Plants can be propagated from seed, from cuttings, division, from suckers and layers, and by grafting. This articles describes division and layering method of propagation.
This method of propagation applies to suckering shrubs, tuberous-rooted plants, rhizomes and bulbs. Division is usually carried out between October and April. The rhizomes of Irises and similar plants are divided by a cut from a sharp knife. Tubers of Begonias and Potatoes are divided by being cut up, whereas those of Dahlias, which are root tubers, are split in such a way that each portion carries a sliver of stem from which a new plant will grow.
Another form of division applies to bulbs and corms. Here, when they are lifted, small bulbils or cormlets will be found attached to the parent bulb. Detach these and plant them out in a nursery bed, where after about two years they will start to flower. Some Lilies grow bulbils in their leaf axils. Collect these in late summer and plant them 1.25 cm deep and 3.7 cm apart in compost in a deep box. After three years they will be flowering size.
Propagation by suckers is another form of division, undertaken in autumn. Sever rooted suckers of trees and shrubs, growing on their own roots, with a sharp spade, close to the parent. Lift them out and plant in a nursery bed, until the following autumn, when they can be planted in their permanent positions.
Most trees and shrubs, with low-growing, pendulous branches can be propagated by layering. Forsythia suspensa, Lilacs, Heathers, Magnolia and Willows are especially amenable to this method.
Select a young, non-flowering, flexible shoot and pull it to the ground. This can be done at any time, but the best period is from September to November.
At the point where it touches the ground make an incision in the stems, so that a small tongue opens up when the shoot is bent. This obstructs the flow of the sap. Apply hormone rooting powder to the wound. Cover this point lightly with soil and firm in, holding the growing tip upwards, and then attach it to a small cane. Secure the bend by means of a U-shaped pin.
After about 12 months (up to two years for Magnolia and Rhododendrons), roots will form and the new plant can be severed from its parent and either potted up or planted out. Although grafting is possible, the technique is confined to professional use, except for fruits.