|Standard Cyclopedia of Horticulture|
Blueberry-Culture. Fig. 586. Blueberries are fruit-bearing shrubs of the genus Vaccinium, long gathered wild in North America in great quantities and now about to be cultivated with success. Success in blueberry-culture rests especially on the recognition of two peculiarities in the nutrition of these plants: first, their requirement of an acid soil; second, their possession of a root-fungus that appears to have the beneficial function of supplying them with nitrogen.
If blueberries are planted in a soil with an alkaline or neutral reaction, such as the ordinary rich garden or fertile field, it is useless to expect their successful growth. In such a situation they become feeble and finally die. Blueberries require an acid soil, and they thrive best in that particular type of acid soil which consists of a mixture of pure sand and peat. The peat may be of either the bog or the upland sort.
Good aeration of the soil is another essential. It is commonly but erroneously supposed that the swamp blueberry (Vaccinium corymbosum), the species chiefly desirable for cultivation, grows best in a permanently wet soil. It is to be observed, however, that the wild plants of the swamps occupy situations which though perhaps submerged in winter and spring are exposed during the root-forming period of summer and autumn, or, when growing in permanently submerged places, they build up a hummock or a cushion of moss which rises above the summer water-level and within which the feeding-roots of the bush are closely interlaced. In actual culture, moreover, it has been found that the swamp blueberry does not thrive in a permanently wet or soggy soil.
Although some species of Vaccinium, such as the common low-bush blueberry, V. pennsylvanicum, grow and fruit abundantly in sandy uplands that are subject to drought, the swamp blueberry grows best in soils naturally or artificially supplied with adequate moisture.
These then are the three fundamental requirements of successful blueberry culture: (1) An acid soil, especially one composed of peat and sand; (2) good drainage and thorough aeration of the surface soil; and (3) permanent but moderate soil-moisture. Under such conditions, the beneficial root-fungus which is believed to be essential to the nutrition of the plant need give the cultivator no concern, for it will propagate itself spontaneously and adequately, without any necessity of soil or plant inoculation.
Blueberry plantations may be formed by the transplanting of unselected wild bushes or by the growing of seedlings, but such a course is not the best. Seedling plants, even from the largest-berried parents, produce email berries oftener than large ones. Until nurserymen are prepared to furnish plants asexually propagated from superior stocks, the cultivator should begin by the transplanting of the best wild bushes, selected when in fruit for the size, color, flavor, and earliness of the berry, and the vigor and productiveness of the bush. These he should propagate by layering and by cuttings until his plantation is completed. By means of a combination of these two methods, a valuable old plant can be multiplied by several hundred at one propagation, the fruit of the progeny retaining all the characteristics of the parent.
Large berries cost less to pick than small ones and bring a higher price. A berry H of on inch in diameter has already been produced under cultivation and others of still larger size are to be expected.
While grafting and especially budding are useful in experimental work, neither method is suitable for commercial plantations because blueberry bushes are continually sending up new and undesirable shoots from the stock. The best season for budding is from the middle of July to the end of August. The budded plants should be protected from direct sunlight, and special care should be taken that the raffia wrapping does not become wet for the first three weeks.
The easiest way to propagate the swamp blueberry is by a special process of layering known as "stumping." In early spring, preferably before the buds have begun to push, all the stems of the plant, or as many as it is desired to sacrifice for propagation, are cut off close to the surface of the ground. The stumps are then covered to the depth of 2 inches with a mixture of about four parts of clean sand and one of sifted peat. The sand- bed must not be allowed to become dry, except at the very surface. The new growth from the stumps, which without the sand would consist of stems merely, is transformed in working its way through the sand into scaly, erect or nearly erect rootstocks which on reaching the surface continue their development into leafy shoots. Although roots are formed only sparingly on the covered bases of stems, they develop quickly and abundantly on these artificially produced rootstocks. By the end of autumn the shoots are well rooted at the base. They should remain in place in the sand-bed through the winter, exposed to freezing temperatures. Early in the following spring, before the buds have begun to push, each rooted shoot is carefully severed from the stump. The upper portion of the shoot is discarded, the cut being made at such a point as to leave on the basal portion about three buds above the former level of the sand-bed. The rooted shoots are potted in clean 3-inch porous pots in a soil consisting of two parts of rotted upland peat to one of sand and one of clean broken crocks. They are then plunged in sand in a shaded coldframe or greenhouse, with abundant light but no direct sunlight. For the first two months the temperature should be kept below 65° F. When subjected to high temperatures, the newly cut shoots are liable to die and rot from the base upward. Watering should be infrequent, only sufficient to keep the soil moist but well aerated. The frame should receive ventilation but not enough to cause the new twigs to droop. They are very susceptible to over-ventilation and overheating just before they complete their primary growth. After the new twigs have stopped growing and their wood becomes hard, new root-growth takes place. Then secondary twig-growth follows. Not until this has occurred is the life of the plant assured. Those plants that make sufficient growth to require repotting during the first summer should be transferred to clean pots of 2 inches larger diameter in a standard blueberry soil mixture.
A very successful potting mixture, or nursery-bed mixture, for blueberry plants consists of one part of clean or washed sand, nine parts of rotted upland peat, either chopped or rubbed through a sieve, and three parts of clean broken crocks. No loam and especially no lime should be used.
Manure is not necessary, and in the present state of our knowledge may be regarded as dangerous, although in small amounts it serves to stimulate the plants, at least temporarily. The danger from manure apparently lies in its tendency to produce an alkaline condition in the soil.
The use of crocks in the potting mixture is based on the fact that the rootlets seek them and form around them the same mats that they form at the wall of the pot, thus increasing the effective root-surface and the vigor of growth.
The peat most successfully used for potting blueberry plants is an upland peat procured in kalmia, or laurel, thickets. In a sandy soil in which the leaves of these bushes and of the oak trees with which they usually grow have accumulated and rotted for many years untouched by fire, a mass of rich leaf-peat is formed, interlaced by the superficial rootlets of the oak and laurel into tough mats or turfs, commonly 2 to 4 inches in thickness. These turfs, ripped from the soil and rotted from two to six months in a moist but well aerated stack, make an ideal blueberry peat. A good substitute is found in similar turfs formed in sandy oak woods having an underbrush of other ericaceous plants than laurel. Oak leaves raked, stacked, and rotted for about eighteen months without lime or manure are also good. The leaves of some trees, such as maples, rot so rapidly that within a year they may have passed from the acid condition necessary for the formation of good peat to the alkaline stage of decomposition, which is ital to blueberry plants. Even oak leaves rotted for several years become alkaline if they are protected from the addition of new leaves bearing fresh charges of acidity.
By ordinary methods, cuttings of the swamp blueberry have been rooted only in occasional instances. Two successful methods, however, have been especially devised for these plants. The most novel of these but the one easiest of operation is that of "tubering." This method involves the same principle as that employed in stumping, namely the forcing of new shoots in such a manner that their basal portions are morphologically scaly rootstocks, with a strong rooting tendency. This method of propagation from stem cuttings is called tubering because the treatment as well as the behavior of the cuttings is essentially identical with that which takes place in reproduction from tubers, as in the case of the potato.
The cuttings are made in late winter or early spring, and the whole plant may be used, including old stems an inch or more in diameter. With a saw and knife cut the wood in pieces about 4 inches long. Lay these horizontally in a shallow, well-drained box containing a bed of clean sand and cover them with half an inch of the same material. Water the sand well, cover the box with glass, and keep it at a temperature of 60° to 65°, or less if the equipment does not permit the maintenance of such a temperature. The sand-bed must be kept moist, although if there are only slight apertures beneath the glass, a second watering may not be required for several weeks.
At the temperature already specified, shoots should begin to appear above the sand within six weeks. The boxes should then be placed in good light but protected from direct sunlight, and, when warm weather approaches, they should be given the coolest situation available so as to keep the temperature below 65° as long as practicable. When the first shoots have stopped growing and their foliage has turned to a mature green color, they are ready to produce roots. A half-inch layer of finely sifted rotted peat should then be added to the surface of the sand-bed and thoroughly wet down with a fine spray. The box should remain in this condition, with a little ventilation but a saturated or nearly saturated atmosphere, until new shoots cease to appear. Meanwhile, during the spring and early summer the older shoots will have formed roots between the surface of the ground and the point at which they sprang from the cutting. After a shoot is well rooted it will make secondary twig-growth, and if the development of roots has not already been ascertained by direct examination, the making of such secondary growth is good evidence that rooting has actually taken place. If the rooted shoots have not already disconnected themselves from the dead cuttings they should be carefully severed with a sharp knife. They are then potted in 2-inch pots in the standard blueberry soil mixture already described, and during a period of three or four weeks they should be gradually changed from their saturated atmosphere and full shade to open air and half sunlight. If preferred, the shoots may remain in the original cutting-bed until the following spring, before potting, the cutting-bed being exposed to freezing temperatures during the winter.
When blueberry plants, either large or small, are grown in porous pots, the surface of the pot should never be allowed to become dry, for the rootlets, which grow through the soil to the wall of the pot for air, are exceedingly fine and easily killed by drying, to the great injury of the plant. This danger may be eliminated by plunging the pots to the rim in a well-drained bed of sand, or by setting the pot in another pot of 2 to 4 inches greater diameter, with a packing of moist sphagnum between, and crocks at the bottom.
A burning of the young leaves and growing tips of twigs is often produced by the hot sun from the middle of June to the middle of September. Plants in pots or nursery beds arc easily protected from such injury and forced to their maximum growth by a half-shade covering of sluts, the slats and the spaces between being of the same width. On cloudy days the shade should be removed. It should not be used in fall or spring.
During the winter the rooted cuttings or one-year- old plants should be kept outdoors, exposed to freezing temperatures, their soil mulched with leaves, preferably oak leaves. When kept in a warm greenhouse during the winter they make no growth before spring. Even then their growth is abnormal, often feeble, or sometimes deferred for a whole year.
Plants from cuttings or rooted shoots are ready for permanent field planting when they are two or three years old and about 1½ to 2 feet high. They are best set out in early spring before the buds have begun to push.
The field plantation.
It is a curious fact that these plants send put no new roots in spring until they are in full leaf, their flowering is nearly or quite finished, and their principal twig- growth has ceased. It is important, therefore, in taking up either a wild or a cultivated plant from the open ground, that as much as possible of the old root-mat be lifted with the plant, for upon this they depend for moisture until their new rootlets are formed.
In the case of mature wild bushes with very large root-systems, when it is practicable to secure but a fraction of the root-mat, say a disk only 3 or 4 feet in diameter, it is the best procedure to cut all the stems to the ground at the time of transplanting. The bush will then produce a new and symmetrical top of a size suited to the capacity of the roots. The wood that is removed may be used for cuttings if the plant is sufficiently valuable.
A plant pollinated with its own pollen, or with pollen from its asexual offspring, produces fewer, smaller, and later berries than a cross-pollinated plant. In a field of plants propagated from cuttings or layers, two parent stocks should be used, a row of plants from one stock being followed by a row from the other.
In the permanent field plantation the bushes should be set 8 feet apart each way. When they reach mature size they will nearly or quite cover the intervening spaces.
To secure full vigor of growth, the ground between the bushes must be kept free from all other vegetation. On rocky uplands a continuous mulch of oak leaves, when it is practicable to secure them, will help toward this end as well as keep the soil in the necessary acid condition. It is more economical, however, to choose such a location for the plantation as will permit the use of horse-drawn machinery, and will make mulching unnecessary.
The most favorable location for blueberry-culture is a boggy area with a peat covering and sand subsoil, the peat preferably of such a thickness that a deep plowing will turn up some of the underlying sand.
The land should be so ditched that the water-level can be kept at least a foot below the surface of the ground during the growing season or can be raised for subirrigation during a drought.
The ground should be plowed to the depth of about 8 inches and repeatedly narrowed during the season preceding the planting, in order to kill the vegetation. After the plants are old enough to have formed a root-mat, the harrowing should be very shallow, not more than 2 or 3 inches, so that the roots will not be injured.
By proper manipulation in the greenhouse, seedling blueberry plants can often be made to ripen a few berries in less than a year, but they do not come into commercial bearing in field plantations until they are about five years old, when the plants are 3 to 4 feet high. They then increase slowly to full size and full bearing.
The field plantings resulting from the recent experiments in blueberry culture arc too young to show the mature yield. Fortunately, however, there has been found, near Elkhart, Indiana, a small blueberry plant ing of mature age, believed to be the only commercial plantation in existence, which sets forward our knowledge of yields by at least a decade. The plantation is a little less than two and a half acres in extent. It was started in 1889 in a natural blueberry bog, which was first drained and then set with unselected wild blueberry bushes. Exact records of yield and receipts are available only for the years 1910 to 1912. They are as follows:
Year Yield Qts. Price (approx. avg. per qt.) Receipts
1910 (a year of "almost total HMD 17⅛ cts. $178 25 failure" because of late spring freezes)
1911 5620 12⅞ cts. 725 25
1912 5900 12⅞ cts. 758 25
The annual expenses for weeding, cultivation, and irrigation were about $50. The cost of picking was 5 cents a quart. The general cost of maintenance of the equipment was about $5 per year, the crates and boxes being used repeatedly.
Estimating an annual charge of $30 for interest, $5 for taxes, and $10 for depreciation, the profits for these three years are computed as follows:
Year Profits per acre
1911 . 139
1912 . 147
It must be borne in mind that these figures are based on the yields from wild bushes transplanted without selection as to individual productiveness or the size of the berries. With bushes propagated from selected stocks, the yield should be greater and the berries much larger, this greater size probably effecting a reduction in the cost of picking and certainly an increase in the selling price.