From the April 1990 Fruit Gardener Magazine of the CRFG

ELEMENTS OF GRAFTING

From the Scion Exchange Newsletter of CRFG Northern California Chapters

Grafting is the botanical equivalent of a human organ transplant. The donor parts are taken from a stick called a scion. Incisions in the form of whittling are made in a way to properly join the parts. The parts are bound together after being carefully aligned. The wounds are then covered or sealed. Fortunately, all of the required skill and knowledge can be easily acquired such that the first-time grafter can be fairly successful.

It is important to note that, just as in a human transplant, rejection of the donor parts will occur if the parts are not well matched (by fruit type). To assure proper matching, all scions should be carefully labeled.

The matching is very simple. Fruits of the same type are usually compatible. The accompanying chart shows the compatibility of common deciduous fruit trees.

A European plum scion grafted onto a Japanese plum or a vigorous (standard) and slow (genetic dwarf) combination of apple (or possibly other fruits) may produce graft unions that are weak or short-lived.

There are many other things to consider when selecting a scion. The most important of these are the amount of winter chilling required for proper bud development and the amount of heat required for good fruit ripening. These vary for different varieties of fruit within the same fruit family. Climate zones should be checked. The following things should also be considered:

flavor, how long fruit hangs or holds on the tree when ripe, how well the fruit stores, stone type (cling, semi-cling, free), disease resistance, time of ripening, and pollination requirements. The color and size of the fruit are often overrated qualities and should be of a lesser concern.

The ideal scion may be about as thick as a pencil or slightly thicker. Scions from two-year old wood with no flower buds work best. Flower buds usually appear on one or both sides of a leaf bud. If you find two or more buds clumped together there are probably one leaf bud and one or more flower buds there. Newly grafted branches cannot support the development of fruit so the flower buds are removed from such scions. The leaf bud, which should be a lone bud or the center bud where there are multiple buds, must be left undisturbed as it is the source of all new branch growth. Scions should be short enough to be stored in bags; 6"- 8" is a good length. Because the final graft should have only two or three buds, it is often possible to make more than one graft with a scion.

Uniting the Cambium Layers

Grafting is the uniting of the cambium layer of two compatible plants (fruits of compatible varieties in our case) such that they grow together. This requires some easy carpentry and some care so that the parts are kept alive until they grow together. One of the best ways to discover what the bark, wood, and cambium parts are, is to dissect a branch. Obtain a branch and observe its cross-section where it was cut off. Some types of branches may have a soft white core which is of little importance except that small branches which have it are somewhat more difficult to use for grafting. The hardwood material in the center is the wood and the outside material is the bark. Between the bark and the wood is the cambium; it is the thin (one cell) layer of tissue from which both new wood and new bark are formed. Peel some of the bark from the wood. If the branch is dormant the bark will be difficult to separate from the wood. When the tree is in full leaf and growing rapidly, the bark will separate from the wood very easily and the cambium will appear as a sticky wet film that covers the wood. When in the latter state, the bark is said to be "slipping." Remove the bark from an area having a bud and note the small protrusions in the wood at the bud location. If you use the single-bud variation of grafting called "budding," this portion of the wood or more must remain in the bud that is used.

Both bark grafts and budding require that the bark be separated from the wood. This is possible only when the bark is "slipping" during periods of active growth. This may require the storage of scion until late spring and one should check to see if the bark is slipping by making some small test cuts before getting too involved. Most other forms of grafting can be done to trees while either dormant or non-dormant. The persimmon is an exception and must be grafted after the stock plant has leafed out (mid-late April). Because heat can dry out the scion, grafting or budding is usually not done in the heat of summer.

 

S = Satisfactory for grafting.

u = Unsatisfactory for grafting, although grafts may grow for a time.

= Incompatible combination for grafting; the grafts either do not grow or growth is quite weak and short lived.

P Partly satisfactory for grafting. Most cultivars grow and fruit normally on this rootstock, although some cultivars and some trees do not make satisfactory or permanent graft unions.

P1 Some almond cultivars, such as Nonpareil, do not make a satisfactory union with Marianna 2624, so an interstock of Havens 26 plum must be used to work such cultivars on this stock. Other cultivars, such as Ne Plus Ultra and Mission, make reasonably satisfactory unions with Marianna 2624.

P2 Peach trees are short-lived and become dwarfed on almond rootstock.

P3 Many individual peach trees fail to grow well on apricot root-stock, but those that are successful make normal trees.

P4 Some pear cultivars, such as Bartlett, do not make good unions with quince, although other cultivars, such as Old Home and Hardy, do. Therefore, such cultivars as Bartlett are double worked, using one of the compatible cultivars.

P5 Some Japanese plum cultivars are compatible with some apricot seedlings. In contrast, most European plums are not compatible with apricot rootstocks.

* In general, many European and Japanese plums may be grafted on most European plums. Although many Japanese cultivars do well on other Japanese cultivars, European cultivars are not successful on Japanese stocks. Peaches, almonds, and apricots may sometimes be grafted on Japanese and European plums with reasonable success, but, as a rule the grafts either fail to grow or do not grow satisfactorily.

Reproduced with permission from the Division of Horticultural Sciences, University of California Leaflet 21103 entitled "Propagation of Temperate-Zone Fruit Plants

 

Razor-sharp Knife a Necessity

A very sharp knife is required for make the necessary cuts. Utility knives are popular because the blades are razor sharp and replaceable. Wrapping grafts can be successfully done with green or clear 1/2" nursery tape, budding rubbers or something similar. There are several wound-sealing compounds that are popular. One type is like very thick light-colored latex paint ("Tree Doc" brand or similar). Other types are the black tar-like compounds and grafting wax.

The budding rubbers are intended to deteriorate over a month or two and then fall off the tree. However, they will not deteriorate well if they are completely covered with the sealing compounds and other types of bindings may not deteriorate at all. In either case they should be checked in a month or two (longer if dormant) and removed before they constrict the scion and damage it. When applying the sealing compounds, one attempts to apply it only over the areas of the graft wound. For whip and similar grafts, this would leave about half the circumference of the scion still exposed to the air.

If properly stored, dormant scions can be kept alive for several months. To keep them from drying out, seal the cut ends by dipping them in melted wax. Then place the scions inside zip-lock freezer bags (other bags tend to leak) with a couple of drops of water and place them into the refrigerator. Bud orientation is also a prime consideration in choosing where to make the cuts on both the scion and main branch when grafting. Two or three buds are enough to produce branches and any excess length is an undesirable burden. Therefore, the grafted scion should consist of only two or three buds with the end bud pointing in the direction of desired growth.

Some Final Thoughts

Pomegranates, grapes, some berries, figs, mulberries, currants, citrons and kiwis can be grown by rooting cuttings in potting soil. Place them in the soil with one bud just above the surface and the remaining buds (two or more) in the soil. Keep the soil moist. It is difficult to tell the direction of the buds on grapes and figs, so their scions are cut with a slanting cut on the top and a square cut on the bottom. Most other fruit cuttings can not be rooted and can only be propagated by grafting or budding. The cuttings should be at least four buds and be approximately 12-14" long.

REFERENCES: (best listed first)

1. The Grafter's Handbook by Robert Garner (hardbound textbook dealing with grafting and the propagation of plants, rootstocks, etc.)

2. Propagation of Temperate-zone Fruit Plants,U.C. Cooperative Extension publication

3. Budding and Grafting Fruit Trees in the Home Garden, U.C. Cooperative Extension publication

4. Western Fruit Berries & Nuts by HP Books (largest listings of varieties and good grafting descriptions).

5. How to Grow Fruits, Nut & Berries by Sunset (good listings and grafting descriptions).

6. All About Growing Fruits & Berries by Ortho Books (the out-of-print 1976 edition is better than the new one).