There are several plant propagation techniques and this article covers the plant propagation technique of.
Layering is really suitable only for woody-stemmed plants — shrubs and trees, including some house plants. This method often succeeds where fail. Some , notably carnations and pinks, will also respond to layering.
Many of the pendulous or lax-stemmed shrubs and trees, such as suspensa and Salix x chrysocoma, layer themselves naturally when their stems touch the ground. The constant rubbing of the branch against the ground causes an injury to the bark, and roots develop from the callus formed over the wound to anchor the branch.
The best branches for layering are non-flowering ones that have grown in the current year — that is, the freshest, smoothest shoots. Deciduous plants are best layered in autumn or winter; evergreens in autumn or spring.
First, fork over the surface of the soil around the plant. Choose any flexible branch and bend it down until it reaches the ground 23-30cm (9-12in) from the tip, held at an upright angle. Strip the leaves off the branch where it touches the soil.
Wound the underside of the branch to restrict the flow of sap by cutting a shallow tongue with a knife, cutting towards the growing tip. Alternatively, twist the branch to injure the tissue. Dig a hole 7.5-10cm (3-4in) deep beneath the wound and part-fill it with a proprietary seed or potting . A light dusting of a proprietary hormone rooting powder over the wound may encourage quicker rooting, but is not essential.
Push the wounded part of the branch into the hole, forming a right-angle at the wound. Peg the branch to the ground with a bent piece of galvanized wire, 15-20cm (6-8in) long, and stake the upright tip. Fill the hole with more compost. Repeat with other branches. Water the area thoroughly,. and ensure that it never dries out.
Check the new roots by carefully scraping away the soil. Most ornamental shrubs take six to twelve months to root sufficiently, though magnolias and require up to two years before they can be severed from the parent plants. If roots are well established, sever the new plant from the parent, lift with a good ball of soil and plant elsewhere in the garden.
If the roots are not well grown, but the layer is healthy, replace the soil and leave it for a few more months before re-examining the root formation.
Certain plants can be propagated simply by burying the tips of their shoots in the soil — brambles such as blackberries and loganberries are particularly successful.
Towards the end of mid summer, bend down a new season’s shoot and, where it touches the ground, dig a 15cm (6in) hole with a hand trowel. Plant the entire tip of the shoot in the hole and firm it in. Peg down the shoot if it is particularly springy.
By mid autumn the tips will have rooted. Sever each new plant from its parent by cutting just above a bud. Do not move the plant yet. In late autumn transfer each new cane to its permanent bed. It will bear fruit in either its second or third year.
A handy plant propagation technique of propagating woody plants with long pliable stems — especially , such as honeysuckle, clematis and jasmine — is called serpentine layering. It should be done at the same time as ordinary layering. Use long, trailing shoots that have grown during the current year.
Bend a shoot to the ground carefully and, where it reaches the soil, dig a 5cm (2in) deep hole beneath it. Wound the shoot underneath as for ordinary layering. Peg the wounded part of the shoot into the hole with a piece of bent wire or a small forked twig. Fill in the hole with a proprietary seed or potting compost.
Cover with garden soil and firm in with your fingers. Leave the next two pairs of leaves above ground and repeat the operation. Continue this way along the entire length of the shoot.
One year later, the serpentine layer should have rooted. Scrape the soil away from each buried section of the layer and, if it is well rooted, sever it from the preceding section with secateurs. (If it is not well rooted, bury the whole layer again and check it a few months later.) Each rooted section is now ready to be severed and planted out in the normal way.
Transplanting is made easier if, instead of pegging the shoots into holes in the ground, they are pegged into pots of compost sunk into the ground. When the layer has rooted it can then be severed and moved without disturbing the new roots.
Growing from Runners
A runner is a type of aerial or underground stem which, when it comes into contact with moist soil, roots along the stem and forms new plants — a form of natural layering.
The runners formed by healthy strawberry plants, and other ornamental members of the genus Fragaria, provide an easy means of propagation. In early summer, anchor the plantlets with pegs if the plants are grown in matted rows. Let them root into the soil, removing the remainder of the runners beyond the first plant.
Alternatively, select the strongest plantlets and peg them down into pots, sunk to their rim in the soil, and containing John Innes potting compost No.1. Water the pots frequently to aid root formation and remove all other runners as they form.
The plantlets should be separated from the parent in mid to late summer and planted out from their pots. If, for some reason, planting is delayed until the autumn, the young strawberry plants should not be allowed to fruit the first season. Pinch out the flowers as they appear.
Some house plants, notably mother-of-thousands ( stolonifera) and spider plant (Chlorophytum comosum), also produce small plants either on the flowering spikes or on thin runners from the parent plant.
With mother-of-thousands, detach the thread-like runners, each of which bears a plantlet, from the parent plant. Nip off the runner from the plantlet. Fill a small pot with moist John Innes No.1 potting compost.
Make a shallow depression in the surface and set the plantlet in it. Firm the compost round the base of the plant. Do not water, but place a polythene bag over the pot and secure it with a rubber band. Keep the pot out of direct sunlight and at a temperature of 18-21° C (64-70°F). Condensation should ensure that the compost does not dry out; otherwise water gently.
After about ten days, the plant-let should have rooted. Remove the bag and set the pot in a lighter and cooler place.
Spider plants often bear a number of plantlets on tough stalks. These can be layered into individual small pots of John Innes No.2 potting compost and secured with wire clips. After about three weeks, the plantlets should have rooted enough to be severed.
When branches are too stiff or too high to be layered at soil level, they may be ‘layered’ in the air. This can be done between late spring and mid summer Air layering is particularly recommended for Ficus species, such as the common rubber plant, and for magnolias. This method of propagation is sometimes known as Chinese layering.
After some years, house plants such as dizzygothecas and rubber plants may grow too tall, and will often lose their lower leaves. Rather than throw the plant out, propagate it by air layering in spring to produce a new, shorter stemmed plant.
Select a stretch of the branch of the current year’s growth and strip off the leaves in the middle. Then cut off a shallow slice of wood and put rooting powder on the cut.
Wrap a sheet of polythene around the area of the cut and tie the bottom of it with raffia or string. Fill the open-topped tube with a mixture of equal parts moist peat, coarse sand and sphagnum moss. Fasten the top with more string or raffia.
The conditions needed for rooting of the air layer are constant moisture, exclusion of sunlight and restriction of the stem. Therefore, it is necessary to use black polythene and well-moistened rooting mixture. Once the polythene is sealed, no further watering will be needed.
In three to six months, when rooted — check by unfastening the top of the polythene — remove the polythene and cut off below the roots. Pot up the new plant into a 11-15cm (4-½ – 6in) pot containing a proprietary potting compost.
Place the potted plant in a closed frame for two weeks and keep it moist, then harden it off. This entails opening the frame during the day, gradually admitting more air until the frame is left open entirely. Plant out the following spring.