Highbush Blueberries

Winter 2007-2008
Highbush-blueberries-in-orchard
A section of Rivard’s Farm shows well pruned and mulched highbush blueberries. Photo courtesy of David Handley.

Highbush blueberries are native fruits that have been here for tens of thousands of years. They were largely ignored by the first Europeans in America, although Native Americans used some—mostly for pemmican, which included mashed blueberries and animal fat. 

In the 1900s, Dr. Coville of the USDA, working with Elizabeth White, made selections from the wild and crossed them to make basis of varieties available today. Breeding programs now exist around the world and have expanded the range of commercial growing regions and popularity of this fruit.

Like rhododendrons, these Ericaceous family members prefer to grow in areas with very acidic soils with a good layer of peat-like organic matter over very well drained soil. In swampy areas, they’re on hummocks, so roots aren’t submerged. The roots of highbush blueberries don’t penetrate clay soil well. They have a very fibrous root system and survive without root hairs by associating with a mycorrhizal fungus that helps extract nutrients from soils. The plants have woody canes and fruit on one-year-old shoots. Shoots of the current year’s growth develop buds that will produce fruit next summer. Older shoots harden and won’t produce fruit again unless pruned.

Highbush blueberries also have value as landscape plants. Some catalogs rate varieties for their yellow-orange to deep red fall color. Some commercial plantings in Maine have existed for over 50 years.

Site Selection

Plants need a well-drained, preferably sandy soil, and they won’t do well with a hardpan that holds a lot of water in spring. While normally an understory crop, shade strongly limits production, produces uneven plant growth, and fruits will be small and will ripen unevenly.

Wind can cause winter injury, so plant a windbreak. The Natural Resources Conservation Service (nrcs.usda.org) can provide guidelines and may offer incentive programs for planting windbreaks.

A gentle slope with good elevation will help drain water and air, protecting plants from bud-damaging spring frosts. Since frost tends to settle in low areas and winds are worst on hilltops, Handley recommended planting on the slopes. A nearby water source helps.

Prevent perennial weeds with cover crops, crop rotation or fallow periods, ideally for a couple of years before planting. Blueberries have good potential as an organic crop, because few pests bother them, and they do well on many Maine soils.

Soil selection

If the soil pH is 6.0 or above, add sulfur to attain a pH of 4.8 to 5.2 (see Table 1) – but not much lower. Adding sulfur year after year can create a pH of 4.0 or 4.2 – too acidic to supply some nutrients to blueberries.

Maintain organic matter at 2% to 4% or even higher, and don’t add unneeded nutrients. Adding chicken manure annually, for example, can oversupply phosphorus. Watch the magnesium (Mg) Calcium (Ca) and Potassium (K) balance. Excess soil K (e.g., from dairy manure) reduces Mg availability, and Mg is very important in highbush blueberries.  This common deficiency can be countered by adding Epsom salts to the soil.

Table 1 – Pounds of ground sulfur/A to lower pH to 4.5

pH Sand Loam Clay
5.0 175 530 800
5.5 350 1050 1600
6.0 530 1540 2310
6.5 660 2020 3030
7.0 840 2550 3830

Soil pH takes about a year after Sulfur (S) additions to change, and sandy soils change faster than clay soils. If you’re planting in clay soil (which is not recommended), more S is required to lower the pH. A lot of organic matter is also needed to open the tight structure that otherwise hinders blueberry root growth.

Sulfur is usually added as prills or as ground sulfur, with more finely ground S reacting faster. Prills tend to react slower, but their application doesn’t create a cloud of dust.  The price is about equal. Handley rarely recommends aluminum sulfate. It reacts fast, but it adds a lot of aluminum to the soil.

Tree Selection

Select very hardy types that will mature on your land.  Most varieties of highbush blueberries were bred in the mid-Atlantic and upper Midwest and don’t do well here.  Focus on varieties from Augusta.  “If you live north of Augusta, all bets are off,” he said, although a grower in Caribou has had luck with low-stature plants in a spot that gets a lot of snow. Most varieties are guaranteed to USDA plant hardiness zones 5 or 6; most of Maine is in zone 4.  (The lower the number, the colder the winter.)

Handley suggested that only growers south of Portland try such varieties as ‘Bluetta’ and ‘Earlyblue.’ which break buds early. Frost tends to kill these buds farther north. Early varieties also tend to lack fruit quality.

Some very late varieties, such as ‘Lateblue,’ ‘Coville’ and ‘Elliot,’ have good fruit, but they don’t mature until the first week of September, limiting production where frost comes by September 10 or 15.  “‘Eliot’ is on my recommended list for southern Maine but not for northern Maine,” said Handley.

Types of Highbush Blueberries

Handley discussed the following highbush varieties, in order of ripening:

Patriot

One of the earliest to mature; developed in Maine; very large, quality fruits with good flavor; hardy; does not produce new canes vigorously, so yield can be shy; with good soil fertility and lighter pruning than normal, it will be productive; susceptible to mummyberry and witch’s broom.

Northland

A cross between highbush and lowbush species; 4 to 5 feet or taller in fertile soils; unlike ‘Patriot,’ a spreading bush, with many rhizomes sending up many shoots and forming a thick hedge if poorly pruned; early to midseason; a good pollinator for some other varieties; relatively small fruit size is an issue in some states, but many Mainers are used to and some even seek wild-type; smaller berries for jams and pies; doesn’t have a great bloom (the waxy coating that gives blueberries a desirable, light blue appearance).

Blueray and Bluecrop

Very nice, older USDA varietie; ‘Blueray’ is mid-early, ‘Bluecrop’ is grown in midseason; both hardy and have large, nice looking fruit, with ‘Blueray’ fruits a little bigger; ‘Bluecrop’ has some mummyberry resistance; ‘Blueray’ is quite susceptible; vase-like habit of ‘Blueray’ can challenge pickers when some branches are on the ground; tend to break under heavy snow load.

Nelson

Mid-late type, can round out the season in Maine; large, quality berries not as large as those of ‘Blueray’ but have nice bloom, good flavor and yield; very hardy; seems to get mummyberry in Handley’s trials.

Jersey

Gave highbush blueberries a somewhat bad name; mildly sweet, but not as flavorful as wild type; late-midseason, medium-small fruit with good bloom; hardy, but some years not so hardy as others; mummyberry resistant; adapted to wider range of soils than others; should do better than others on heavy or poorly drained soil.

Southern Maine varieties

‘Meador’ – Midseason; hardy; medium-large, quality fruits; yields “so-so.”

‘Elizabeth’ – Mid to late season; large, quality fruits; yields vary, especially with fluctuating spring temperatures.

‘Toro’ – Mid to early season; large, quality fruit; hardiness not well tested.

‘Elliot’ – Trial for a late market, but a lot of berries will be lost in northern Maine; fruits medium sized, attractive; hardy; mummyberry resistant.

‘Blue Gold’ – Mid to late season; medium sized, good fruit; relatively hardy but hasn’t done well in Monmouth area.

‘Herbert’ – Midseason; large, soft fruits unsuitable for mechanical picking or processing industry, but good for hand picking; good hardiness and yield, but suffers with wildly fluctuating spring temperatures.

Half-High Blueberries

These berries are crosses between highbush blueberries (Vaccinium corymbosum) and lowbush berries (Vaccinium angustifolium). They come from a Minnesota breeding program, and survive winter better than highbush because they’re covered with snow better. They’re also good for edible landscapes.

‘St. Cloud’ – Promising in very cold areas; about 4 feet tall; spreading growth habit; berries are a good size, dark (without much bloom), very flavorful and productive; recommended for very cold sites, but may not be the best in warmer areas.

‘Northblue’ (30 inches tall), ‘Friendship’ (24 inches), ‘North Country’ (24 inches) – Good around the house, in rock gardens, to feed birds and yourself; nice fall color; pretty spring flowers; not recommend for commercial production.

Pollinating Highbush Blueberries

Some blueberry varieties require cross pollination. To be safe, plant at least two varieties that flower at the same time, unless wild blueberries are nearby. Blueberries don’t appeal to honeybees, because the flowers have long corollas, and nectaries are deep in the flower, where honeybees’ tongues can’t reach. But bumblebees love them, as do small, solitary bees that crawl inside the flowers. If forced (if enough hives are set out), honeybees will work the flowers. Carpenter bees chew a hole in the side and get nectar without pollinating; then honeybees use the same entry hole.

Planting

Plant one- or two-year-old plants in early spring rather than fall. Rooted cuttings are less expensive but take two more years to produce. Three-, four-, five- and 10-year-old plants are too expensive for large plantings.

Dig a large planting hole (but not too deep) and spread the roots in it. Most of the roots are in the top 6 to 8 inches of soil. Backfill the hole with a 1:1 blend of soil and organic matter—preferably compost. Well-rotted sawdust also works, but fresh sawdust robs roots of nitrogen. Peat works, but is expensive and must be moistened before use. Don’t put fertilizer (except compost) in the planting hole because it burns the roots. Set plants at the same depth as at the nursery and water them thoroughly. At planting time, prune only broken branches, or branches heading in the wrong direction. Plants will take a year to catch up from heavier pruning.

Spacing

Set plants 4 to 6 feet apart within rows, or 2 to 4 feet for smaller varieties, especially half-high plants. With some of the larger, spreading plants such as ‘Bluecrop’ or ‘Blueray,’ 6 feet between plants will provide sufficient space for pruning and picking. Leave 8 to 12 feet between rows to get equipment in without knocking fruit from plants. These recommendations result in 650 to 800 plants per acre.

Tree Care

First Season Care

To establish a planting, don’t just rototill strips in a hayfield. The hay will come back readily and overtake the plants. Prepare the whole field, increase the fertility, get ahead of weeds and then plant. Cultivate between rows and keep the plants watered. Handley prefers a trickle system, although overhead is fine.

The first spring, rub flower clusters off to help plants get established. Fertilize very lightly about a month after planting, when roots are somewhat established. A 1:1:1 balanced fertilizer is recommended, so that each plant gets about 1/10 of an ounce of actual nitrogen fertilizer.

Second Year

Mulch with 4 to 8 inches of wood chips or bark, but not sawdust. Establish a ground cover between rows. A weak perennial, such as hard fescue or bluegrass, is good. Avoid a contractor’s mix or pasture mix as these tend to have very aggressive grasses and aren’t monitored well for weed seeds. The hard fescue or bluegrass mix may take two to three years to get established. After that, it only needs to be mowed only a few times a year. Don’t sow legumes: Clovers will come in on their own and can even become weeds because they can grow through mulch. Clovers can also carry tomato ringspot and other viruses that can affect blueberries.

Fertilizer

Nonorganic growers may use an acidifying fertilizer such as Muracid, and organic acidifying fertilizers are becoming available. If the soil pH is between 4.8 to 5.2, any fertilizer that supplies sufficient Nitrogen (N), Phosphorus (P) and Potassium (K) is fine. The form of fertilizer won’t affect soil pH much in the short term, but repeatedly using acid fertilizers may eventually make the soil too acidic.

Blueberries, unlike most plants, tend to take N up in the ammonium (NH4+) rather than nitrate (NO3-) form, so growers tend to use such N sources as ammonium sulfate. Regular additions of compost, fish meal or other N fertilizers are fine as long as plants are growing sufficiently.

How to Fertilize

Young highbush blueberry plants don’t need much fertilizer (see Table 2). With a 7:7:7 product, such as Muracid, apply about 2 ounces per plant. Then, increase that rate by about 2 ounces per year until the plant is six years old. Eventually apply about 12 ounces per plant—half at budbreak (when buds first swell in spring) and half six weeks later, when green fruits first appear. Increases in subsequent years may be necessary if, after six years, growth rate and height aren’t as expected. Organic fertilizers are usually a slow release, so split applications may not be necessary.

Apply fertilizer in a ring extending 15 inches from the base of the plant – or at least up one side of the row and down the other – to prevent uneven growth.

Table 2.  N Application/Acre/Year
Age of Plant Annual N/A/yr. (lbs.)
2 15
3 20
4 27
5 35
6 45
7 55
8 65

While organic growers can’t use ammonium sulfate or urea, the N rates in the table show that blueberries are not hungry plants. “They’re very good at mining the soil for what they need, and overfertilizing can cause winter injury and encourage weed growth,” said Handley. Plants should have about 10 inches of new, dark green growth by the time green fruits appear. A lot more growth means plants have too much N; less means too little.

Highbush blueberries have a spring flush of growth, then the bud tip dies. After this, a secondary bud breaks and is followed by a second flush of growth, which produces most of the following year’s crop. The second fertilizer application (recommended to nonorganic growers) provides N for this second flush and helps set flower buds for the next year.

Pruning

When to Prune

During years one to three, encourage roots by removing only broken branches and weak growth. For the first two or three years, remove most flowers. To encourage upright growth, remove branches that grow along the ground.

In years four and beyond, a mature bush should have six to 12 canes ranging from one to six years old coming up from the ground. Remove weak, fruiting shoots and anything in excess of 12 upright canes. No individual cane should be more than six years old, since older canes are big, tall and mostly vegetative with very small fruit.  Canes about three to six years old are most productive and have the best fruit.

Prune in late winter, when plants are dorman. This should be done as soon as you can get into the planting – commonly in March, although the first of the year is fine if the snow is low enough.  Fall pruning can break dormancy and increase winter injury. Even if dormancy isn’t broken, fall-pruned plants tend to flower earlier, subjecting more of the crop to frost.

How to Prune

With loppers, remove one to four of the oldest canes that are over six years old. Cut them to the ground, unless the bush is producing only a few new shoots. In this case, “stump” the plant by cutting it about 8 inches high. Breaks from the stump will create new shoots. Stumping can work well with a variety like ‘Patriot,’ which doesn’t produce many new shoots, Most varieties, however, produce lots of new shoots. After this, thin new canes, leaving one to four of the most vigorous; these will replace the old canes.

Next, in the canopy of the plant, use hand shears to remove shoots with weak growth (under 6 inches long and with few or no fruit buds.) Remove winter injured shoots, which have chocolate-brown colored buds. Keep strong shoots that have a good balance of flower and vegetative buds. Flower buds are teardrop-shaped; smaller, pointed buds are vegetative. Remove 50 to 75% of the fruit load from the bush, since blueberries habitually over-fruit, which decreases fruit size and quality; delays maturity; and can set plants up for biennial bearing.

Renovating Neglected Bushes

Neglected bushes can be cut down with a chainsaw. Old, established plants with good root systems will send up new shoots, and three or four years later, the plant should set a good fruit load. An alternative is to remove one-fourth to one-third of the oldest canes with a saw every year for three or four years. At the end of the fourth year, some four-year-old canes will be producing.

Harvesting Highbush Blueberries

Harvest may last from late July or mid-August until frost. Planting just a couple varieties of highbush blueberries that ripen uniformly can concentrate the season. Planting early, mid- and late-season varieties can extend the season.

Harvest when fruits they have been completely blue for one to three days. Fruits with some green color will still be very tart. Harvest fruit for market when it’s cool and dry— fruit harvested in the heat of the day will deteriorate quickly. Cool fruit immediately in a refrigerator or in an air-conditioned shed. Blueberries should be stored at 32 degrees. They won’t freeze at this temperature because they have so much sugar in them. Put them in flats or containers. Fruits stay in much better shape in half-pint containers than in quarts.

Mechanical harvesters are available but cost $40,000 for a tractor-pulled unit and $150,000 for a stand-alone model. Most mechanically harvested fruits have a short shelf life and, thus, go to processors.

Selling your Highbush Blueberries

Pick-Your-Own may be the most popular marketing method in Maine, but customers are changing. There’s elders who, remembering the Depression, pick a lot of fruit for food security, to younger couples with kids who come for exercise, fresh air and entertainment and pick only a couple of quarts. The market is still pretty good, and blueberries command a good price.

Highbush blueberries ripen when tomatoes and sweet corn are ready, so you may not have time to deal with the crop or PYO customers who can require a lot of patience. The pre-picked market is growing, but labor for picking is a problem.

To sell retail, talk to potential buyers first. They may already deal with growers in Massachusetts or New Jersey.  Make sure buyers know you and the quality of your product and service. Don’t miss deliveries.

The demand for more wholesale highbush blueberries is questionable, given the many big growers in New Jersey, Michigan, New York and Connecticut. Still, distributors may want local fruit.

Problems

Weeds

To grow highbush blueberries organically, preplant weed control with cover crops or fallowing is critical.  Within rows, 6 to 8 inches of wood chip or bark mulch work, but don’t use woven ground cloth:  Blueberry roots don’t grow well under it.  Sawdust alone will crust, and water will run off it and onto grass.  Blend sawdust with wood chips or other porous material, or break up the crust.

No herbicides are OMRI-approved for blueberries yet.  Vinegar may be in the future, but plants would have to be shielded from it.  Handley believes that good preplant control, mulches and vigilant pulling by hand will solve weed problems.  Otherwise fruit size and yield decrease.

Winter injury occurs after cold, and especially fluctuating, temperatures.  After 600 to 800 hours of chilling, blueberries break dormancy, and sap flows if plants are exposed to warm February temperatures, creating potential for winter injury—visible as brown, desiccated shoots.  To avoid this, plant hardy varieties and windbreaks.  Buds below the snow line are pretty well protected.

Birds

Netting is the best bird repellent but is very expensive. It requires a structure around all bushes rather than nets over individual bushes.  Individual nets make tending bushes and harvesting too difficult, and nets won’t last long.

Put netting up when berries are just turning blue; remove and store it when picking is over, because UV light degrades the plastic.

Deterrents such as scare eyes and owls work for a few days, then birds become accustomed to them.  Set them up as fruits ripen, move them two to three times daily, and take them down after harvest so that birds don’t become accustomed to them.  Alarms, such as the sound of bird alarm calls, cost $200 to $1000, depending on the area to be covered, and may work for a couple of weeks—or not.  Handley has had the best luck with 3/8-inch-thick Mylar tape that is shiny silver on one side and red on the other. He puts posts at row ends and runs tape a few inches over the bushes, putting a few twists in it.  Wind blowing the tape makes a noise like a helicopter and frightens birds.  Eventually they become accustomed to the tape, but it works longer than other deterrents.

Predatory birds—owls, hawks and eagles—will frighten other birds from the area.  Blackbirds, starlings and grackles—are problems.  Handley saw one flock land on netting and weigh it down so that the birds could peck through the netting to get the fruits.

Polyester row covers can exclude birds, but the covers heat the air, possibly to over 100 degrees, harming fruit.  If used, the material must go to the ground and be anchored.

Old nylon fish netting, sometimes available along the coast, works well.

Mummyberry

This fungus can be a big problem in wet springs.  It overwinters in mummified fruit in the field, and mushroom-like structures form in the spring from the mummified fruit that shoot spores into the air.  These land on the shoot and cause “shoot blight,” which looks like frost injury.  Then the fungus forms oozing masses on dead and dying leaves.  Rain hitting the gooey masses drips onto flower buds.  Infected buds create infected fruits, which start to turn blue but then turn a tan-rose color and shrivel, die and fall off, depleting most of the crop.  Most varieties grown in Maine are susceptible to mummyberry.

Handley suggests removing and destroying mummified fruits or fruits showing any symptoms, such as a pinkish color, a few times before crops ripen.  Later, bring two buckets to the field:  one for good berries and one for infected.  In early spring or late fall, rake up as many mummies as possible from the ground; or lightly cultivate them into the soil; or add 4 inches of mulch over last year’s mulch.  Mushrooms won’t grow through the mulch.

Fungicides applied from bud break to flower bud give reasonable control, but no OMRI-approved fungicides work well.  A late, dormant spray of lime-sulfur in the spring may reduce mummyberry and some shoot blights, but won’t give great control.

Witch’s Broom

In spring, thickened, rubbery growth with odd-looking leaves may occur on branches and in the crown of the plant.  The bark is light tan, cracked and shriveled, and these shoots never fruit.  The problem is caused by a rust fungus that has balsam fir as its alternate host—so it’s fairly common here.

Handley has seen old, established bushes that were heavily infested with the systemic disease (it moves through the plant) but were still producing a reasonable crop, although plants slowly become less productive.  While most literature says to remove plants as soon as witch’s brooms appear, Handley says that’s not economically feasible for most of us.  He takes out the entire cane where the broom occurs and destroys it. If brooms are coming from the base of the plant and no new, uninfected cane growth is coming, replace the bush.

Growing Christmas trees and highbush blueberries together probably won’t work, and the recommended separation between blueberries and balsam fir of at least 1,000 feet is difficult to get in Maine.  On balsam fir, the disease simply causes small spores on the underside of leaves and is not problematic.  Handley has seen varietal differences, but doesn’t have enough information to make a recommendation yet.

Blueberry Maggot

The fruit fly responsible for the maggot is a little smaller than but similar to a house fly.  It has three white bands on its abdomen, and its wings are translucent but have an F pattern.  Flies lay eggs as berries start to turn blue.  The oviposition hole looks like the fruit was punctured with a needle.  Eggs hatch and larvae (maggots) develop in the fruit, causing the fruit to cave in on itself.  Customers are upset when they make jam and maggots float to the top, but the maggots can be skimmed off.

Pyganic, an OMRI-approved insecticide labeled for blueberry maggot, is effective for only about 24 hours, so it has to be reapplied.  Yellow sticky boards or red sticky ball traps can be hung around plantings.  As soon as one adult is trapped and identified, apply Pyganic again, and clean the traps.  With only a few bushes, one sticky trap per bush gives good control.  A pheromone can increase trapping, but one trap for every bush or two is still needed.

Japanese Beetle

Japanese beetles, present especially in southern Maine, are moving north rapidly.  They tend to feed on foliage, and blueberries can tolerate 25% defoliation without yield reduction.  Once fruits start to ripen, though, the beetles start to eat them, especially in a dry year; and customers don’t like to see the beetles.  Knock the insects into a bucket of soapy water in the morning, when they’re sluggish.

Pyganic will knock beetles off the bush but will not control them.  Surround, a kaolin clay spray, controls beetles by making bushes difficult to recognize, but customers may question whether they’re seeing a “nasty spray residue.”

Traps, such as Bag-a-Bug, usually have two baits—a sex pheromone that attracts males, and a floral scent that attracts females.  Unfortunately, traps attract bugs from a distance (Japanese beetles can fly for miles), and many beetles land near but not in the trap, so traps can increase damage.  You can put them at least 100 feet from the field to draw the beetles out of rather than into plantings.  Treating sod-feeding grubs with Bacillus papillae (milky spore disease, Doom) requires treating the whole county to be effective; the material does not survive well in Maine; and the product has lacked quality lately.

Voles

Voles can be a problem, especially with mulch, but mowing grass between mulched rows will discourage them.

Economics

Establishment costs $4,000 to $6,000 per acre, mostly for plants and labor.  Bird netting is also expensive.

Maintenance costs are about $6,000 to $7,000 per year, mostly for harvest and pruning labor.

Net returns above cost should be $2,000 to $6,000 per acre.  Some people are doing worse (especially if they’ve had winter injury); some are doing better (especially with a well-to-do clientele and a good labor source).  These figures reflect yields of 4,000 to 8,000 pounds per acre and prices of $1 to $2 per pound.  A PYO farm should be able to get more than $2 per pound.

From talks by David Handley of Maine Cooperative Extension Service and Jerry Rivard, who cultivates 2,000 blueberry plants in Springvale, Maine, at MOFGA and Cooperative Extension’s 2006 Farmer to Farmer Conference in Bar Harbor.

Now that you know how to plant highbush berries, it’s time to start your own orchard.

Sources of Plants

Fedco Trees, PO Box 520, Waterville, ME 04903, www.fedcoseeds.com
Nourse Farms, 41 River Rd., South Deerfield, MA 01373, 413-665-2658, www.noursefarms.com
Hartmann’s Plant Co., PO Box 100, Lacota, MI  49063, 269-253-4281, www.hartmannsplantcompany.com|
DeGrandchamps Farms, 76241 14th Ave., South Haven, MI 49090, 888-483-7431, www.degrandchamps.com/

Further Resources

Growing Highbush Blueberries, University of Maine Cooperative Extension
Bulletin #2253, David Handley, www.umext.maine.edu/onlinepubs/htmpubs/2253.htm
Agricultural Alternatives Fact Sheet, Highbush Blueberry Production, Penn. State University, https://pubs.cas.psu.edu/PubDept.asp?varDept=2&offset=15
The Highbush Blueberry Production Guide, $48, Northeast Agricultural Resource and Economic Service NRAES publication 55, Ithaca, N.Y., www.nraes.org

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