University of Missouri Extension

G6971, Reviewed December 2008

Grafting
 

Common terms

  • Scion
    A piece of detached twig or shoot. The scion usually contains two or three buds, although it may contain more. When the scion is only a single bud, the form of grafting is known as budding.
  • Rootstock (also stock or understock)
    This is a term applied to the part of the graft that produces the root system of the grafted plant.
  • Interstock (also interstem)
    This is a piece of plant (usually to form trunk or
    a portion of it) grafted between the scion and understock.
  • Cultivar
    This is a term now used in place of variety. It means cultivated variety
    and differentiates a plant from a botanical or natural variety.
  • Cambium
    This is a single layer of cells between the wood and bark of a tree or shrub that produces new cells. In graftage, the cambium of the scion must line up as closely as possible with the cambium of the stock for a good union.
Ray R. Rothenberger and Christopher J. Starbuck
Department of Horticulture

Grafting is the act of joining two plants together. The upper part of the graft (the scion) becomes the top of the plant, the lower portion (the understock) becomes the root system or part of the trunk. Although grafting usually refers to joining only two plants, it may be a combination of several. A third plant added between two others becomes the trunk or a portion of it. This is called an interstem. Multiple grafts may produce an apple tree with several varieties or a rose-of-Sharon shrub with several different colors of flowers.

Why graft?

Some cultivars (varieties) of plants do not come true from seeds. Others are difficult or impossible to reproduce from cuttings or other propagation techniques. Grafting (topworking) is a way to change a large tree from an old to a new variety. It is also a method of using a root system better adapted to soil or climate than that produced naturally by an ungrafted plant. By using special understocks or interstems, grafting is a way to produce dwarf plants.

What are the limitations?

Not all plants can be grafted. Generally, only plants closely related botanically form a good graft union. Grafting is not a means of developing new varieties. The stock and scion must be compatible. Incompatible grafts may not form a union, or the union may be weak. A poor union results in plants that either grow poorly, break off or eventually die.

The compatibility of plants has been determined through many years of trial. There is no other way to determine whether or not two plants will produce a good graft union. This publication will help you make a decision about the possibility.

Reasons for failure

  • Stock and scion were not compatible.
  • The cambiums were not meeting properly.
  • Scions were upside down.
  • Grafting was done at the wrong time.
  • Understock or scion were not healthy.
  • Scions were dried out or injured by cold.
  • Scions were not dormant.
  • The graft was not properly covered with grafting wax.
  • The scion was displaced by storm, birds or other means.
  • The graft was shaded too much by other growth.
  • The graft was attacked by insects or disease.
  • The graft union was girdled because tape was not cut or released in time.

What can be grafted?

Most varieties of a particular fruit or flowering species are interchangeable and can be grafted. Because of differences in vigor, some are better able to support others as understocks. For example, although a union is possible, sour cherry is not a good understock for sweet cherry. Sweet cherry is more commonly grafted onto Mazzard (Prunus avium) or Mahaleb (P. mahaleb) seedlings.

Plants of the same botanical genus and species can usually be grafted even though they are a different variety. Plants with the same genus but of a different species often can be grafted. But the result may be weak or short-lived, or they may not unite at all.

Plants of different genera are less successfully grafted, although there are some cases where this is possible. For example, quince, genus Cydonia, may be used as a dwarfing rootstock for pear, genus Pyrus.

Plants of different families cannot be grafted successfully. Although it has been reported that relatively short-lived grafts of herbaceous plants of different families have been made, there is no successful practice for commercial or home grafting of woody plants of different families.

It is sometimes believed that two plants can be made into a genetically different plant by the process of grafting. However, there is no basis for this idea. Although there are cases where a different type of shoot develops from the graft union, this is the result of a chimera, a type of mutation. This is not a true intermingling of the genetic structure of two different plants as occurs in seed-produced hybrids.

When is the time to graft?

Most grafting is done in late winter or early spring before new growth begins. The best time is after the chance of severe cold has passed but well before hot weather arrives. Scion wood may be collected during the winter. Store it in a cold, moist place at temperatures close to 34 degrees Fahrenheit. At home, a few scions could be stored in a plastic bag in the refrigerator with moist paper towels, or they could be dipped in paraffin so they retain moisture.

What materials are needed?

What grafting technique?

Grafting techniques can be divided into two basic types, which are largely determined by the size of the understock. In some cases, a graft may be made to join a scion and understock of nearly equal size. The other type attaches a small scion to a much larger understock. In this case, several scions may be attached to the understock as in cleft or bark grafting.

Figure 1
Whip graft

Whip graft cuts A. Cuts for the whip graft must be smooth and straight.
 

Form the tongueB. Cut again to form the tongue.
 

Push stock and scion tightly togetherC. Push stock and scion tightly together.
 

Wrap graftAttached to root systemD. Wrap graft to keep cuts tight and to prevent drying.

E. Whip and tongue graft with scion attached to root system.
 

Grafts with similar scion and understock sizes

Whip graft, bench graft
The whip graft (Figure 1) is fairly easy and heals rapidly. It works best when the stock and scion are of similar diameter, preferably between 1/4 and 1/2 inch.

The stock can be either a plant growing in the field or a dormant bareroot plant as in a bench grafting. The stock should be smooth and straight-grained. Do not graft near a point where side twigs or branches have developed.

The scion should be 1-year-old wood, preferably the same size as the stock. If the stock is larger than the scion, contact can be made on only one side. The scion should never be larger than the stock.

Figure 2
Cleft graft

Cut stock smoothlyOpen with a grafting toolA. Cut stock smoothly. Trim any rough edges with a knife.

B. Split stock, and open with a grafting tool.
 

Prepare scionMake a pie-shaped wedge C. Make a long, smooth cut to prepare scion.

D. Cut again to make a pie-shaped wedge.
 

Promptly insert scion E. Promptly insert scion into stock after cutting.
 

Cambium layers must match

F. Cambium layers must match closely.
 

 

Slight slant can ensure cambial contact Wax thoroughly Shorten one scion G. A very slight slant can ensure cambial contact.

H. After insertion, wax thoroughly to prevent drying.

I. After the first year, shorten one scion to allow the other to develop.
 

Grafts with small scions and large understocks

The cleft graft
The cleft graft (Figure 2) is most commonly used to topwork a tree; that is, to change from one variety to another. It can be used on either young or mature trees. Young trees may be cleft grafted on the trunk, while older trees are grafted on branches not more than 2-1/2 inches in diameter. Branches fully exposed to sunlight and in the main stream of sap flow are more successful than those in shaded or inactive areas. Grafts on upright branches grow better than those on horizontal branches.

Figure 3
Bark graft

Single cut or a double cut Form a shoulder Making a tight fit A. Stock may be prepared with a single cut, left, or a double cut.

B. Cut scion to form a shoulder.

C. For single cut, left, insert scion under bark, making a tight fit. For double cut, use small nails to secure scions.
 

Bark graft (veneer graft)
Bark grafting (Figure 3) is relatively easy and requires no special tools. It is similar to cleft grafting and may be performed on branches ranging from 1 inch to several inches in diameter.

Figure 4
Side graft

Cut scion Make a slanting cut Insert scionCut off the top A. Cut scion to form a short, smooth edge.

B. Make a slanting cut into the stock.

C. Insert scion so that cuts on thicker side match the cambium of the stock.

D. Cut off the top of the stock only after growth begins.
 

Side graft, stub graft
The side graft is relatively simple and is suitable for plants that are too large for a whip graft but not large enough for cleft or bark grafts (Figure 4). The plant or branch that will serve as the stock should be between 1 and 2 inches in diameter. The material for the scion should be about 1/4 inch in diameter.

Grafting tips

Scion
Scion wood should always be dormant. Scion wood should be made from previous season's growth and have a diameter of 1/4 to 3/8 inch. Store the scion in moist sphagnum moss, sand or a plastic bag in a cool place. It must be kept moist and cool until used. After the cuts are made, scions must be inserted immediately, or cuts should be kept moist until used.

Scion wood should be made of twig sections with two to three buds each. Discard the tip of scion wood and recut the base before grafting.

Timing
The best time for grafting is in the spring just as growth starts. When necessary, grafting can start several weeks before growth is expected and can continue a few weeks after growth has started, if you have dormant scion wood in storage and if weather is not exceptionally warm.

Other suggestions
The stock and scion must have cambial contact for union and growth to take place. All cut surfaces must be covered and kept covered with grafting wax until complete healing has occurred. In a few techniques, alternate methods for maintaining moisture in the union are used. But if you are grafting only a few plants, you will find waxing the graft most satisfactory.

After the graft has taken and growth has started, cut off any side shoots or competing twigs that would shade or compete with the development of the new graft.

Banana graft Link to 600k wav file Audio clip 1
The banana graft can be used for slightly older plants where stock and scion are about the same size. The stock is peeled as shown and the wood is cut.
 

Wood removed Link to 600k wav file Audio clip 2
Here the wood has been removed from the stock and is ready to receive the scion, which is being prepared.
 

Whip-and-tongue grafting Link to 600k wav file Audio clip 3
Apple plants joined by whip-and-tongue grafting.
 

Wrap to keep the union tight Link to 600k wav file Audio clip 4
After the stock and scion are fitted together, they are wrapped to keep the union tight and moist. After healing through the winter, they will be ready for the field by spring.
 

Cleft graft Link to 600k wav file Audio clip 5
For a cleft graft, where the stub is split, two scions are normally used.
 

Bark grafting Link to 600k wav file Audio clip 6
This scion of pecan being prepared for bark grafting will be fit on a section of the 1-1/2-inch pecan seedling rootstock that has been cleared of bark.
 

Cover the union Link to 600k wav file Audio clip 7
After completing the grafting process, promptly cover the union to keep the graft cool and moist.


 

 

G6971, reviewed December 2008

G6971 Grafting | University of Missouri Extension

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