Vegetative Propagation: Division, Cuttings, Grafting and Budding
The simple division of clumps or clusters is a common practice and one of the easiest ways of building up a stock of plants. All that is required is to lift a crown, usually consisting of a mat of roots and stems, split off sections and replant these divisions which are usually known as offsets. It is wise to select the younger plant material from the edge of the clumps and discard the harder older growth of the centre. Rhubarb and herbs such as pot marjoram, thyme andcan be increased by this method.
Bulb division is a natural and fairly obvious way with which to propagate stocks ofand potato . Given good cultivation, one shallot division planted in spring will yield eight or nine fine bulbs by late summer.
Bulbils or small bulbs are sometimes produced on the flowering stalk where one would normally expect to find flowers or seeds—a peculiarity quite often found with various members of the onion family.
The production of these bulbils is quite common with the tree onion, but less so with onions, while leek bulbils are much sought after by keen exhibitors. These minute bulbs are carefully removed from the seed head, potted up and overwintered under glass.
Bulb segments or scales are used to propagate, planted in autumn or spring. The bulb segments of garlic are known as ‘cloves’.
Tubers are probably one of the best-known plant parts used for vegetative propagation by division, the potato being the most important crop increased in this way. Jerusalem and Chinese artichokes can also be propagated by planting their tubers.
An examination of a potato tuber will reveal a number of minute, dormant buds or eyes, each of which is capable of producing a new potato plant and thus eventually more tubers. When there is a scarcity of the so-called ‘seed’or ‘sets’ (dormant tubers from which potatoes are grown), gardeners and farmers cut potato tubers into two or more pieces, each with at least one eye or bud, and plant these divisions.
Induced increase of stock
The following methods of propagating plants are those in which nature is assisted, and some form of cutting is involved in the process.
Where there is an open wound, as with the taking ofor the preparing of grafts, you should pay careful attention to plant hygiene and encourage quick growth of the new plant. Plant diseases are abundant and prevention is better than cure. A clean cut with a really sharp knife enables the plant to form a callus— a protective layer over the wound— much more rapidly than does a rough jagged wound. You can help certain cuttings, especially soft and semi- , to form roots more speedily and protect them from fungus diseases by dipping them in a preparation of rooting hormone and fungicide.
Stem cuttings are soft or ‘tip’ cuttings, half-ripe or semi-hardwood cuttings, and hardwood cuttings.
Soft stem cuttings
A few vegetable crops can be raised from soft stem cuttings, but gardeners rarely use this method in the kitchen garden except in the propagation of. Shoots about 5-7.5 cm (2-3”) long, cut just below a leaf joint, can be rooted in pots of cutting , which must be kept moist. Soft stem cuttings are usually taken in late spring or early summer, sometimes also in early autumn. They are always the tips of new season’s shoots and are entirely green and soft. They are more liable to rot from diseases than the other two types, but are usually quicker and easier to root.
This type of cutting consists of shoots 10-15 cm (4-6”) long, which ideally should be healthy, vigorous and not in flower or carrying flower buds. The bark will be brown and hard at the end of the shoot where it originates from the parent stem, but about halfway along its length, the shoot will start to become soft and green. These growths can be prepared with or without a ‘heel’.
Node cuttings, without a ‘heel’, are cut cleanly just below a leaf joint. Heel cuttings are sideshoots which have been pulled off with a portion of stem attached, and are usually short—no more than 10 cm (4”), sometimes less. Some gardeners find thatroot better than node slips.
Sage and rosemary can be propagated easily from this type of cutting, taken in the summer and rooted in prepared compost in shaded frames. Perennial kales can also be propagated by this method.
These are taken in autumn, and consist of new growth about 20-30 cm (8-12”) long and trimmed off cleanly below a leaf joint or scar. The shoot should be fully ripened; that is, the bark should be brown and hard but smooth almost all the way along the shoot. Only the end 2-3 cm (1-1/2”) should still be soft and green. These cuttings are inserted about 15 cm (6”) deep in ‘V’ shaped trenches in a sheltered site outdoors.
Currants and gooseberries are raised from this type of cutting. As both red and white currants and gooseberries are raised on a ‘leg’, the buds are removed from the lower two-thirds of each shoot.
Bud or eye cuttings
Vines are increased from 5 cm (2”) pencil-thin cuttings taken in winter and having one plump bud, or ‘eye’. These are placed in suitable moist cutting compost and raised in warmth, supplied to the compost as well as the air, if possible.
Fleshy-rooted plants such asand horseradish can be propagated from roughly 15 cm (6”) long pencil-thick sections of root. These are cut straight across at the top, but have a slanting cut at the lower end to distinguish top from bottom; they are then put straight into the ground where they are to be grown. In the case of seakale, they are known as ‘thongs’.
Grafting and budding
Choice varieties of apples, pears and other tree fruits are grafted or budded on to specially selected rootstocks. Plant breeders have also produced disease-resistant varieties of tomatoes by. It is now possible to grow fruit trees almost by prescription, and with some measure of disease resistance, thanks to the development of modern rootstocks.
The gardener is most likely to want to attempt grafting in order to convert an existing variety of apples which is cropping badly, or is not suitable, to another. This can be later or earlier cropping, or even culinary instead of dessert, given a suitable rootstock.
Such a conversion is called framework grafting and, if you like, two or more varieties suitable for pollinating each other can be grafted onto one tree, thus producing what is known as a ‘family’ tree.
The existing tree is cut back during winter so as to leave only the largest branches, about eight to twelve of them, with side branches cut back to stubs, perhaps 15 cm (6”) long. These should be regularly spaced, and should have a herringbone formation, as viewed from the sides of the main branches, rather than from the top of them or below. The scions are then stub or side-grafted onto them in early spring, and should have at least seven dormant buds on each.
The end of the scion is cut to a wedge, with a longer cut on the lower side, and another cut made in the upper side of the stub, half way through it. The scion should more or less correspond in thickness to the stub, so that as much of the cambium as possible is in contact; otherwise put the scion to one side or other. Insert the scion to match the cut surfaces as closely as possible, secure them with raffia and cover with grafting wax. Cut the stub back to just above the graft, and cut the end of the main branch similarly when the graft has taken.
Side grafting can also be carried out; this involves grafting the scion straight into the side of a main branch, preferably one of the smaller ones. The scion is cut to form an unequally sided and longish wedge, and the branch to be grafted has a slanting cut made in it at the side, to a depth of not more than a quarter of the diameter of the branch. While the cut is held open by slightly bending the branch, the scion is inserted so that it emerges at as natural an angle as possible. Stub and side-grafting can both be used on the same tree.
Whip-and-tongue grafting Whip-and-tongue grafting is used for nursery work, to graft a variety onto the chosen rootstock and so produce a maiden tree. This is done in early spring. It is very important that the scion and stock should be of the same diameter for greatest success. Slanting cuts are made on the lower end of the scion and a ‘tongue’ nicked out of it; the stock has its leading shoot cut about 10 cm (4”) above the ground, also on a long slant but in the reverse direction and with a tongue in approximately the same position, so that the two inter-lock when the scion is fitted to the stock.
Again, as much cambium as possible should touch; the scion should have about four buds on it, and be cut just above the top one. In early summer the lowest shoots on the scion are cut back to about five leaves, the leader is allowed to grow, and any shoots on the stock are removed completely as soon as they appear. In autumn all shoots but the leading shoots are completely removed.
Budding is a form of grafting, in which a scion, consisting of a single bud, with wood backing it and bark surrounding it, is used—mainly for peaches, plums, cherries, quinces and apples.
Chip budding has recently been found to produce the best results. The bud is removed from the scion by cutting the stem about 1.3-2.5 cm (1/2-1”) above the bud and extending this behind the bud to about 1.3 cm (1”) below it. A second cut is made immediately below the bud to meet the lower part of the first cut. The stock is then cut to fit the bud, which is inserted so that the cambium of both surfaces fits at the top and the sides, as far as possible, being then tied and sealed with grafting wax. Chip budding is used mainly to produce new trees.