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Grafting and Budding Nursery
Crop Plants
AG-396
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Grafting
When to Graft
Unlike budding, which can be performed before or
during the growing season, most grafting is done during winter and
early spring while both scion and rootstock are still dormant.
Containerized plants may be moved indoors during the actual grafting
process; after grafting, these plants are placed in protected areas
or in unheated overwintering houses. Field-grown stock, of course,
must be grafted in place. Some deciduous trees are commonly grafted
as bare rootstock during the winter and stored until spring planting.
Indoor winter grafting is often referred to as bench grafting because
it is accomplished at a bench.
Selecting and Handling Scion Wood
The best quality scion wood usually comes from
shoots grown the previous season. Scions should be severed with
sharp, clean shears or knives and placed immediately in moistened
burlap or plastic bags. It is good practice during the harvesting of
scions and the making of grafts to clean the cutting tools regularly.
This may be done by flaming or immersing them in a sterilizing
solution. Isopropyl (rubbing) alcohol also works well as a sterilant,
although it evaporates quite readily. An alternative sterilizing
solution may be prepared by mixing one part household bleach with
nine parts water (by volume). However, this bleach solution can be
highly corrosive to certain metals.
For best results, harvest only as much scion wood
as can be used for grafting during the same day. Select only healthy
scion wood that is free from insect, disease, or winter damage. Be
sure the stock plants are of good quality, healthy, and true to type.
Scion wood that is frozen at harvest often knits more slowly and in
lower percentage. If large quantities of scion wood must be harvested
at one time, follow these steps:
- Cut all scions to a uniform length, keep their basal ends
together, and tie them in bundles of known quantity (for example,
50 scions per bundle).
- Label them, recording the cultivar, date of harvest, and
location of the stock plant.
- Wrap the base of the bundles in moistened burlap or sphagnum,
place them in polyethylene or waterproof paper bags, and seal the
bags.
- Store the bundles for short periods, if necessary, either iced
down in insulated coolers or in a commercial storage unit at
32o to 34oF.
- Never store scions in refrigerated units where fruits or
vegetables are currently kept or have been stored recently. Stored
fruits and vegetables release ethylene gas, which can cause woody
plant buds to abort, making the scions useless.
- Keep the scions from freezing during storage.
NOTE: In grafting, as well as budding, the vascular cambium of
the scion or bud must be aligned with the vascular cambium of
rootstock. In woody plants the cambium is a very thin ribbon of
actively dividing cells located just below the bark. The cambium
produces conductive tissue for the actively growing plant (Figure 1).
This vascular cambium initiates callus tissue at the graft and bud
unions in addition to stimulating tissue growth on the basal ends of
many vegetative cuttings before they have rooted.
Figure 1. Cross section of a woody plant stem.
Types of Grafts
Nurserymen can choose from a number of different
types of grafts. This section describes only those basic types of
grafts used on nursery crop plants.
Cleft Graft
One of the simplest and most popular forms of
grafting, cleft grafting (Figure 2), is a method for top working both
flowering and fruiting trees (apples, cherries, pears, and peaches)
in order to change varieties. Cleft grafting is also used to
propagate varieties of camellias that are difficult to root. This
type of grafting is usually done during the winter and early spring
while both scion and rootstock are still dormant. Cleft grafting may
be performed on main stems or on lateral or scaffold branches.
The rootstock used for cleft grafting should range
from 1 to 4 inches in diameter and should be straight grained. The
scion should be about 1/4 inch in
diameter, straight, and long enough to have at least three buds.
Scions that are between 6 and 8 inches long are usually the easiest
to use.
Figure 2. Cleft graft.
Preparing the Rootstock. The stock should be
sawed off with a clean, smooth cut perpendicular to the main axis of
the stem to be grafted. Using a clefting tool wedge and a mallet,
make a split or "cleft" through the center of the stock and down 2 to
3 inches. Remove the clefting tool wedge and drive the pick end of
the tool into the center of the newly made cleft so that the stock
can be held open while inserting the scion.
Preparing the Scion. In cleft grafting, one
scion is usually inserted at each end of the cleft, so prepare two
scions for each graft. Select scions that have three or four good
buds. Using a sharp, clean grafting knife, start near the base of the
lowest bud and make two opposing smooth-tapered cuts 1 to 2 inches
long toward the basal end of the scion. Cut the side with the lowest
bud slightly thicker than the opposite side. Be sure the basal end of
the scion gradually tapers off along both sides.
Inserting the Scion. Insert a scion on each
end of the cleft, with the wider side of the wedge facing outward.
The cambium of each scion should contact the cambium of the
rootstock.
Securing the Graft. Remove the clefting tool
from the cleft so that the rootstock can close. Pressure from the
rootstock will hold the scions in place. Thoroughly seal all cut
surfaces with grafting wax or grafting paint to keep out water and
prevent drying. If both scions in the cleft "take," one will usually
grow more rapidly than the other. After the first growing season,
choose the stronger scion and prune out the weaker.
NOTE: The temperature of grafting wax is
critical. It must be hot enough to flow but not so hot as to kill
plant tissue. Recently, paint-like sealants have replaced wax in many
areas because they are easier to use and require no heating.
Bark Graft
Bark grafting (Figure 3) is used primarily to top
work flowering and fruiting trees. In contrast to cleft grafting,
this technique can be applied to rootstock of larger diameter (4 to
12 inches) and is done during early spring when the bark slips easily
from the wood but before major sap flow. The rootstock is severed
with a sharp saw, leaving a clean cut as with cleft grafting.
Figure 3. Bark graft.
Preparing the Stock. Start at the cut
surface of the rootstock and make a vertical slit through the bark
where each scion can be inserted (2 inches long and spaced 1 inch
apart).
Preparing the Scion. Since multiple scions
are usually inserted around the cut surface of the rootstock, prepare
several scions for each graft. Cut the base of each scion to a 1
½- to 2-inch tapered wedge on one side only.
Inserting the Scion. Loosen the bark
slightly and insert the scion so that the wedge-shaped tapered
surface of the scion is against the exposed wood under the flap of
bark. Push the scion firmly down into place behind the flap of bark,
replace the bark flap, and nail the scion in place by driving one or
two wire brads through the bark and scion into the rootstock. Insert
a scion every 3 to 4 inches around the cut perimeter of the
rootstock.
Securing the Graft. Seal all exposed
surfaces with grafting wax or grafting paint. Once the scions have
begun to grow, leave only the most vigorous one on each stub; prune
out all the others. Bark grafts tend to form weak unions and
therefore usually require staking or support during the first few
years.
Side-Veneer Graft
At one time the side-veneer graft (Figure 4) was a
popular technique for grafting varieties of camellias and
rhododendrons that are difficult to root. Currently, it is the most
popular way to graft conifers, especially those having a compact or
dwarf form. Side-veneer grafting is usually done on potted
rootstock.
Figure 4. Side veneer graft
Preparing the Stock. Rootstock is grown in
pots the season before grafting, allowed to go dormant, and then
stored as with other container nursery stock. After exposure to cold
weather for at least six weeks, the rootstock is brought into a cool
greenhouse for a few days before grafting takes place to encourage
renewed root growth. The plant should not be watered at this
time.
Make a shallow downward cut about 3/4 inch to 1
inch long at the base of the stem on the potted rootstock to expose a
flap of bark with some wood still attached. Make an inward cut at the
base so that the flap of bark and wood can be removed from the
rootstock.
Preparing the Scion. Choose a scion with a
diameter the same as or slightly smaller than the rootstock. Make a
sloping cut 3/4 to 1 inch long at the base of the scion. (Use the
bark grafting technique shown in Figure 3.)
Inserting the Scion. Insert the cut surface
of the scion against the cut surface of the rootstock. Be certain
that the cambia contact each other.
Securing the Graft. Hold the scion in place
using a rubber grafting strip, tape, or grafting twine. Seal the
entire graft area with warm grafting wax or grafting paint. Remove
the rubber or twine shortly after the union has healed. Never allow
the binding material to girdle the stem.
Splice Graft
Splice grafting (Figure 5) is used to join a scion
onto the stem of a rootstock or onto an intact rootpiece. This simple
method is usually applied to herbaceous materials that callus or
"knit" easily, or it is used on plants with a stem diameter of 1/2
inch or less. In splice grafting, both the stock and scion must be of
the same diameter.
Figure 5. Splice graft.
Preparing the Stock and Scion.Cut off the
rootstock using a diagonal cut 3/4 to 1 inch long. Make the same type
of cut at the base of the scion.
Inserting the Scion. Fit the scion to the
stock. Wrap this junction securely with a rubber grafting strip or
twine.
Securing the Graft. Seal the junction with
grafting wax or grafting paint. Water rootstock sparingly until the
graft knits. Over watering may cause sap to "drown" the scion. Be
sure to remove the twine or strip as soon as the graft has
healed.
Whip and Tongue Graft
The whip and tongue technique (Figure 6) is most
commonly used to graft nursery crops or woody ornamentals. Both the
rootstock and scion should be of equal size and preferably no more
than 1/2 inch in diameter. The technique is similar to splice
grafting except that the whip on the rootstock holds the tongue of
the scion in place (and vice versa). This leaves both hands free to
wrap the joint.
For the whip and tongue graft, make similar cuts on
both the stock and scion. These cuts should be made with a single
draw of the knife and should have a smooth surface so that the two
can develop a good graft union. Up to this point, rootstock and scion
are cut the same as for a splice graft.
Figure 6. Whip and tongue graft.
Preparing the Stock and Scion. Cut off the
stock using a diagonal cut. The cut should be four to five times
longer than the diameter of the stock to be grafted. Make the same
kind of cut at the base of the scion.
Next, place the blade of the knife across the cut
end of the stock, halfway between the bark and pith (on the upper
part of the cut surface). Use a single knife stroke to draw the blade
down at an angle through the wood and pith. Stop at the base of the
initial diagonal cut. This second cut must not follow the grain of
the wood but should run parallel to the first cut.
Inserting the Scion. Prepare the scion in
the same way. Fit the scion into the rootstock so that they interlock
whip and tongue. Be certain that the cambia are aligned.
Securing the Graft. Wrap the junction with a
grafting strip or twine, and seal it with grafting wax or grafting
paint. Never allow the binding material to girdle the stem.
Saddle Graft
Saddle grafting (Figure 7) is a relatively easy
technique to learn and once mastered can be performed quite rapidly.
The stock may be either field-grown or potted. Both rootstock and
scion should be the same diameter. For best results, use saddle
grafting on dormant stock in mid- to late winter. Stock should
not be more than 1 inch in diameter.
Figure 7. Saddle graft.
Preparing the Stock. Using two opposing
upward strokes of the grafting knife, sever the top from the
rootstock. The resulting cut should resemble an inverted V, with the
surface of the cuts ranging from 1/2 to 1 inch long.
Preparing the Scion. Now reverse the
technique to prepare the base of the scion. These cuts on the
rootstock and scion must be the same length and have the same slope
so that a maximum amount of cambial tissue will make contact when the
two halves are joined.
Inserting the Scion. Place the V-notched
scion onto the saddle of the rootstock. If rootstock and scion are
the same diameter, cambial alignment is easier; otherwise adjust as
needed.
Securing the Graft. Wrap the graft with a
grafting twine, tape, or strip, then seal it with grafting wax or
grafting paint.
All of the preceding techniques are used to top
work horticultural crops for a particular purpose. Occasionally,
however, grafting is used to repair injured or diseased plants. Two
common techniques available for this purpose are bridge grafting and
inarch grafting.
Bridge Graft
Bridge grafting (Figure 8) is used to "bridge" a
diseased or damaged area of a plant, usually at or near the base of
the trunk. Such damage commonly results from contact with grading or
lawn maintenance equipment, or it may be caused by rodents, cold
temperatures, or disease organisms. The bridge graft provides support
as well as a pipeline that allows water and nutrients to move across
the damaged area.
Bridge grafts are usually done in early spring just
before active plant growth begins. They may be performed any time the
bark on the injured plant "slips."
Figure 8. Bridge graft.
Preparing the Scion. Select scions that are
straight and about twice as long as the damaged area to be bridged.
Make a 1 1/2- to 2-inch-long tapered cut on the same plane at each
end of the scion.
Preparing the Stock. Remove any damaged
tissue so the graft is on healthy stems. Cut a flap in the bark on
the rootstock the same width as the scion and below the injury to be
repaired. Gently fold the flap away from the stock, being careful not
to tear the bark flap.
Inserting the Scion. First, insert and
secure the scion below the injury; push the scion under the flap with
the cut portion of the scion against the wood of the injured stem or
trunk. Then go back and insert and secure the scion above the injury
following these same steps. Push the scion firmly into place. Pull
the flap over the scion and tack it into place as described for bark
grafting (Figure 3).
When grafting with young stems that may waver in
the wind, insert the scions so that they bow outward slightly. Bridge
grafts should be spaced about 3 to 4 inches apart across the damaged
area.
Securing the Graft. Secure all graft areas
with warm grafting wax or grafting paint. During and after the
healing period, remove any buds or shoots that develop on the
scions.
Inarch Graft
Inarching, like bridge grafting, is used to bypass
or support a damaged or weakened area of a plant stem (Figure 9).
Unlike bridge grafting, the scion can be an existing shoot, sucker,
or watersprout that is already growing below and extending above the
injury. The scion may also be a shoot of the same species as the
injured plant growing on its own root system next to the main trunk
of the damaged tree. With the inarching technique, the tip of the
scion is grafted in above the injury using the same method as for
bark or bridge grafting.
Figure 9. Inarch graft.
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