Propagation of Garden Plants

Since a true garden lover will gain great satisfaction from growing his or her own plants from seed or cuttings, we shall deal with this subject in some detail. In many cases it is surprisingly easy. Plants not normally commercially available can be raised from cuttings, seed, by grafting or by division. Most gardeners enjoy sharing their plants.

From seed

The most usual method of propagation is by sowing. Many people think that only annuals can be grown from seed, but numerous perennials, shrubs, conifers, bulbous and tuberous plants can also be successfully raised by this method. The choice of seeds available in this country is enormous, but they may also be obtained from all over the world as, unlike plants, seed is rarely subject to problems of inspection and import control.

Sowing from a seed strip

Sowing from a seed strip (above) and in drills filled with seed compost (below)

drills filled with seed

Seed compost

It is advisable to use special seed compost, in which the seeds will germinate more easily. For many plants a mixture of potting soil and sharp sand in equal amounts is excellent. Seeds left for a long time (out of doors) are kept in pure sharp sand.

Germination

Some seeds germinate better in high temperatures and are raised in warm conditions. On the other hand some seeds require a period of frost, after which they will germinate at a low temperature, for instance primulas. Shrub seed must often be kept throughout the winter in cool, but frost-free, damp sand, after which it will germinate in spring. As a rule the correct method of sowing can be found on seed packets.

Sowing

It is convenient to use flat, plastic trays with drainage holes for the desired seeding compost. Fine seed must be scattered thinly. Cover with sifted potting soil or sharp sand. The trays may then be placed directly in a warm position (window-sill, greenhouse or heated frame), or can first be kept in the refrigerator or even the freezer for a time.

Pricking out

As soon as the seedlings have developed their second pair of leaves, or in the case of monocotyledons when they are 5 cm tall, they must priced our. They may be put in plastic, clay or peat pots or planted out in the garden. In most cases the pots may be filled with ordinary potting soil. It is often necessary to grow the pricked out plants under glass for a time, and if they have been sown early in spring they must not become too cold. At a later stage the plantlets are gradually acclimatised to drier and cooler air; this process is called hardening off.

Sowing out of doors

Many types of seed may be sown out of doors. The seed-bed should preferably have a certain amount of shade, especially in the case of biennials, which are sown out of doors early summer. Improve the soil with peat fibre or potting soil, so that it will retain moisture; this will encourage germination. Always sow in rows, since otherwise you will be unable to distinguish the seedlings from weeds appearing at the same time. At a later stage the seedlings are thinned out to the desired distance.

Layering

Various shrubs with supple twigs can be increased by layering. In the autumn a

1 year-old twig is bent down until it touches the soil; a small cut is made in the wood, kept open with a little pebble. The wound is covered with soil and pegged down. After a year roots will have developed and the offset can be lifted.

Taking cuttings

how to take winter cuttings

Above: winter cuttings Below: summer cuttings

how to take summer cuttings

In the case of many perennials cuttings may be taken in spring, summer or autumn, depending on the species. As a rule shoots are used for this purpose, but occasionally root cuttings are taken instead.

The medium prescribed for sowing is usually satisfactory for growing cuttings as well. Sometimes it is advisable to add extra sand. Additional heat may encourage rooting, and cuttings are often dipped in rooting powder for the same reason. To avoid evaporation via the leaves, cuttings are frequently kept under glass or plastic. Cuttings are taken just below a growth bud, from which the roots will develop. Woody cuttings often root more readily if taken with a heel, ie a strip of bark. Cuttings from tuberous plants may be taken in spring and grown under glass. They are taken after shoots have appeared; often a piece of tuber is left attached.

In the case of lilies and a number of other bulbous plants, the bulb scales may be used as cuttings. This is done in the autumn; the bulbs are peeled and the scales are kept in trays filled with a, cutting medium, at a temperature of 20- 25°C.

There are two different methods for taking cuttings from shrubs: summer cuttings and winter cuttings. The former are taken from that year’s shoots, and many deciduous and evergreen shrubs and conifers are increased by this method. The cuttings are 5-15 cm long, cut just below a growing point, often with a heel. As a rule they are dipped in rooting powder. Summer cuttings are usually grown under glass; if they do not root easily (conifers, rhododendrons), they are grown under fine spray. Small misting apparatuses for amateur gardeners are available from greenhouse suppliers. Often it is necessary to provide bottom heat to induce the cuttings to root in good time. Summer cuttings must be kept fairly cool in the first winter, but definitely frost free. They may be moved out of doors in the following spring. Taking winter cuttings from shrubs is an even simpler operation, and is frequently done in the case of shrubs with thick, strong shoots. In mid-autumn 1 year-old twigs are cut into 10-20 cm sections, which are buried out of doors in sharp sand. The sand must be kept moist but frost-free throughout the winter. A callus layer will develop on the cut surface; this can grow roots in spring. After this the cuttings are kept in a seed-bed for a further year.

Division

Many perennials and a number of small shrubs are easily propagated by division. This is best done in spring, although it is also possible in early autumn, provided the plants have died down sufficiently (eg irises, peonies).

When a plant is divided the centre part, which by then has lost vigour, is usually discarded and the outer sections are used for propagation. These may be grown in a separate bed to start with, or be returned to the border.

Bulbous plants are also easily divided. The operation is simpler if the bulbs are first allowed to sprout a little. Make sure that each section bears at least one shoot. The cut sections are allowed to dry out a little before being planted.

dividing a perennial by hand

Dividing a perennial by hand (above) or with a spade (below).

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Grafting

This slightly more difficult method of propagation consists of uniting two (different) plants by pressing their growing tissue together. It is often done in the case of shrubs with weak roots; a strong root system is used as stock, a choice shrub produces the scion. The scion is usually cut in autumn and kept in a cool place, to be united with the stock in spring.

In whip grafting, stock and scion are of equal thickness. They are both cut at a slant and tied together with raffia. Initially the stock retains some foliage.

In the method called rind grafting, the stock is much thicker than the scion. The scion is cut in the shape of a triangle and inserted under the bark of the stock. Several scions can be placed side by side. They are tied with raffia and the joint is covered with grafting wax.

Budding is a special method of grafting, in which only a growing point is inserted in the incision in the stock. This is done in mid summer and is especially applicable in the case of roses. It is a finicky job. Watch a professional at work; after a little practice you will be able to do it yourself. Its greatest advantage is that it enables one to obtain rare strains, simply by taking a flowering shoot.

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