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Highbush Blueberries

Blueberry bushes not only provide fresh fruit but also can be used as a source of fall color in a backyard planting. Blueberries are relatively easy to grow, provide about eight quarts of berries per bush at maturity, and the fruits are versatile and high in vitamin C.


Varieties

There are several blueberry varieties that are suitable for Massachusetts. Especially cold areas, like regions of Berkshire, Franklin and Hampshire counties, should not be planted to the earliest or latest-ripening varieties. Midseason varieties are more suited to these areas. Purchase two-year-old plants from a reputable nursery. Plants this size are easy to handle, become established quickly and bear fruit within a year or two after planting. Recommended blueberry varieties include:

Other varieties that may be worth growing on a trial basis only are Elizabeth, Elliott, Northland, and Patriot. For adequate cross-pollination be sure to plant at least two varieties that overlap in time of bloom.


Soil Preparation

Blueberry plants are shallow rooted and require soils that hold moisture well, but are also well-drained. Dry, sandy soils and heavy wet soils can be improved by adding a source of organic matter such as peat moss, well-rotted manure, compost, aged sawdust, or leafmold. Blueberries grow best in soils with a pH range of 4.6 to 4.8 but should do well in soils with a pH ranging from 4.0 to 5.2. An area where plants like laurel, huckleberry, wild blueberry, or pines are growing is usually suitable for highbush blueberries.

Soils should be prepared, and all preparations should be completed two weeks ahead of planting. Rows can be rototilled, or individual holes (two feet across by two feet deep) can be dug as early in the spring as possible. A mixture of equal parts of loam, sand, and organic matter should be placed in the holes before planting.


Fertilizing

Before planting. Since blueberries require acid soils, lime is not needed in a blueberry planting. Often, sulfur, sulfate of ammonia, or another acidic material must be added to lower pH (and increase soil acidity). Well-aged manure can be worked into the soil in the fall before planting.

After planting. About a month after setting out plants, apply one-half to one ounce of 10-10-10 (one to two ounces of 5-10-10 or equivalent) in a band around the base of the plant.

Following years. Increase rate of fertilizer by one to two ounces (of 10-10-10 or equivalent) per year until mature. When mature, blueberry bushes require about one-half pound of 10-10-10 (or equivalent) per year applied in April. In larger plantings, 40 to 50 pounds of actual nitrogen should be applied per acre.


Planting

Blueberry bushes should be planted in full sunlight for maximum fruit production. Set out plants as early in the spring as possible. Plant bushes one to two inches deeper in the soil than they were in the nursery, six to eight feet apart, in rows spaced eight to ten feet apart. After plants have been set in the holes, fill the holes three-fourths full with soil mixture (see "soil preparation"), and then flood the hole. After the water has drained, fill in the holes with soil and tamp it down.


Mulching

Mulching the plants with clean straw, sawdust, or wood chips will help conserve moisture as well as aid in weed control. A three to four inch layer of the above materials should be suitable. Generally, grass is allowed to grow between the rows of bushes, as long as the grass can be mowed frequently.


Watering

Mature blueberry bushes require one to two inches of water each week for best growth and productivity, especially during the harvest season.


Weed Control

Blueberry bushes, especially young ones, suffer starvation if weeds or lawn are allowed to grow too close. Blueberry roots are close to the soil surface and need to be protected against competing weeds. Mulching is the recommended method of weed control around plants.


First-Season Care

Blossoms should be removed from newly-set-out plants to encourage maximum growth. Extra water and/or additional fertilizer applications may be necessary if plants are not making much growth.


Pruning

Pruning is the most important aspect of blueberry culture. Annual pruning is necessary to invigorate the bushes, encourage annual fruit production, and prevent the bushes from overbearing. Until the bushes reach maturity (at about eight years old) remove only dead, broken, short or weak shoots. On mature bushes remove one-third of the oldest shoots each year, as well as any broken or diseased branches. Prune in late winter or early spring before growth begins.

Flower buds are produced on the end of a shoot's growth. The flower buds are plump and rounded, leaf buds are small and pointed. Each flower bud may produce a cluster of five to eight berries. If all flower buds are left on, too many berries will be produced and many will be small and worthless. Also, short, thin shoots will grow resulting in poor fruiting wood for the following year's crop. Bushes need little pruning during the first two or three years after planting; only short, weak twiggy growth need be removed.

After two summers in the field, all the plants should be ready to prune for a small crop (1/2 to 1 pint per bush). Remove the thin, twiggy growth and concentrate the potential crop on a small number of stout, fruiting shoots. By limiting the cropping to only the strong shoots, the bush will continue to grow rapidly. A heavy crop at this time dwarfs the bush.

Pruning Mature Bushes

After the fourth summer in the field, some canes may show a weakening due to heavy bearing. From this time on, the first step in pruning is to remove canes which have only small weak, fruiting twigs. They may be cut to the ground or to a strong side shoot near the ground. This will stimulate the sprouting of new canes from the base, which keeps a plant relatively "young." It also allows adequate sunlight to penetrate the bush and promote the setting of fruit buds.

With enough sunlight, the new canes will start producing fruiting laterals in the second year at a relatively low level in the bush and will be able to develop a large zone of fruiting wood in the third and fourth years. In a dense, crowded bush a new cane will take three or four years to produce nothing more than a tuft of fruiting twigs at the very top of the bush.

The number of old canes to be removed depends on the rate of growth over the past several years and varies considerably over six years old; it may be necessary to remove two canes annually due to changing growth rates.

After removing the older canes, the small twiggy growth is eliminated in favor of the stronger shoots. A limited amount of twiggy growth may be left in the lower portion of the bush. At this level shading is not a factor, and the fruit production from these twigs will add to the total crop.

Pruning Weakened Bushes

Blueberry bushes are often weakened by: overbearing due to improper pruning, poor soil drainage, insufficient fertilizer, drought injury, crowding, scale injury, and grubs feeding on the roots. After the undesirable conditions have been corrected, it is possible to rejuvenate the plants by removing 1/3 to 1/2 of the old bush. This is accomplished by making large cuts at ground level. The remaining portion of the plant is allowed to bear heavily. The remaining old canes are removed the following spring.


Pests and Diseases

Birds are a major problem with blueberry growing. Bushes often must be covered with netting to protect developing berries from birds. The major insect pests on blueberries are apple maggot, fruit worms, and Japanese beetles. The major diseases are mummy berry, twig blights (caused by several different fungi), and viruses.

Disease prevention is a good rule to follow when growing any small fruit. With blueberry growing, the following cultural practices will help prevent serious problems with most diseases.

  1. Plant disease resistant varieties when possible. Purchase healthy plants.
  2. Regular pruning helps to increase production, removes diseased plant parts, increases air circulation within the plants, and helps initiate fruit bud formation.
  3. Prune out all diseased and insect-infested wood. Remove any wood that is broken or damaged. All diseased wood should be burned to prevent reinfestation of healthy plants. Keep plants free from weeds and debris. Rake under the bushes.

Disease Symptoms

"Mummy berry" is the most serious blueberry disease in Massachusetts. It is a fungus which first appears on newly emerging stems and flower clusters causing them to blacken and die. Later, spores infect blossoms. Developing fruit become tan and hard. These "mummified" berries eventually fall to the ground. Fungal spores overwinter inside the mummified berries. Removing infected berries is essential in preventing the disease from reoccurring. Raking and shallow cultivating between plants helps remove mummified berries. Applying 50 percent urea prills in the spring reduces spores from the mummified berries thereby reducing infections on plant growth.

"Fusicoccom (Godronia) canker" begins on plant parts near the ground, and appears as small reddish spots on the canes, often around a leafscar. These spots enlarge, forming a bullseye pattern. Fusicoccum cankers eventually girdle canes causing wilting and die-back.

"Phomopsis twig blight" causes symptoms very similar to those caused by Fusicoccum canker. Spores from infected plant parts are released in the spring and infect smaller twigs. Flagging and dieback follow initial twig infections. Leaf spots as well as crown infections can also occur.

Planting blueberries in optimal sites and proper pruning practices help to prevent these diseases. Winter cold encourages both Fusicoccum and Phomopsis. Practices which reduce winter damage, such as fertilizing in spring rather than fall, will decrease chances of encountering these diseases.

"Anthracnose" is often a problem on developing fruit. This fungus also overwinters in diseased twigs, spurs, and stem cankers. The spores are spread by rain and wind. Infected fruit bear bright pink spore clusters. Proper pruning practices help control this disease.

"Botrytis" causes rotting on ripening fruit under moist conditions. Encouraging good air circulation and frequent picking reduce this problem.

Nutritional problems: Often, blueberry leaves show a yellowing, or chlorosis, especially between the leaf veins. This is usually a result of the blueberry roots being unable to take up iron from the soil. This "iron deficiency" is more often than not related to soil pH, or acidity. Blueberries should be grown in a pH range of 4.2 to 5.0. Above pH 5.0 the plants show this typical deficiency symptom. If your plants show yellow leaves (as described above), please have your soil tested to determine if the problem is pH related.

For chemical control recommendations, please refer to the current small fruit pest control guide.


Other Problems

Problem: The leaves on my blueberry bushes are turning yellow.

Cause: Interveinal yellowing (chlorosis) of blueberry leaves is most often caused by iron deficiency. When the soil pH is too high, blueberry roots cannot take up iron, and the plant appears to be iron deficient. Have your soil tested for pH level before you apply iron. Often, correcting the pH level is all that's needed.


Harvesting

Highbush blueberries are often harvested too early. After the berries turn blue, they should be left on the bushes for three to seven days to ripen and develop their full flavor and sugar content.

Berries should be harvested at two to three day intervals to discourage Japanese beetles, other insects, and fruit rots from entering ripening fruit.


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This page was last updated on November 16, 2002