs to be deep enough to encourage good root development. Good air drainage is also very important. Plant on a slope when possible; in winter, the cold air will move downward and the tree will be protected from the severest cold damage. In summer, the moving air rapidly dries foliage, minimizing fungal growth and the need for sprays.
On the other hand, avoid a site with extreme with exposure. Wind greatly dehydrates trees, reducing their overall performance and winter hardiness. Cold temperatures alone are not critical, if the wind is slowed. On exposed sites, plant windbreaks to the windward side. Some orchardists paint the trunks of the trees white with interior latex paint to reduce bark splitting during sudden winter temperature fluctuations.
Once you have decided on a site, plan at least one year of soil preparation before planting. Because of the difficulty of adding nutrients to a planted tree, soil fertility should be optimum before planting. Test the soil pH and add dolomitic limestone to bring it to 6.5 to 6.8. A good soil test will help you determine your nutrient needs. Apply rock phosphate for phosphorus and sul-po-mag for sulfur, potassium and magnesium. Large areas benefit from one to three years of green manures to add organic matter, increase overall nutrient levels, and aid in weed control. This green manure should be turned in and the area should be planted in a non-competitive grass species.
Some nutrients need to be added directly to the planting hole. For specific planting instructions, consult a good fruit growing book or planting guide. Feeder roots grow horizontally, so dig a wide hole deeper than the original growing depth of the tree. As feeder roots are shallow, be sure to mix the added nutrients into the hole at the previous soil level. Use the existing topsoil and subsoil to fill the hole whenever possible.
Calcium, magnesium and phosphorus bind tightly to the soil and do not move readily down from the surface into the major feeder root zone. Surface or top dressings take years to become available to the tree roots. The nutrients are best mixed with the topsoil at planting time, and later top dressed to prevent future deficiencies. Boron, sulfur and nitrogen are readily assimilated into the soil and can be top dressed.
Do not add nitrogen directly to the planting hole. Apple trees need very little nitrogen, amounts best attained through a gradual downward assimilation from top dressing. Too much available nitrogen promotes uncontrolled growth, which may not slow in fall, and may make the tree prone to winter kill or severe dieback. Barnyard manure can be spread around trees at a rate of ten pounds per tree.
Once your soil is mixed, fill in around your tree, adding water after every 4 inches of soil. Do not heel in the soil, but gently tamp it with your hand. Thoroughly soak the soil, making a retaining rim of soil at the edge of the hole. Water weekly throughout the first year.
Weed competition is hard on apple trees of any age. A straw or hay mulch reduces weed competition, retains moisture, adds nutrients, and increases microbial action and worm populations. A layer of cardboard beneath the mulch prolongs the weed free period and will also kill sod. Mulch should extend 4 feet from a young tree and to the drip line (the outermost reach of the branches) of an established tree. In winter, mouse guards are essential around a mulched tree.
A leaf analysis laboratory test is the best method of testing nutrient needs of planted trees. Leaf analysis indicates what nutrients the tree is actually absorbing, not just what is available in the soil. Leaf analysis, combined with soil tests and your keen observations, make a successful basis for soil supplementation.
In his talk “Mineral Nutrition of Fruit Trees” at the Maine Tree Crop Alliance-sponsored Apple Tasting and Fruit Show at Unity College last fall, Steve Page spoke highly of leaf analysis as a means of calculating your soil nutrient needs. Generally an analysis is done on 100 leaves picked from a tree in July. (Consult the extension service in your area for lab locations and specifics of testing.)
Based on leaf analysis, Steve was able to determine the nutritional needs of his orchard to compensate for what his fruit crop removed from the soil annually. The following figures are the general annual nutritional needs of a well-maintained orchard per acre.
Nitrogen (N) – 15 to 75 pounds. Used in the formation of chlorophyll and plant protein. Too much nitrogen leads to excessive vegetative growth and winter damage, poor fruit production, and watery core, a condition that reduces fruit quality and storage life. Topdress with barnyard manure or rich compost.
Phosphorus (P) – 10 to 25 pounds. Apple trees need very little phosphorus and Maine soils tend to have high levels. Bone meal and rock phosphate must be mixed into the soil to be available. Phosphorus is necessary for flowering, fruiting and good root development.
Potassium (K) – 120 to 200 pounds. Potassium is the major nutritional requirement of an apple tree. Hay mulch supplies potassium. If more is needed, sul-po-mag can be added to the soil. Potassium is used in root development and the production of chlorophyll.
Calcium (Ca) – 45 to 100 pounds. Calcium is difficult for trees to assimilate. It must be dug 10 to 12 inches below the soil surface. Calcium and magnesium are available in dolomitic limestone. Calcium can also be applied as a foliar spray in June and July. It is essential for plant cell walls, especially in young leaves and all new growth points.
Magnesium (Mg) – 10 to 25 pounds. Aside from dolomitic limestone, magnesium is available in sul-po-mag and Epsom salts, the latter sprayed at petal fall at a rate of 45 pounds per acre or 1 pound per tree. Magnesium plays a role in photosynthesis.
Boron, zinc, manganese and copper are minor mineral nutrients (micronutrients) affecting photosynthesis and enzymatic reactions. Boron (2 to 3 pounds per acre) can be applied in the form of Borax (from the store shelf) at a rate of 2 ounces per tree around the drip line at petal fall. Zinc (10 to 15 pounds) in the form of zinc sulfate can be sprayed before bud out and in the fall. Manganese (3 to 5 pounds) and copper (3 to 5 pounds) in the form of copper sulfate can be sprayed when the trees are dormant.
A pH level of 6.5 to 6.8 is imperative for proper nutrient absorption. Feeding the soil is long term. Foliar sprays are a quick fix, but are sometimes the only way to get nutrients into a tree readily. For a simple calendar of monthly organic nutrient and low spray applications, refer to The Orchard Almanac by Steve Page and Joseph Smillie.
The Orchard Almanac: A Spraysaver’s Guide, S. Page and J. Smillie. 145 pp. AgAccess, 1986.
Growing Fruit in the Upper Midwest, Don Gordon. 286 pp. U. of Minn. Press, 1991.
MOFGA Fact Sheet #3: “A Guide to Raising Apples Organically.”
Apples for the 21st Century, Warren Manhart. North American Tree Company, 1995.
Fedco Trees Planting Guide, J. & R. Bunker. 1995. Fedco Trees, P.O. Box 520, Waterville, ME 04903-0520.