Grafting of Plants
The need for grafting arises from the fact that very many plants will not propagate reliably from cuttings.
Nurserymen also find that they can raise more plants more quickly by using standard rootstocks.
Grafting of plants appeals to many gardeners and it can be a rewarding and exciting way of raising young trees and bushes and, especially where fruit trees and their ornamental relatives are concerned, converting old but healthy trees to better varieties.
The aim of grafting is to unite two or more stem parts of a selected variety—the scions, and a suitable rooted shoot—the rootstock. In some respects it is a matter of carpentry, clean sharp cuts and good joints. The rootstock which forms the root system and part of the main stem is a selected seedling. The Malling and Malling-Merton rootstocks for fruit trees are well-known, highly developed forms. These rootstocks are propagated vegetatively and are one year old in the nursery before being grafted. The scions are young and usually one year-old shoots or buds from selected varieties, which it is intended to grow.
The principles behind grafting and budding are (a) the rootstock and scion must be closely related to each other, they are thus compatible, (b) there must be continuous close contact between exposed living cells, the cambium layer between the bark and the wood.
Grafting can be done at any time of the year but for hardy fruits the work is carried out in the spring and early summer, March to May. It is at this time that cell sap in the rootstock is flowing steadily and union between cut surfaces takes place readily. This is important for a firm permanent union. A simple test of the condition of tissue is the ease with which the thin rind or bark peels off.
The all-important cambium cells are underneath the rind and are seen as a thin white or cream line, quite visible under a low-powered lens. The skill of the operation is to bring as much of the cambium as possible on the scion (or bud) into contact with that of the rootstock.
Grafting young trees There are several ways of grafting young trees but the most common is the whip and tongue method, though there are a number of modifications of this. Scion wood is taken from selected plants and in the main is one year old. For outdoor grafting take enough shoots from dormant plants, tie and label them securely and store them in moist peat in a cool shady spot. Each shoot generally provides two or three scions, each with about four buds. To carry out the operation in spring, have a sharp pruning knife, a small, fine-grained carborundum stone and a pair of sharp secateurs. To hold the graft area securely use wetted raffia or plastic strips and seal the wounds with a cold bitumen wax.
The stocks to be grafted should, in general, be little more than pencil thickness and have been established in the ground at least one season (stem building trees to make family trees may be 3-4 seasons old). The rootstock to be grafted is cut off at a reasonable height above ground level, certainly no lower than 16cm (6in). With the pruning knife make a clean sloping cut 4cm (1 1/2 in) long on one side of the stock. About 1 cm (1/2 in) down from the top of this sloping cut, a cut is made to form a tongue 0.5cm (1/4 in) long. From the selected scion wood cut off a four-bud scion.
On one side of this make an even sloping cut 4cm (1 1/2 in) long to match that on the rootstock. About 1cm (1/2 in) from the top of this sloping cut make a 0.5cm (1/4 in) tongue to match the one on the rootstock.
The scion is then edged on to the stock so that the edges of the cuts correspond and the tongues interlock into each other. To aid union, the scion and the rootstock are bound together with wetted raffia or plastic and the whole wound area painted with a cold bitumen wax or enclosed with polythene.
In this way the parts are held securely and rain is prevented from getting into the graft.
With some varieties of pears, direct union with quince rootstock is uncertain and double working with mutually compatible intermediate varieties is carried out. The mechanics of the business are similar to the foregoing.
The two pear scions are grafted together first, with the intermediate in the bottom position. Immediately this is done the final link up with the quince rootstock is done. It is also possible to bud or Williams' Bon Chretien is double worked and for this variety Beurre Hardy is a good intermediate.
There are a number of trees and shrub plants which can be grafted easily indoors in a warm greenhouse or frame and for these the simple whip graft techniques are sufficient.
The rootstock and scion are tied together and put into moist peat in a heated frame. In this moist warm atmosphere the parts heal together quickly and in a week or two, depending on genus and species, are ready to be potted up and grown on in the cooler atmosphere of the greenhouse bench.
After care When buds begin to grow from newly grafted plants in early summer there should be no rush to take off surplus buds.
So often buds show activity and then dry up, a sure sign that union has failed. If the buds really get away and form shoots, union is satisfactory. At this stage remove rootstock shoots completely as they appear, and also any on intermediate scions. If it is the intention to produce single-stem maiden plants the best shoot is allowed to grow and the remainder cut out completely. To avoid accidents tie this shoot to a nearby cane as it grows. When, however, as with many ornamental plants—syringas (lilac), cytisus (broom) a leg or stem is not needed, the rootstock buds only are removed and the graft shoots grow unhindered.
With indoor grafting, wait until the scion has made 3-5cm (1-2in) of steady growth before potting the plants for growing on.
At all times in the nursery or greenhouse keep a lookout for insect pests and diseases which can cause loss.
With fruit, the family tree has become popular. For this a rootstock is pruned at a selected height to form 4-5 branches. On to each of these branches a different scion variety is grafted. In this way, in a small garden, several varieties of different fruits can be grown as trees. The method is used especially with apples, pears and sometimes plums. The varieties are chosen to give a succession of ripening and help each other with pollination.
A similar method called stem building is used with plums and sweet cherries. A rootstock or main stem resistant to silver leaf disease or bacterial canker forms the early branches and subsequently the crotch where these troubles often start.
Root grafting This method of grafting clematis hybrids is an indoor operation.
Seedlings of Clematis vitalba (old man's beard) are used and scions are cut from clematis plants put in a warm greenhouse in January. Grafting is done from February to March. The seedling stocks are cut back to the root portion and the scion prepared by cutting off a portion of stem with 2.5cm (1 in) of wood above and below the leaves. Two wedge cuts 2-2.5cm (3/4 1in) long are made in the stock and the scion stem is split with a sharp knife.
Each portion is placed saddle-wise over the prepared stock, secured with raffia and planted in a propagating case to grow on.
Varieties of gypsophila can be raised in a similar fashion using seedling roots, though simple matching cuts on scion and stock are sufficient.
Budding This form of grafting can be used for raising a range of fruit and ornamental plants. The bud is the scion from a selected variety. All varieties of tree fruits and other ornamental relatives can be raised by budding. The operation is done in summer when the cell sap is flowing easily.
Rootstocks to be budded should have been planted one year.
But sticks consisting of one-year-old, half-ripened shoots with several buds are taken from chosen plants in July. About 23cm (9in) above ground level make a vertical cut 4cm (1.5 in) long in the bark of the rootstock. At the top of this make another shorter cut at right angles, thus forming a 'T'. With the end of the knife partly raise the edges of the cuts. To prepare the buds hold a bud stick firmly and with the knife make a cut 1 cm (tin) above a bud. Carry the cut just underneath the bud and surface about 2.5cm (tin) below. The best buds are found in the middle of the shoots. With the knife edge ease the 'tail' of the bud under the long cut on the stock so that the bud will fit snugly on the exposed cambium cells. At the top of the 'T' cut off any spare end and bind the parts with plastic tape or raffia and cover the wound area with petroleum jelly. The bud, if well fitted, will remain dormant until the following spring and then begin to grow and make a shoot. As soon as this is growing well, cut off the rootstock just above the budding area. Tie the young shoot to a cane as it grows.
Bridge grafting This is used to repair damage done to the main stem or branches, eg when they have been stripped of bark by animals. Scions long enough to stretch across the damaged area are prepared with a wedge cut at each end and pressed into bark cuts made into healthy tissue. This method is also used as support bracing between main branches when these are likely to break away.
Grafting established trees In many gardens there are trees which are old but quite healthy or undesirable varieties. These can be converted to new varieties by grafting. There are two
main ways of doing this—top working or frame working in spring.
The former consists of shortening all the main branches to within 0.6-1m (2-3ft) of the crotch or crown. To avoid having large wounds (those with a greater diameter than 10cm [4in] heal slowly) it is advisable t6 cut the main branches higher so that this diameter is not exceeded. A few small branches, known as sap drawers, can be left in position below where the cuts are made.
The branches can be cut back any time during the winter months. The sap drawers will help to feed the roots and keep the branches healthy, but can be removed as soon as the grafts or scions have taken. It is usual to put more than one scion on 7-10cm (3-4in) cuts and one scion only on small cuts.
Cleft or oblique cleft This method is also known as crown grafting. Cuts are made across the flat surface with a sharp chopper or special tool. Scions are prepared and pushed into the cleft which is kept open, and when they are in position the scions are held firmly by the wood. With oblique cleft grafting the cut is made a short way only into the limb. Remember to cover all cut surfaces with bitumen to shed off surplus water and keep out disease spores.
Rind, bark or veneer grafting This is another method of doing the same job. Here a vertical slit is made in the limb and a pointed scion pushed into the wood and the bark. This scion is held in position by tying the graft round with string, raffia or adhesive tape which must be cut as soon as the scion begins to grow two or three months after the job has been done.
It will be necessary to give some support to the young branches and this can be done by tying them loosely to canes bound tightly to the branches of the tree. The trees which have been top worked may take 5-6 years to crop once again, and a new framework or branch 8 system has to be developed by pruning.
Frameworking This is a means of bringing the trees into cropping earlier, but many more scions are needed than for top working. Again, in the winter season, dead, diseased or badly placed branches are removed completely, but much of the remaining branch system left untouched, except for the removal of overcrowding shoots.
Stub grafting is the most common method of putting shoots into a framework. To do this successfully leave as many young shoots as possible in the tree, those from 1-2.5cm (1/2 1 in) in diameter. Stubs are inserted into the branches by making a cut about 1cm (tin) along the side shoots from the main branch, and bending this back so that the prepared stub can be pushed into position. The main shoot is released and grips the stub firmly.
The remainder of the lateral which is to be replaced is cut about 1cm (tin) from the stub position. Again, cover all wounds with sealing material. Avoid placing stubs or scions on the top or underside of a branch, but put them mainly on the side of the branch in herring-bone fashion and approximately 30-37cm (12-15in) apart. Stub grafting can be started as early as February and continued into May. On branches thicker than 2.5cm (1 in) cuts are made into the bark, the branch bent back to open the cut and the stub pushed into position. This is called side grafting.
Side grafting Scions for top working should have 3-4 wood buds, while those for frame working can be longer, about 7-8 buds and never less than six.
Frameworked trees will come into cropping within 2-3 years after treatment.
There are many other forms of grafting, including approach, bottle, inarch, inlay, kerf, peg, ring, saddle and strap. Some are for special purposes and the others are of general use when circumstances allow.
It is not always understood that ornamental trees can be top worked and frameworked in the same way as fruiting plants.
Pruning of grafted trees The first thing to remember about grafted trees is that the original branches will make every endeavour to produce new shoots and these should be removed as soon as they appear and certainly not be left on longer than 7-10cm (3-4in). This will mean going over the trees two or three times during the summer and for several years after the job has been done, otherwise there may be a mix up in the tree and the undesirable variety used as the stock could, in time, take over from the new one. It is sometimes possible to detect the branches of the original tree during the winter months, when they can be pruned out completely. Water shoots, ie strong growths growing from the crotch of the tree, will also grow quite strongly and these should be removed at the same time.
Top worked trees can often be distinguished among others growing in a natural fashion by the fact that most of the branches grow very upright. This is due to the fact that sap in the young branches produces strong growth and it may be 6-8 years before these trees really begin to produce crops of fruit. To assist the tree, however, pruning of these strong shoots should be carried out each winter after grafting. Do not prune the leading shoot too hard; simply remove about 20-30cm (8-12in) of the end. This will encourage side shoots to grow and it is on these that fruit buds and fruit will appear. Strong growing, hard pruned shoots take a long time to form fruit buds. If you have put in more grafts than necessary, cut out the surplus, again in the first winter after grafting, and leave in those which are strongest and best placed. Many gardeners find it advisable to keep the cane support for each branch for a year or two so that this does not blow out after a gale. After a year or two grafted branches become as firm as any others.
When dealing with frameworked trees the general treatment is the same but the grafts do not make such vigorous growths and are, in fact, simply new laterals taking the place of the old.
Because they are less vigorous they will form fruit buds and fruits probably in the first year and certainly in the second. Pruning of these can be done in the ordinary way eg for apples and pears they can be spur pruned to 7-10cm (3-4in) or left full length as is done with plums and sweet cherries.
Remember that grafting is a skilled operation, use a sharp knife, make clean cuts, bind firmly where necessary and cover all wounds so that disease germs do not get in.