Propagating Shrubs and Trees – Layering/Air Layering
Propagating Shrubs and Trees by Layering
Layering is a good method of and trees that are particularly difficult to raise from cuttings. There are many kinds which lend themselves to this method of increase, including azaleas, rhododendrons, all the viburnums, magnolias, kalmias, camellias, daphnes, lilacs, cotoneasters, clematis and wisteria. Layering actually mimics the process by which some species propagate themselves naturally anyway.
Branches on many plants come into contact with the ground as they grow or are weighed down by their foliage and from this point, buds can shoot roots into the ground and this new root system will eventually become established enough to support the branch as a plant in its own right.
The Method of Layering
Layering merely involves the rooting of shoots or branches while they are still attached to the parent plant. The best time, I find, is in the spring but it can also be done throughout the summer. Choose a branch or shoot that is near to the, or one that can be brought down comfortably to soil level; and always use a shoot of the previous year’s growth, not an old shoot.
Before I peg down the layer I prepare the soil thoroughly by forking it over and incorporating liberal quantities of peat and sand. To prepare the shoot, make a 2 inch long slit with a sharp knife, half way through it, lengthways, and preferably through a joint. This cut should be made 9 to 12 inches from the tip of the shoot.
Then make a depression in the prepared soil about 3 to 4 inches deep. The part of the stem which has been cut is pegged down into this hollow, ensuring that the cut remains open. Use either a wire or wooden peg. I always tie the shoot to a i cane so that it is held in an upright position. Then the part of the shoot which is pegged down is covered with soil which must be made really firm. After layering, just keep the soil moist until the shoot has rooted. Placing a large, flat stone over the layered part of the branch will help to keep it moist and assist in good root formation.
The Rooted Layers
Some layers will root during the same summer, in which case they can be severed from the parent plant in the autumn and planted in a nursery bed. Others, such as rhododendrons, azaleas and kalmias, usually take two seasons to form their roots. No layers should be severed until a good root system has been formed.
Air Layering Shrubs and Trees
Air layering is also an easy way of increasing or propagating shrubs and trees that are particularly difficult to raise from cuttings; for example, azaleas, rhododendrons, acers, and magnolias. It is basically the same as ordinary layering except that the shoot is not rooted in the soil but in its normal position on the plant, the prepared area being enclosed in wet sphagnum moss which is held in place with a polythene sleeve. I do my air layering in May or early June.
The Method of Air Layering
Again, it is a matter of selecting a shoot of the previous year’s growth and making an incision as I have just described for normal layering. The cut should be kept open with a small piece of wood and then dusted with a hormone rooting powder. There is a rooting powder on the market especially for air layering. The cut is wrapped in a large handful of wet sphagnum moss – some is pushed inside the cut and then covered with a polythene sleeve. This must fit fairly tightly and each end is sealed to retain moisture.
You will be able to tell quite easily when the air layer has rooted as the white roots will begin to emerge through the moss. At this stage the layer may be severed from the parent plant and potted. Water it in well and place it in a propagating case or a polythene tent until it becomes established in the pot.
Read more about air layering roses to see exactly how this propagation method works.
A Grafting is a more specialised form of propagation and is a quick method of raising plants. It is particularly suitable for hybrid kinds which you want to be true to type.
Grafting involves uniting living parts of plants so that they form a permanent union. One plant supplies the root system only and is called the ‘stock’. A small part of the plant of the variety required is joined to the stock and is known as the ‘scion’. This eventually produces the shoots and branches.
It is essential that the stock and scion should be compatible ie. that they will unite or grow together. In most cases they are of the same genus. Sometimes plants of different genera can be grafted – for example, amelanchier on to Sorbus aucuparia.
Selection of Stocks
Varieties ofcan be grafted on to the common holly; Crab Apples on to the common Crab or apple stocks; ornamental peaches, plums and almonds on to Common Mussel plum stock; ornamental cherries on to Prunus avium, the Gean or wild cherry; rhododendrons on to R. ponticum; amelanchier and varieties of Mountain Ash on to Sorbus aucuparia; crataegus varieties on to the common Quickthorn and laburnums on to L. vulgare. You will notice that most plant varieties are grafted on to their common counterpart.
Preparation of Stocks
The stocks are bought from nurseries and planted in rich, well prepared soil during October or November. They are then left to grow until the following March when grafting can take place. During this time it pays to rub off all buds on the stems 9 to 12 inches from the ground.
Selecting the Scions
I use one year old shoots for grafting as these are not too thick. They can be cut from the parent plant in February, tied in bundles and heeled in under a north wall until they are required in March. Just before use they must be washed free of soil.
Whip and Tongue Grafting
This is the most popular method and is used for propagating shrubs and trees of many varieties. For this, and any other type of grafting, always use a really sharp knife.
First, the stock is cut down to within 3 or 4 inches of the ground, then a slanting upward cut, 1-1/2 inches long, is made at the top of the stock. This should remove about half the thickness of the stock.
Then a small downward cut is made in the cut surface near the top, thereby forming a ‘tongue’. To prepare the scion, the selected shoots are cut so that each piece contains three or four buds. Do not use the soft tips of the shoots. The base of the scion is prepared by making a slanting downward cut similar to the one on the stock, but opposite a bud. Then a tongue is cut so that it corresponds with the one on the stock.
The tongue of the scion is fitted into the one on the stock. If the cut surfaces are perfectly smooth they will fit closely together. The graft is then bound very tightly with raffia which in turn is covered with grafting wax to render it airtight and watertight. If the widths of stock and scion differ, then it is essential that one side of each should meet perfectly. This is to allow the cambium layers – seen immediately under the bark of stock and scion to unite. Unless the cambium layers meet somewhere a union will not occur.
Once the scion is growing vigorously the raffia may be cut away, and shoots or buds which appear on the stock should be rubbed out regularly.