Time for deciduous Grafting:
Grafting is probably a rather mystical practise to many, but once a few basic principles are understood, then grafting is well within the realms of possibility for the keen gardener.
There are several reasons why grafting is practiced, the main one being that it is the only way to propagate a wide range of desirable plants. Grafting is also done to combine desirable characteristics of two plants into one as in the case of dwarfing rootstocks producing manageable plants for the home garden. Some fruit trees such as pears and plums require pollinators so when the right combination is grafted onto the one rootstock then one tree can be planted where normally two would be required. This practice can be used to build up a range of varieties on a tree to extend the fruiting season. It was said that Luther Burbank, a Californian plant breeder, had 144 varieties grafted on the one apple tree.
For grafting to be successful there are three basic components to keep in mind:
The rootstock
This is the root system which is to support the grafted plant for the rest of its life. Different rootstocks are used for various reasons such as dwarfing, disease resistance and soil conditions. The rootstock must be closely related to the scion variety. When topworking a tree it could be refered to as the recipient branch.
The scion
This is the selected part which produces the desired fruit or flowers on the mature plant. Scion varieties are refered to as clones and are usually named for easy reference such as apple 'Gala' or plum 'Burbank'.
The cambium layer:
This is a thin layer of cells between the bark and the wood of plant stems which divide to increase the strength and thickness of the stems. It is usually greenish in colour and when a plant is actively growing the bark can be easily peeled off the stem to expose the cambium layer, since this is where the cells are dividing and have no strong bonding tissues between the cells.
When grafting it is important to get the cambium layers of both the rootstock and the scion variety as close together as possible so that when the cells start dividing the union heals quickly. To achieve this it is important to make all cuts as clean and straight as possible, and to tie the graft securely so that there is no movement in the graft union.
The method:
A good sharp knife (razor sharp, with a thin blade) is important for making the cuts and the cutting should be done with a slicing motion rather than trying to drag the knife through the wood. This is the trickiest part of the operation where there has to be forward motion of the knife in the cut as well as a constant awareness of where the knife is going to go if it slips. There are probably as many techniques for this as there are grafters, and as long as safety is considered and a clean straight cut is achieved, satisfactory results should follow.
Most good gardening books will contain at least a small section on grafting and grafting methods, but my prefered method for deciduous grafting is the 'whip and tongue' system. This method is best done on branches where the scion is as close to the same diameter as the recipient branch as possible. The scion should be about ten centimetres long with at least three good buds on it, and if the top has been cut off it should be dressed with pruning paste once the graft is tied and completed.
The whip and tongue graft is very useful for adding new varieties or pollinators to established trees, as well as grafting one or two year old seedlings with named fruiting varieties. The only species that have not responded readily to this method are grapes and walnuts. Both these plants tend to bleed readily on warm days at any time through the winter.
The first cut is at about thirty-five to forty degrees through both the scion and the stock branches. If you keep away from the buds when cutting then the cuts will be safer to do and easier to keep straight.
The cutting of the tongue is the most difficult part of the method, and is done by holding each cut portion with the point upwards and starting the cut one third down from the top and slicing in at a slight angle until this cut is about one third the length of the original cut. If there are any splits as in the illustration, care must be taken when putting the graft together so that each tongue fits in the correct position. Care should be taken to avoid loose bits of pith in the cuts too.
When this proceedure is followed on the other portion to be joined then both pieces will slide together with each tongue sliding under the other, to leave a cut that is more or less shaped like a "z".
The graft is ready to tie and this can be done with insulation tape which has been sliced in half lengthwise on the roll, since the narrower tape is easier to keep smooth as it goes around the stem. It is important not to leave any gaps when tying.
If black tape is used the heat it attracts will speed up the healing process, since this wrapped part of the stem can get up to five degrees warmer on a sunny day. This tape stays on till about mid December and most types of tape have enough elasticity to stretch a little as the stem thickens.
This method is based on about twenty years experience and can be used anytime from when trees go deciduous in the autumn until growth commences in spring, as long as the scion is dormant. If the scions are shrink wrapped in plastic and stored in the fridge they can be grafted any time up until early December, as long as they don't dehydrate during storage.
Another method which is still on the drawing board (and I welcome any feedback on this one) is one which avoids the tricky aspect of cutting the tongue, which is THE MOST DANGEROUS PART OF THE OPERATION. The theory is to pin the scion and stock together rather than rely on a tongue to hold them in place. It should work as long as the stem diameters are the same and the cuts are close to the same shape and size. It is awkward to do, but it may be easier to tie it then pin through the graft at a slight angle. Care should be taken to make sure the pin goes through at right angles to the cuts. Make sure the pin is very thin. The one in the illustration is a "Panel Pin". A little nail polish or vaseline around the pin on both sides will make sure all moisture is kept out.
When grafting plants in containers it is helpful to dry the root system out quite well, but not totally, and this minimises any bleeding, which is unwanted sap flow. Unwanted bleeding allows infections to establish in the graft union, and these usually cause the graft to fail.
This is a mirror page to an article on the New Zealand Gardens Online pages.