Grafting
This is a method of plant propaga-tion in which a twig of one plant, called thescion, is made to grow on the roots of anotherplant, called the stock or the understock. Thescion is taken from the plant which is to bereproduced, and because this is an asexual meansof reproduction, the resulting plant will beidentical with the plant from which the scionwas taken if no shoots are allowed to grow onthe understock, or below the union of scion andunderstock.
In the first place, a scion and stock must be”compatible,” that is, they must be of a typethat will grow together, make a firm union andcontinue to grow afterwards. This is found outby experience, and the art of grafting is cen-turies old. One should not expect a scion ofMagnolia soulangiana to grow on apple or elmunderstock. In fact, it may not grow on all kindsof magnolia seedlings, but experience has shownthat it may be expected to grow best on under-stock of M. kobus or M. tripetala. Sometimesseveral species in the same genus are equallygood as understock, sometimes it has been foundit has been found that under certain conditionsone is better than another. English growers findthat Prunus serrula is easily compatible with P.avium understock, while some Americangrowers have better success with P. sargentiiunderstock.
In the grafting operation the theory is to placethe living cambium tissue of scion and under-stock in contact with each other. This is simply
done by making the proper kind of cut into theunderstock and gently slipping the whittledscion into it. This operation must be done whenboth scion and understock are about ready foractive growth. Actually, it is a greenhouseoperation where the understock, in a pot, hasalready been forced into active growth and thescion is yet dormant. Usually Feb. or March isgrafting time indoors.
As soon as the scion and stock arc slippedtogethcr, they are bound tightly in place toprevent movement between them. Flat rubberbands are specially made for this and are idealsince they can be bound just tight enough tohold the a together, but loose enough to thatthe rubber will give a little as the new graftincreases in circumference. This “tie” remains_on for a few months until stock and scion haveclosely knit, when it is simply cut and left onthe union to eventually fall off.
Grafting is also done out of doors at a timejust before vigorous growth commences on theunderstock. This is usually confined to treesthat are being “made over” as will be explainedbelow. Grafting small plants out of doors doesnot result in as much success as doing it insideunder controlled temperature and moistureconditions.
Factors other than timing must be right. Airtemperature must be in the 70′s or conduciveto continued plant growth. Moisture must bepr.ent‚Äîthe graft union mast not bc allowed todry out in any way. Disease spores must notget into the union. These are the reasons whygrafting is usually carried out in the greenhousein “grafting cases,” places enclosed by glass orpolyethylene with high humidity. This is alsothe reason why the graft union is covered withwax or polyethylene film as soon as it is madeto keep the tender new-forming cells fromexposure and possible drying out.
The most difficult time for the new graft iswhen it is noted that the scion has started intoactive growth. It must be kept in active growth,yet too high a temperature and too muchmoisture in the grafting case may cause it togrow too rapidly and fail to make a properunion. Here experience certainly aids theindividual in properly regulating moisture andtemperature.
The most important decision to make ingrafting is to select the right kind of graft cutto make. Actually, if properly done, any oneof the methods should result in a successfulgraft, but experience has shown that certaintypes of grafting cuts seem to result in better endr.ults on certain species than ashore. This isnot the place to go into this detailed discussion,but one should be familiar with the differenttypes.
Whip Graft
A double matching cut is made in both stockand scion. If this is to be used, the understockand the scion should be about the same dia.(lead-pencil size or slightly larger) and the topof the stock should be completely cut off aninch or so above the place of the proposedunion. The whip graft is also ideal to use in rootgrafting, that is, in grafting a scion on to a pieceof root (of the same dia.). If done properly, andit takes experience to make just the right cuts,it can be highly successful because there is somuch of the cambium that can be fitted togetherin this double cut.
Side Graft
Merely making a slanting cut into the stock
and inserting a wedge-shapcd scion into it. Thisis often the method chosen when thc stock islarger in dia. than the scion. Sometimes the topof the stock is severed just above the graft assoon as it is made. Other times it is left to growfor a week or two and then cut off. It is thismethod which is frequently used in bonsaiculture to supply a new branch at exactly theright place it is needed.
Cleft Graft
This is the type of graft employed in graftingtrees in the open. It is frequently employed ingrafting apples, where a tree of an old out-moded variety is to be “changed over” to a newand better variety. In this case, all the mainlimbs are sawed off carefully and “clefts” or splits are made in them with a large graftingtool similar to a butcher’s knifc. Two or 3 suchopenings can be made in a 4-6 in. branch. Then,3 or more wedge-shaped scions are insertedcarefully, so the cambium tissue of stock andscion meet exactly, the entire union is paintedwith wax and one then awaits developments.Only of the 3 or 4 scions will be allowed togrow eventually, but it is a quick method ofmaking over a tree of bearing size. In fact, thenewly made-over tree may grow so well that itmay begin producing the new variety of applein 3 or 4 years. Because the stock is so large, itis not necessary to tie stock and scion togetherin such a graft, for the properties inherent inthe wood of the large branches are enough tohold the scions tightly for all practical purposes.
Bark Graft
This is done on the cut limbs of trees, merelyby slitting the bark a few inchos in a straightline from the cut surface, and then inserting thewedge-shaped scion just between the bark andwood of the stock. Three or 4 of these can beinserted, but the whole should be tied tightly toprevent the bark of the branch from curlingaway or splitting farther and thus exposing thescion to drying out.
Approach GraftingConsider z small plants in pots, one of a veryrare type, the other a worthless seedling. The
seedling would act as the undcrstock for therare plant, the whole idea being that one doesnot risk loss of the rare plant in this method. Acut is made in the side of the understock or someof thc bark is very carefully removed just to thecambium. A matching cut is made in the rareplant or a matching part of its bark is carefullyremoved. Then they are joined together, tied andpainted, while the tops of both are allowed togrow. If it is obvious that the union is growingtogether, the part of the undcrstock above thegraft can be removed. When the union issolidly made, the scion material can be partiallycut away from the scion plant, and later anotherdeeper cut made so that the severance of thescion from the parent plant takes place over aperiod of weeks. This is a method used by theexperts to graft two plants together that areotherwise difficult.
lnarching
Sometimeo a plant is growing with the wrongkind of understock and the tree needs a betterroot system. Young plants arc established at thebase, a narrow strip of bark removed on the1000 10 correspond with a similar width of barkremoved on the new plants. Several such plantscan be stabilized and grafted 00 000 trunk.
Bridge GraftingFrequently used in the case of a tree that hasbeen completely girdled by rodents or byaccident. The bark of the tree is cleaned off to smooth straight lines, several twigs of the propersize and length are cut from the tree itself andinserted under the bark of the tree in the samemanner as any bark graft, above and below itspart with injured bark. The bridge grafts can benailed or tied in place and the whole exposedwound painted with wax. The idea here is to cutthe top and bottom of the scions in such a waythat they can be inserted underneath the barkabove and below the wound, with the cambiumtissues of stock and scion in contact with eachother. Hence those shoots will, if they grow, actas bridges over the injured trunk for the upwardand downward flow of nutrients and foods.Many a damaged tree has been saved in thisway. However, such an operation is bast donewhen the tree is dormant, certainly not whenthe scions are in leaf. If properly done, thesescions will gradually increase in size and maycompletely heal over the injured trunk bygrowing solidly together.
Double GraftingSometimes this method is used, especially toproduce a dwarf plant or when one kind ofplant material is not compatible with the under-stock. Grafting is done in the normal way usingan “intermediate” scion, that is, a scion from aplant that will be compatible with the under-stock and the plant to be grafted as well. An example is the grafting of Bartlett Pear onquince roots for dwarfing. These 2 are notcompatible but if a seedling pear is grafted onthe quince roots, then the Bartlett Pear graftedon the seedling pear, this results in a good tree.This can be done in different ways. The BartlettPear can be grafted on pieces of the seedlingpear and the grafted pieces put in moistenedpeat moss in a cool place fore few weeks untilcallused, when this piece (with scion and inter-mediate graft) is grafted onto a dormant quinceroot. Or, the seedling pear can be budded onto toted cuttings of the quince one summer,then the Bartlett Pear can be budded on theseedling pear the next.
So, grafting can be a complicated processbut, if done properly, results in fairly good trees.Sometimes, years after the grafting, one noticesa large hump at the graft union, showing clearlythat the stock has grown much faster than thescion. Sometimes just the reverse is true.Frequently this is not serious but, wheneverpossible, it is always best to select an understockthat grows at the same rate as the plant fromwhich the scion was taken
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