When large numbers of plants are desired, as in commercial nurseries, it is often necessary to cut back the parent plant to the ground, or very nearly so, for the purpose of securing many shoots fit for layering. A plant which is cut back in the spring will produce shoots fit for layering the following spring; or some species will produce them in abundance the same year if layers of green or immature wood are desired. These parent or stock-plants are called “stools” by nurserymen.
Fig. 21. Mound Layering of Gooseberry.
In many species layerage is performed to best advantage by heaping earth over the stool and around the shoots. This is known as mound or stool layering. The shoots send out roots near the base and straight, stocky plants are obtained. The English gooseberries are almost exclusively propagated in this manner in this country. [Fig. 21] shows a row of mound-layered gooseberries. The shoots are allowed to remain in layerage two years, in the case of English gooseberries, if the best plants are wanted, but in many species the operation is completed in a single season. Quinces and Paradise apple stocks are extensively mound-layered. The practice is most useful in those low plants which produce short and rather stiff shoots.
As a rule, the best season for making layers is in spring when the leaves are forming. Rooting progresses rapidly at that season. Many plants “bleed” if layered earlier in the season. Hardy shrubs may be layered in the fall, either early or late, and if an incision is made, a callus will have formed by spring. If rapid multiplication is desired, the soft and growing shoots may be layered during the summer. This operation is variously known as “summer,” "herbaceous," “green” and “soft” layering. Comparatively feeble plants usually result from this practice, and it is not in common favor.
Fig. 22. Pot layerage.
Pot layering, circumposition, air layering and Chinese layering are terms applied to the rooting of rigid stems by means of surrounding them, while in their natural position, by earth or moss, or similar material. The stem is wounded—commonly girdled—and a divided pot or box is placed about it and filled with earth ([Fig. 22]). The roots start from above the girdle, and when they have filled the pot the stem is severed, headed back, and planted. Pot layering is practiced almost exclusively in greenhouses, where it is possible to keep the earth uniformly moist. But even there it is advisable to wrap the pot in moss to check evaporation from the soil. Some plants can be readily rooted by wrapping them with moss alone. Pot layering is employed not only for the purpose of multiplying plants, but in order to lower the heads of “leggy” or scraggly specimens. The pot is inserted at the required point upon the main stem, and after roots have formed abundantly the top may be cut off and potted independently, the old stump being discarded.