Most succulents are readily increased by cuttings. Apart from mere multiplication of specimens, it is often possible to improve the shape of a weak or distorted plant by taking cuttings from it, for the removal of a part often promotes fresh growth; alternatively, the old plant can be replaced by the better-grown youngster. But the mere pleasure of rooting new plants so easily should not allow one to spoil a well-shaped plant, particularly if it is a cactus with a number of offsets attractively growing around it. Some people think it necessary to remove such offsets; but this is not so.
Choosing the Right Cutting Material
The parts of a plant which can be used vary according to the family.
Cacti and their offsets
Most cacti produce young plantlets or offsets; or branches can be used. With opuntias the pads, and with epiphyllums and other leaf-like cacti the stem-segments, are used. Wherever a stem is jointed, not less than one joint should be used. Columnar cacti can be beheaded and the top pieces rooted; those with long thin stems are cut up into suitable lengths. Clump-forming cacti can be separated. The tubercles of mammillarias and similar genera can be cut off and rooted, though usually enough offsets are produced.
Cactus-like succulents
Cactus-like succulents, such as many euphorbias and Stapelia and its relations, are treated in the same way, separating branches or offsets or beheading columnar stems. The latter method obviously ruins the parent plant, and is usually only resorted to when the base is damaged or has become woody, or the roots have decayed.
Leafy succulents and offset formers
Agaves, aloes, haworthias, gasterias, etc., produce easily removed offsets. Many kinds of Bryophyllum produce adventitious buds on the leaves, which make roots while still on the parent. Almost all succulents can be increased by stem cuttings, and most Crassulaceae by leaves as well. These are usually very easily detached, and if pushed into sandy compost, or even laid on its surface, root and produce new leaves around the base. Leaves of Aloe and Haworthia will also root. In fact, many succulents often put out roots if simply left lying in the air.
Aizoaceae and other difficult species
The Aizoaceae can be increased by stem cuttings; leaves will not root. The shrubby species root readily, but the fleshy ones are more difficult. Each pair of leaves, or plant-body in the highly succulent forms, can be treated as a cutting; the base of the plant must be undamaged.
When and How to Take Cuttings
Cuttings can be taken at any time, but late spring to high summer is best; at other times there is the danger of rotting due to damp and cold.
Ideal conditions for rooting
Bottom heat is helpful but not essential. If the pots or boxes can be watered from the bottom so much the better. Avoid a close atmosphere, which may provoke basal decay. It is advisable to provide shade from full sun.
Preparing the Compost and Rooting Medium
For rooting, the usual potting compost, with some extra grit, can be used, but pure coarse sand, or a mixture of sand and peat, is better; vermiculite, which holds moisture like the peat mixture, promotes very quick rooting. With all these the plants need to be potted up fairly soon after rooting, as no food is present. Perhaps the best method is to place the cuttings in a layer of coarse sand or vermiculite over the potting mixture.
The Importance of Drying and Callusing
The most important thing when taking cuttings of these plants is to dry them well.
Forming the callus properly
After making the cut, with a sharp knife or razor-blade, the cuttings must be left in a warm, dry place until a callus, or skin, has formed over the cut surface. With very fleshy cacti and some genera of the Aizoaceae, a period of several weeks may be needed. Never insert a cutting until the cut is well and truly dried, nor overwater the rooting material. The pieces to be rooted should not be pushed in at all deeply.
