PROPAGATION OF ALPINE PLANTS: DIFFERENT METHODS
There are three methods of propagating alpine plants and these are very similar to those used for other garden plants. They are: (a) raising from the seed which many alpines produce in copious quantities; (b) increasing by lifting and dividing old plants; (c) rooting frommade from soft growth tips, either before or after the plants have flowered.
Those which are true species may be expected to reproduce themselves true to type from seeds, but named garden forms or hybrids are less likely to do so. Most hybrids are sterile, that is, they do not set seed, but some are occasionally fertile. From these and selected forms, considerable variation must be expected among the, so that in the case of a hybrid it is best to rely on vegetative methods of propagation, such as cuttings, which ensure that the increase will be the same as the plants from which they were raised.
Example: Aubrieta is a good example of the type of plant which does not come true from seed. It is easy to obtain seed of good strains of aubrieta, and if particular colours are not desired, this is an easy and inexpensive way of obtaining a useful stock of these decorative spring-flowering plants. The best aubrietas, however, are the named varieties, of which there are a couple of score or more. These may be increased by division or by cuttings.
Division is the simplest method of vegetative propagation. In general, the best time to lift and divide a plant is just after it has flowered. Having completed its annual cycle of growth and fulfilled its purpose by blossoming, the plant is about to begin all over again by producing new roots and building up strength to repeat the display the following year. Carefully lift the plant from moistenedand shake or wash as much as possible of the soil from its roots. Cut back the top growth and gently break the plant into as many pieces with individual roots as it will provide.
These separate plants will establish more quickly if potted into a fairly sandy, put in a closed frame for a week to ten days, and kept constantly moist but not saturated. During this time the plants will be making new roots, so the frame should not be too freely ventilated until they have formed a firm root ball. They may then be planted out, or retained in their pots until it is convenient to plant them into permanent places.
If it is not possible to pot the divided plants, plant them immediately into their permanent positions, keeping the plants moist and shaded for a week or two afterwards. Their recovery will not be as rapid as that of separately potted plants, but there is little risk of loss among the more ordinary and easily-grown plants.
Do not treat rarities in this manner; always pot them.
Offsets: Many alpine plants can be easily propagated by detaching pieces which have formed roots and treating them as separate plants, either potting them or planting them directly into new positions. Among the kinds which lend themselves to this easy method are all the alpine phloxes, many dwarf veronicas and all the creeping thymes — in fact, all those that spread by procumbent stems which root as they go along the ground.
Some alpine plants cannot be divided, as they tend to grow with one single, in-divisible neck, or crown, from which radiate upright or procumbent stems. These plants can be increased by making nodal cuttings of the soft tips of new shoots.
How to make a nodal cutting: Trim off the lower leaves from the shoots with a very sharp knife or old razor blade and make a clean cut exactly beneath a leaf-joint or node, leaving a short, bare stem. Insert this stem in pure sand, or sand with a very little finely granulated peat. Builders’ yellow sand is useless: use a sharp gritty sand which will not bind. Place the cuttings firmly and closely together in small pots or pans and keep them in a closed and shaded frame until they begin to root. Then ventilate them until they are sufficiently well rooted to be potted off separately. If a frame is not available, put the pots in a fairly deep box, covered with a sheet of glass, in a shady position and treat it as a miniature frame.
Which shoots to choose: When selecting shoots to be made into cuttings avoid any which have flower buds, as they will not make good cuttings. They may root, but will seldom grow into bushy, healthy plants. Whenof violas or pansies, do not use any which have hollow stems as they will not root.
Stopping: A few days after the cuttings have rooted and have been separately potted, nip out the tips of the plants. This will induce them to break from below into branching, bushy specimens. Plants which are not so stopped often form weak, spindly plants with no more than one or two frail stems.
Root cuttings: Several plants, among them Morisia monantha (syn. M. hypogaea), produce very little seed and do not divide readily, but they can usually be increased by. To encourage the formation of the right kind of roots, lift a plant the year before it is to be propagated and pot it ‘into a very deep pot, or even into a three-inch drain pipe, using light, sandy soil.
This encourages the formation of long, thong roots, which can be detached in the spring, cut into approximately inch lengths and laid flat on a surface of pure sand in a box or pan, and lightly covered with sand. Keep them moist and shaded in a close frame and these small pieces of root will quickly sprout and form vigorous young plants, which can be potted and grown in the same way as normal cuttings.