How to Cultivate the Bushes That Yield This Delicious Berry
The Blueberry is a native American fruit harvested from wild plants since the country was settled. About 1910 the late Dr. F. V. Coville of the United States Department of Agriculture began the domestication of the High-bush Blueberry. A breeding program based on selected wild types has produced through the years a number of varieties vastly superior to their wild ancestors. Considerable research on cultural problems has developed a body of knowledge on which a highly profitable and extensive commercial industry is growing rapidly.
The High-bush Blueberry, Vaccinium corymbosum, is the species which has been improved, and the varieties developed from it are those on which the cultivated Blueberry industry is founded. Extensive areas of the Low-bush Blueberry, V. angustifolium, in Maine are managed for commercial production. V. myrtilloides, another Low-bush type, yields considerable fruit.
In the deep South V. Ashei, the Rabbiteye Blueberry, is cultivated to some extent. Several other species are locally important sources of wild fruit.
The cultivated High-bush Blueberry is grown principally in New Jersey, Michigan, North Carolina, and to a lesser extent in the other northern states. It will grow about as far south as it can experience the approximately 700 hours of temperature below 40° needed to break the plant’s winter rest period. Minimum winter temperatures of 20° to 25° F. below zero are about all that the hardier named varieties can stand without killing of the wood.
The soil requirements of the Blueberry are very specialized, being unlike those of the other fruits and farm crops. The wild Blueberries grow on moist, sandy, acid soils and the cultivated varieties require similar soils. Sandy loams, if moist, acid, and high in organic matter, may be used, but compact clay soils with a high pH are wholly unsatisfactory. The optimum pH for Blueberries ranges from about 4.0-5.2. The symbol pH is a measure of soil acidity; see Soil Acidity.
Although moist soils are desirable, the water table should not be nearer the surface than about 14 in., nor lower than 30 in. during the growing season. Natural Blueberry soils are usually high in organic matter, often of a peaty nature. These soils often have growing on them Rhododendrons, Azaleas, Mountain Laurel and wild Blueberries, and the cultivated varieties may be expected to thrive on similar sites.
It is often possible to modify unsuitable soils for growing Blueberries on a small scale in the home garden. The acidity of the soil may be increased by the addition of sulfur. The addition of a pound of sulfur to 100 sq. ft. of a light sandy soil will lower the pH from 5.5-4.5. Heavier soils will require 3-4 times as much sulfur. The sulphur should be thoroughly worked into the soil to a depth of at least 6 in. a year before planting the Blueberries.. The acidity should be checked again before setting the plants.
Soil porosity may be increased by working peat into the soil at the rate of a bale to 100 sq. ft. Sawdust may also be used.
If Blueberries must be grown on clay soil sites, the clay should be removed to a depth of 18 in. and a width of 4 ft., and the hole filled with a suitable Blueberry soil. If the adjoining soil contains much lime, it will be necessary to acidify the “made” soil at intervals as pH tests indicate the need.
Frost pockets, or sites where air circulation is poor, are much colder in winter and on frosty nights when the plants are blooming, than sloping sites. Mummy berry, a fungus disease of the berries, is less troublesome where air circulation is good.
Home gardeners planting a few bushes should keep them away from the roots and shade of nearby trees or the plants will be weak and unproductive. The Blueberry needs full sun all day to produce good crops of fruit.
Varieties of Blueberries
About 40 varieties have been named since the Blueberry improvement work started, but many of the older ones have been superseded by the more recent sorts. Cabot, Concord, June, Pioneer, Rancocas and Rubel are older varieties still grown, but they are inferior to the new sorts. Jersey, Atlantic, and Pemberton are good standard sorts. Stanley is of superior quality but not as productive as the others. Dixi is one of the largest and is suitable for home use. Weymouth is very early but of low quality. Coville and Berkeley are newer sorts that will be widely planted when better known. Coville is one of the latest to ripen. Still newer and promising are Earliblue (to replace Weymouth as an extra early sort), Bluecrop, Herbert and Ivanhoe. Murphy and Wolcott are new canker-resistant varieties suited to North Carolina conditions. In eastern North Carolina and southward through the Gulf Coastal states and westward to Arkansas, the Rabbiteye (Vaccinium Ashei) varieties should be grown. Black Giant, Hagood, Owens and Myers are good varieties of this species. Calloway and Coastal are recently introduced and promising.
Blueberry varieties are mostly self-fertile, but larger berries and a higher percentage of fruit-setting may be expected if cross-pollination by another variety is provided. This may be done by planting every third row to another variety. Bumblebees are the pollinating insects.
Propagation of Blueberries. Blueberries are usually grown from hardwood cuttings, but the operation is more difficult than with many other plants. The cuttings root with difficulty and considerable skill and experience are needed to propagate the plants profitably. The small-scale planter will find it more satisfactory to buy the plants from nurseries specializing in Blueberry propagation.
The cuttings are rooted in a ground bed filled with a mixture of half peat and half sand to a depth of 6 in. The cuttings, 4-6 in. long, are inserted in the rooting medium in early spring and covered with sash and lath or burlap shade. Shallow trays, 4 in. deep, suspended in a box and filled with peat, are also used for rooting the cuttings. Ventilation and watering must be very careful. The cuttings are usually rooted by July, but remain in the frames until the following spring, when they are lined out in the nursery row for a year, after which they are sold as 2-year plants. One-year plants are rooted cuttings from the propagating frame.
Softwood cuttings taken in July are sometimes used to propagate Blueberries.
Planting stock should be obtained from nurseries specializing in Blueberry plants. The two-year plants are the better size for most purposes, but rooted cuttings may be used, provided they are given nursery care with watering if the weather is dry.
The plants should be set as early in the spring as the soil can be worked without packing it.
Late fall planting of the 2-year plants is satisfactory if soil or sawdust is mounded up around the plants to prevent them from being heaved out of the ground by frost action during the winter. On soils that are inclined to be too wet, the plants should be set on low ridges or mounds.
The plants are set 4-5 ft. apart in rows 8-10 ft. apart. Peat moss may be mixed with the soil at planting time at the rate of half soil and half peat in a hole 2 ft. across and 6 in. deep. The peat is especially desirable in soils that are not the best Blueberry soils. No fertilizer should be used at planting time and usually not during the first growing season.
Care of the Planting
Blueberries are shallow-rooted, and tillage operations should be done with that in mind. Cultivation should be shallow and frequent enough to control the weeds. Mulching is much superior to cultivation for Blueberries, and sawdust has proved to be an excellent mulching material. Peat moss, or oak leaves, may be used if sawdust is not available. The mulch conserves moisture and prevents root injury from cultivation, an important thing with the shallow-rooted Blueberry. It may be applied at any time and to a depth of several inches if an abundant supply is at hand. Either hardwood or softwood sawdust is suitable and there is no harm in using fresh sawdust.
Fertilizers. Complete fertilizers of the 7-7-7 formulas are usually recommended for Blueberries, but experimental work has shown that nitrogen is the element that should be applied, as the other elements are usually available in sufficient amounts in all except the poorest soils. Ammonia nitrogen is much superior to nitrate nitrogen for Blueberries, and this should be obtained from sulfate of ammonia, especially in soils near or above a pH of 5. In very acid soils, nitrate nitrogen may be used.
Beginning with the second spring, the sulfate of ammonia should be applied at the rate of 2-4 oz. per plant, spread evenly on the soil as far as the branches reach. This is applied when the buds begin to swell and again about 6 weeks later. The amount is increased an ounce a year until mature bushes are receiving half a pound at each application. Heavier applications may be needed to counteract the nitrogen starvation possibly induced by a sawdust mulch.
Pruning the Bushes
The Blueberry fruits on the wood of the previous season’s growth and the largest fruit is borne on the most vigorous wood. Blueberries that are unpruned usually overbear and produce small berries that may not ripen well and are of poor quality. Pruning, therefore, is necessary to reduce the crop to what the bush can mature and still produce vigorous shoot growth to fruit the following year. Light pruning tends to delay ripening, while heavy pruning hastens ripening, although reducing the crop. If one is producing early varieties for an early market, the pruning should be more severe than where late varieties are produced for a late market.
Little or no pruning is necessary until the end of the third growing season. Then the low weak shoots near the ground are removed and in dense bushes, the weaker growth in the center of the bush is thinned out. Older bushes will need more extensive pruning.
All of the suckers, or new shoots from the base, should be removed except as one or two may be needed to replace an old cane that is removed. Six or eight of the older canes are enough for mature bushes. Weak twiggy branches have few fruit buds and should be cut out. Vigorous fruiting wood of some varieties, especially Cabot and Pioneer, has too many fruit buds and the shoots should be cut back to 3-5 fruit buds per shoot. Injured and dead canes and branches near the ground should be removed. The pruner should try to do as much pruning as possible with a few large cuts as this is faster than many small cuts. Pruning may be done at any time after the leaves fall until the beginning of growth in the spring.
Harvesting the Crop
Several pickings are necessary and the interval between pickings is from 5-7 days. The berries keep very well on the plant, or in storage after picking, so that haste is not so essential as with other berries. The berries of some varieties color before they are ripe and care must be taken that only fully ripe berries are harvested for market. Immature berries, even though they are blue, are sour and lack the characteristic high flavor of a ripe Blueberry.
Improvement of Wild Blueberries
Good stands of wild Blueberries may be improved so that much heavier crops are produced than are borne by the uncared-for bushes. The first step is to cut out all trees and brush that compete with the Blueberry plants for light, moisture, and nutrients. The bushes should be pruned to remove dead wood, weak canes, and twiggy growth without many fruit buds. An application of sulfate of ammonia at the rate of a half-pound to a bush will stimulate vigorous new growth. This care will increase the crop, but not the size of the berries. To have large berries, one must plant the large-fruited varieties.
Managing the Low-bush Blueberry
The Low-bush Blueberry is native to the northeastern United States and adjacent Canada. In eastern Maine the extensive wild stands are managed according to a definite program. The plants grow only a few inches tall and spread by underground rhizomes. In the full sun they crop heavily, but among trees and brush little fruit is produced.
The fields are burned every two or three years to kill the weeds and underbrush and to prune the plants. Hay or straw with oil is used and the burning is done in the spring while the ground is still wet. Additional weeding may be done by pulling or with chemical weed killers, which must be used carefully to avoid injury to the Blueberry plants.
The crop is harvested with a special rake similar to a Cranberry scoop. The rake, which has many fingers, is run through the bushes and pulls off the berries, green as well as ripe. The berries are put through a winnowing machine to blow out the leaves and light dirt. The green and injured berries are removed as the fruit passes over a belt. Much of the crop is processed.
Birds are very fond of Blueberries and will often take most of the crop in home garden plantings. Scaring devices are of doubtful value and it is necessary to screen the plants with cheesecloth or wire netting if the grower expects to harvest much of the crop. In commercial plantings, there is enough fruit for both the birds and the grower and the loss is less noticeable.