Grafting is a fascinating subject. Be it of bone or skin, done by a surgeon, or grafting to save your injured tree or plant, as practiced by the gardener. The objectives are often comparable.
Horticultural grafting is a valuable way of propagating plants – tree fruits or roses. Grafting can also help repair injuries brought about by disease or mechanical means.
The home gardener may make a graft to save a cherished tree whose trunk has been injured.
Still, without a thorough understanding of the procedure, it may be advisable to obtain the help of a professional tree surgeon.
Remedial Grafting For Breeding Hybrids
One of the most interesting applications of remedial grafting has been in chestnut breeding work.
Dr. Arthur Harmount Graves has been engaged in breeding chestnuts to obtain a blight-resistant tree as valuable for timber as our native chestnut was before it was decimated by blight.
To this end, crosses were made between Oriental species and our own native chestnut.
The first generation of Japanese-American trees indicated that the American species was dominant but that the hybrid, though to a lesser degree than the American species, was susceptible to blight.
It was, therefore, necessary to continue breeding for segregation and a combination of the desired characters.
The problem then was how to keep these hybrids alive until flowering so that further crossing could be made.
Dr. Graves solved this problem by putting into practice a method of “in-arching,” which would bridge the gap made between healthy root and healthy top by the lesion caused by the fungus.
Fortunately, blighted chestnuts send out shoots from below the lesion, providing suitable material to be grafted by uniting them in the healthy trunk or branch above the lesion.
Grafting Methods
In the Northern Nut Growers Association annual report, Dr. Graves described the method he used.
Briefly, it is as follows:
- An incision is made in the shape of an inverted T in healthy bark above the lesion.
- A “half-moon” sliver of bark is cut below the inverted T to the horizontal part.
- A sucker is cut off at a point a little longer than is necessary to reach the T, and its top is cut to a long sharp wedge.
- The bark flaps adjacent to the horizontal part of the cut are gently lifted from the wood.
- The scion is bent outward, and the wedge is forced between bark and wood.
- Then the parts are tied in place with soft cotton twine.
- The wound covered with melted paraffin heated no more than is enough to bring it to the melting point.
Dr. Graves finds that the best time to operate in southern Connecticut is April or early May.
Possibly the job could be done any time when bark lifts readily, say in July and early August.
Combinations Of Grafting Methods
Another application of the method was to be seen on an elm growing on the campus of the University of Wisconsin.
This elm encircled at the base and therefore in a dying condition, was saved by the ministrations of a tree surgeon.
In this case, elm saplings were planted around the tree and their tops grafted into its trunk.
These methods are a combination of “in-arching” or approach grafting, a seldom-used means of propagating difficult plants, and true bridge grafting used by orchardists to restore the connection between top and roots when rodents have girdled young trees during the winter.
In this latter case, young shoots of the affected tree are sharpened at both ends and inserted beneath the bark above and below the injured portion of the trunk.