Propagating Plants – Methods of Plant Propagation


Methods of Plant Propagation

Shrub Care and Propagating Plants

Immediately after planting, damaged branches or shoots should be cut away making the cut immediately above a bud. Contrary to the beliefs held by many gardeners, many shrubs need little or no pruning at all. Certainly they do not need an annual hacking back in the winter or spring, an operation often carried out for the sake of ‘tidiness’ rather than to help the plant to produce more and better flowers or fruits, which should be the object of pruning.

Where shrubs make reasonably symmetrical specimens in the normal course of events, there is no reason why the occasional ‘wild’ shoot should not be cut back, but this, like the removal of dead or dying shoots, is a mere tidying operation rather than real pruning.

Basically, shrubs may be divided into three groups:

  • those that need no pruning;
  • those that produce flowers in the spring on shoots made during the previous year;
  • and those that flower in summer or autumn on shoots made in the current season.

Those that flower on the previous season’s growths should be pruned after the flowers have faded, cutting back those shoots that have borne flowers. Those that flower on the current season’s wood are usually pruned the following spring, cutting back the old growths that flowered the previous year to within a few inches of the point where they spring from the main stem.

Many shrubs and trees, especially rhododendrons, azaleas, magnolias and camellias, benefit from an annual mulch in spring of such materials as moist peat, rotted compost or leaf-mould. The mulch should be spread over the soil round the shrub to a depth of several inches. It will gradually be absorbed into the soil by the action of worms or washed into the soil by rain. Any left on the surface in the autumn may be lightly forked into the top few inches of soil, taking care to avoid damage to roots near the surface.


Methods of Propagating Plants

There are several methods of plant propagation when it comes to shrubs, although not all of them can be relied upon to give good results. It is, for instance, possible to grow many shrubs from seed, though it can be a slow process. The seeds of trees, paeonies, for example, may take a year or even two years to germinate. Germination of hard-coated seeds can be hastened by stratifying them. This consists of exposing them to the action of frost and weather to help to break down the hard outer coating. The method often adopted is to place, in the autumn, a layer of sand in a flower pot or seed pan, put in a layer of seeds, add another layer of sand, another layer of seeds, until the pot or other container is full and then leave this outdoors all winter in an exposed place. By the following spring the seed coats should have rotted or partially decomposed and it is then possible to sift out the seeds from the sand and sow them. This can be done in pots of seed compost in a cold frame or cold greenhouse, or outdoors, when germination should be quite rapid.


Taking Cuttings

Propagating plants by cuttings is not difficult. Cuttings of half-ripe growths may be taken in summer, and rooted in a closed propagating case in the greenhouse, in a mixture of moist sand and peat or even in pure sand. If pure sand is used the cuttings must be potted into a soil mixture as soon as roots have formed. They are then grown in pots, until they can be planted out into a nursery bed the following spring and into their permanent place the following year.

Propagation by hard-wood or naked cuttings is successful with many shrubs. These are taken in October or November and are usually 6-12 inches long. As with most cuttings, the shoots are trimmed just below a joint or bud, the lower leaves, if any remain, are removed, and the cuttings are inserted 3-4 inches deep, either in pots of sandy compost placed in a we1l-ventilated cold frame, or out of doors, in a sheltered position. Out of doors it is usual to make a slit in the ground with a spade, scatter sharp sand in the bottom, insert the cuttings and then firm the soil around them. By the following spring they can be lifted carefully and planted out, spaced 6-12 inches apart in a nursery bed. If evergreens are to be propagated in this way it is better to root them in a cold frame. Hormone rooting powders are available, but few gardeners require more than a small number of extra specimens and it is quite usual to expect a 50% ‘strike’ and not at all unusual to find that 90% of cuttings of certain shrubs have rooted.


Layering

Some shrubs are easily increased by layering their shoots. Some will even layer themselves as long shoots touch the ground and root from the point of contact. Shoots, preferably those that can easily be bent down to ground level, can be buried in the soil and, from the buds or nodes below soil level, roots should form. The rooted layer can eventually be cut off from the parent plant and start an existence of its own. With some shrubs all that is required is a long shoot bent down, buried in the soil and a stone or wire peg used to hold it in position. Success is more often assured, however, if the woody shoot is slit just below a joint, to form a ‘tongue’ at the point where it is buried in the soil. Alternatively, when the shoot is bent down it can be twisted and bent up-wards at this point and then buried and held in place. On heavy soils it is advisable to provide a good rooting medium, such as a mixture of sand and peat, at the rooting place. A brick or stone, placed over the point where the stem is buried, is probably considerably better than a wire peg, because the soil beneath the brick will then remain moist, even in dry weather.


Division

Hypericum calcyinum Division is a method of plant propagation often used where herbaceous perennials are concerned but is applicable to only a few shrubs, those that make masses of fibrous roots and clump-like growth, or make offsets, or sucker growth. It must be remembered that where varieties are grafted on to common stock, as in lilacs, the sucker growths will be those of the common stock, Syringa vulgaris, and not the desirable variety.

Among the shrubs which may be propagated by division or by offsets are amelanchiers, Fuchsia magellanica, Hypericum calcyinum, Kerria japonica, lavandulas, mahonias, rubus, certain spiraeas and syringas, remembering the proviso mentioned above.

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11. October 2010 by Dave Pinkney
Categories: Herbaceous Plants, Plants & Trees, Propagating, Pruning | Tags: , | Comments Off on Propagating Plants – Methods of Plant Propagation

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