The fact is well appreciated that of all our great range of material used in landscape plantings there are a certain number of these species and varieties which are better adapted to being transplanted at some specific season, either during the spring or during the fall. It is generally safe to assume that plants such as the poplars, willows, and the rose of Sharon, the wood of which is late in ripening, should preferably be transplanted in the spring. If these types are transplanted in the fall, they are, during a normal severe winter, subjected to a considerable winter-killing, and must be severely cut back in the early spring; whereas, if planted in the spring they almost invariably continue to grow and require little or no cutting back.
The group of perennials which should not be transplanted in the spring consists mostly of those plants which begin their growth at the first sign of spring, and before the ground is really in fit condition to "work." These plants, by the time the ground is warm and dry enough to permit transplanting in friable soil, have developed so much growth of roots or of both roots and top, that unless they can be immediately moved without any period of delay from their existing location to a new location they should by all means be transplanted during the fall. If such plants are transplanted in the spring the usual result is a check to growth and exceptionally weak development of flowers and of foliage during that season. The fall transplanting of perennials ought to be done, especially with these early spring-flowering types, during September rather than during the latter part of October and November, when the ground is cold and growth is completely stopped. Transplanting earlier in the fall enables the plants to start some root growth and thus to establish themselves to better withstand the winter conditions, especially in the soils containing more or less clay. Especially should the peony, for any degree of success, be trans planted in the fall. The iris is peculiar and can be successfully transplanted at any time when the ground is not frozen. The best time is believed to be immediately after flowering.
Plate XLIV. The large garden rilled with perennials usually consists of larger groups of flowering perennials which produce masses of colour during their period of bloom. Iris, phlox, hollyhocks, gladioli, larkspur and anemone produce the more important flower effects in this garden. (See Chapter XXXI (Perennials For Different Purposes))
Plate XLV. A cut-flower garden; the central part filled with annuals and the outer border of perennials serving as a frame with shrubs in the extreme background. A garden of this kind can have a succession of bloom throughout the flowering season. (See chapter XXXII (Annuals))
Plants which are not vigorous in their habit of root growth and which are very susceptible to abnormal conditions of freezing and thawing, or to excessive moisture in the soil during the winter months, should not be transplanted in the autumn. The most important illustrations of this type of plants are the beech, the flowering dogwood, and some of the less hardy types of evergreens, such as the arborvitae and the pea-fruited cypress. Many good plantsmen are of the opinion that rhododendrons and azaleas should be planted during the spring months. As is the case with the refined types of evergreens, there is usually less loss from spring planting of this material than from fall planting. The question of period of transplanting in connection with rhododendrons and with evergreens has been discussed under the chapter on Planting and Transplanting (Page 49).
While it is desirable in the transplanting of evergreens and of rhododendrons in particular to move them at a time when they are just ready to begin growth, in order to prevent them from standing in a "cold soil," it is, on the other hand, necessary to transplant such trees as the beech and the birch when they are absolutely dormant. If they have shown the least signs of growth through the swelling of the buds, the operation of transplanting becomes more difficult, and yet to transplant such material in the fall and to permit it to stand through the winter, especially in a heavy soil, subjects it to the possibility of considerable loss. There is a well-defined group of perennials, typical of which are the chrysanthemum and the Japanese anemone, which can seldom be transplanted with any success during the fall season. The reason for this is that the plant produces flowers at such a late period in the growing season that further root action necessary to establish the plant in a new location and successfully carry it through the winter is not encouraged.
Group C includes plants divided into two sub-groups, a those which transplant with difficulty and should rarely if ever be transplanted, but grown in their permanent location from seed, cuttings, or very small seedlings, and b those which after being transplanted recover very slowly. All of the plants in the first group are the extremely slow-growing types, such as the walnut, the butternut, the ironwood, and the sweet fern. Those typical of the second groups are the Japanese snowball, the rose of Sharon, boxwood, nursery-grown beech trees, and sweet gum. The author does not intend to convey the impression that any of the plants in either of these groups, especially the first group, cannot be transplanted with success by those who are in a position to know the plants intimately, and to take thorough precautions against any possible injury through transplanting. For the person who is not an expert plantsman and who does not thoroughly understand all of the conditions necessary for the successful transplanting of the extremely slow-growing types of trees and shrubs the plants in the first group should be avoided, and extreme care should be given to the work of transplanting any of the trees or shrubs included in the second group.
Most of the plants included in the second group should be transplanted for best success during the spring months. Their habit of slow growth and inability to adapt themselves readily to new conditions of soil make them very liable to injury on account of drowning-out because of excessive depth of planting, or injury from winter conditions. All of these types are apt to be extremely unsatisfactory during the first two years after transplanting, but when once they have recovered from the shock of transplanting they will grow wonderfully well.