The larger shrubs, as lilacs and syringas, may be set about 4 feet apart; but the smaller ones should be set about 2 feet apart if it is desired to secure an immediate effect. If after a few years the mass becomes too crowded, some of the specimens may be removed (*p. 76).
Throw the shrubs into an irregular plantation, not in rows, and make the inner edge of the mass more or less undulating and broken.
It is a good practice to mulch the plantation each fall with light manure, leaf mold, or other material. Even though the shrubs are perfectly hardy, this mulch greatly improves the land and promotes growth. After the shrub borders have become two or three years old, the drifting leaves of fall will be caught therein and will be held as a mulch (p. 82).
When the shrubs are first planted, they are headed back one half or more (Fig. 45); but after they are established they are not to be sheared, but allowed to take their own way, and after a few years the outermost ones will droop and meet the green*-sward (*pp. 25, 26).
Many rapid-growing trees may be utilized as shrubs by cutting them off near the ground every year, or every other year, and allowing young shoots to grow. Basswood, black ash, some of the maples, tulip tree, mulberry, ailanthus, paulownia, magnolias, Acer campestre, and others may be treated in this way (Fig. 50).
Nearly all shrubs bloom in spring or early summer. If kinds blooming late in summer or in fall are desired, they maybe looked for in baccharis, caryopteris, cephalanthus, clethra, hamamelis, hibiscus, hydrangea, hypericum, lespedeza, rhus (R. Cotinus), Sambucus Canadensis in midsummer, tamarisk.
Plants that bloom in very early spring (not mentioning such as birches, alders, and hazels) may be found in amelanchier, cydonia, daphne, dirca, forsythia, cercis (in tree list), benzoin, lonicera (L. fragrantissima), salix (S. discolor and other pussy willows), shepherdia.
Shrubs bearing conspicuous berries, pods, and the like, that persist in fall or winter may be found in the genera berberis (particularly B. Thunbergii), colutea, corylus, cratægus, euonymus, ilex, physocarpus, ostrya, ptelea, pyracantha (Plate XIX) pyrus, rhodotypos, rosa (R. rugosa), staphylea, symphoricarpus, viburnum, xanthoceras.
List of shrubbery plants for the North.
The following list of shrubs (of course not complete) comprises a selection with particular reference to southern Michigan and central New York, where the mercury sometimes falls to fifteen degrees below zero. Application is also made to Canada by designating species that have been found to be hardy at Ottawa.