Texas Inlay Bark Graft
Larry A. Stein, Ph.D. and Julian W. Sauls, Ph.D.
Professor and Extension Horticulturists
Texas Cooperative Extension
Inlay grafting is one of the best and most popular systems of propagating pecans in Texas. It has been successfully used when other systems have failed because of heat, drought and wind. It has also been successfully used on walnuts, apples, pears, grapes, rabbiteye blueberries, persimmons, citrus, avocados and mangos.
The Texas method of inlay grafting, developed by B.G. Sitton, L.D. Romberg, F.R. Brison, B.G. Hancock and others in the 1950's, follows the basic fundamentals of the standard bark graft. However, this technique uses an inlay cut and employs an entirely new system of covering the graft and stock. The inlay occurs when two parallel cuts are made through the stock bark forming a scion inlay pattern on the stock. Aluminum foil is used as a stock cover, reflecting sunlight and reducing temperatures around the graft. The foil is covered with polyethylene film to assure constant high relative humidity around the graft. This system not only results in a high percentage of growing grafts, but it is easy to use. The more stressful the grafting conditions, the more important this grafting technique becomes.
The ideal time to inlay graft is in early spring to about the end of May. Although the technique can be used into the summer, success is limited due to increasing heat. Bark slippage is a must for inlay grafting, which is usually indicated by tree growth and leaves. To ascertain that the bark is slipping, select a point above where you anticipate inserting the graft. Make a narrow, V-shaped pair of cuts completely through the bark, then use the knife point to lift the bark inside the point of the V. Gently peel the bark up and away from the wood--if it comes cleanly and easily, the bark is slipping and you can proceed with the graft. If not, wait a week or so and check again.
Anyone can successfully use the inlay graft by following these instructions and practicing to develop skill in the basic techniques. The key is to practice, as you may be "all thumbs" the first few times you try to graft. In this presentation, 32 images are included to illustrate the finer points of the technique. Each image is shown with the text as a thumbnail version for speed of downloading. Click on the thumbnail image to see it as a full screen version, then click "Back" to return to the text and thumbnails.
|Tools used in pecan propagation.||Seedling pecan tree to be grafted.|
Necessary equipment includes dormant graftwood, aluminum foil, polyethylene bags, a sharp knife, 18 gauge 3/4-inch nails, hammer, budding tape, shears, saw and glue. All necessary equipment can be carried in an apron.
Use rootstock trunks or major side limbs that are 1½ to 3 inches in diameter. On larger trees, leave one or two side branches below the graft to keep the tree vigorous, to protect from sunburn and to keep the graft from overgrowing and blowing out, as blow outs seem to be more common on larger trees than on smaller ones.
|Top view of stock showing flat side at left.||Trimming the stock cut.|
Cut straight across the trunk or limb with a sharp saw above a smooth, even section of the trunk or limb. Make the cut 7 or 8 feet above ground if livestock or deer have access to the trees. Select a section of stock with a flat surface so that the flat side of the graft stick will fit snugly in the inlay without air space separation. If possible, choose a flat spot on the south or southwest side so that prevailing winds will blow the graft shoot toward the trunk instead of away from it. If there is not a suitably flat surface at the cut, you can always cut the stock off again a few inches further down.
General clean up of the saw cut can be made with a knife. This is always done when a chain saw is used to cut off the tree top or limb. Normally this clean up is performed all around the stock, but it can be limited to just the area where the graft will be placed.
|Rough bark pared down for grafting.||Typical pecan graft stick.|
If the bark is rough, pare it down to live bark, forming a clean shield. Leave the bark as thick as possible to securely hold the graft. Do not cut into the wood.
A smooth, straight graft stick with 3 or 4 plump buds should be selected. The size of the graft wood should be selected for the size of the stock to be grafted. Use 3/8-inch diameter graft wood for trees up to about 2 inches in diameter, and 1/2-inch diameter graft wood for larger trees.
|Cut off the base of the graft stick.||Beginning the long cut on the graft stick.|
The end of the base of the graft stick should be cut off before preparing the scion (graft) for placement on the tree, regardless of whether the wood was sealed with wax or shellac.
Use a knife with a very sharp blade similar to that illustrated. Grafting knife blades are beveled on only one side so as to enable making a flat cut. Firmly hold the knife in a closed fist. Start just below the insurance bud or the lowest bud on the graft stick and cut the graft stick with several long, thin slices to reach the center of the stick. The finished graft stick will have one to three buds and three cuts; a slant cut, a long cut and a back cut.
The slant cut should begin 1/2 inch below and on the side opposite the lowest bud. It should extend half the distance through the graft stick at approximately a 45 degree angle.
|Halfway through the long cut.||Completed long cut.|
The long cut is essentially right down the middle of the wood between the slant cut and the end of the graft stick. It must be perfectly flat at the center of the graft stick and 1.5 to 3 inches long.
|The back or chisel cut.||Side view of the finished scion.|
The back cut creates a chisel-shaped point about half an inch long on the opposite side and lower end of the graft stick. This makes it easier to insert the graft stick and provides additional cambial contact.
Making the inlay cuts on the stock while holding the graft stick firmly against it requires a little practice, as your thumb or fingertips cannot extend completely across the graft stick on the side that is being cut. To do so invites serious injury to your fingers and results in poorly made inlay cuts. The beginner should practice this maneuver a few times without the knife before attempting the inlay cuts.
|Beginning the right inlay cut.||Crossing over to make the left inlay cut.|
Place the surface of the long cut of the graft stick upright against the clean shield of live bark on the stock, with the slant cut positioned completely above the stock. Firmly hold the graft upright in place with the left thumb and begin the first inlay cut at the top of the stock on the right side of the graft stick. Draw the knife straight down the stock along the right edge of the graft stick to within half inch of the bottom of the graft stick, cutting completely through the bark and into the wood. It is very important to make this cut straight into the bark without angling the knife either to the left or the right.
|Making the left inlay cut.||Opening the inlay for graft insertion.|
Upon completion of the right inlay cut, do not allow the graft stick to move as you reposition your left hand to make the left inlay cut. You may have to hold the graft stick in place with your right hand as you reposition your left hand. Bring the left hand around the back of the stock to position just your fingertips on the graft stick. Then make the second inlay cut on the left side of the graft stick, cutting straight into the stock just as you did on the right side. If done correctly, the two parallel inlay cuts will be exactly the same width as the long cut section of the graft stick.
Open the bark flap between the two parallel inlay cuts and pull it slightly away from the stock. This may be facilitated by pricking it open with the point of your knife. Slide the graft stick between the bark flap and the wood of the stock. There should be no air space between the long cut of the graft stick and the flat surface of the stock. As you insert the graft stick, press the bark flap against it with your thumb to hold it firmly in place. Apply firm but gentle downward pressure to the top of the graft stick to force it into the inlay slot.
|Inlay graft properly positioned.||Opposite view showing the slant cut.|
Push the graft stick into the inlay slot until the bottom of the slant cut reaches the top of the stock. This exposed slant cut surface will form the callus and new tissue which will help cover the top of the stock and securely anchor the graft. Do not push the slant cut below the top of the stock because that will separate the graft stick from the flat wood, creating air space between the stock and scion. The top half of the bark flap can be cut off so a nail can be placed directly into the graft stick.
|Two nails hold the graft in place.||Aluminum foil in position.|
The graft can be secured by any one of several methods. Eighteen gauge 3/4-inch nails, 5/8-inch flat-point staples (inserted parallel with the graft stick), budding tape, floral tape and flagging tape have all been successfully used. Two of the 18-gauge nails have been used in this demonstration--one through the graft stick above the cut-off bark flap and one through both the lower part of the bark flap and the graft stick.
Tear a 12-inch square of aluminum foil from the middle of one side halfway down to the center of the square. While such precision is unnecessary, it may be helpful to fold the foil in half, then fold it in half again. Upon unfolding the foil, there are four separate folds from which you can choose to make this tear. Place the bottom of the tear vertically directly under the lowest bud, then fold the bottom half of the foil around the stock.
|Folding the upper parts of the foil.||Foil wrapping completed.|
Fold each side of the divided part of the square over the cut surface of the stock, being careful to cover all cut surfaces, including the slant cut of the graft stick. Crimp the foil to form a loose mold around the stock. Do not crimp the foil into the back side of the graft stick, i.e., the slant cut area.
|Bag in position over the graft.||Tying the bag to the scion.|
Cut off one corner of a pint or quart polyethylene bag. Slip the bag over the graft stick, with the graft stick protruding through the cut corner, and gently pull it down until the corner is positioned just below the lowest bud and above the slant cut. Tie the cut corner of the bag around the graft stick just below the lowest bud and above the slant cut so that no air leak occurs. Use a rubber band, small rubber strip or polyethylene tape so that the graft will not be girdled as it grows. Tie the lower end of the bag around the foil-covered part of the stock, i.e., the foil on the stock must extend below the bag. Make a small puncture above the lower tie to allow excess water to drain out of the bag. Then, coat the cut surface of the top end of the graft stick with household glue to prevent drying.
|Completed inlay bark graft.||Apply glue to the top of the scion.|
|Initial growth of the scion buds.||Note the callus formation on the cut stock.|
The buds on the graft stick should begin to grow in 4 to 6 weeks. Remove the polyethylene bag, foil and any tape when the new growth is over 6 inches long. Note the strong callus growth around the tree and graft stick. As the new shoots grow, keep them pruned back to 24 inches to prevent wind blowouts. If maximum growth of the graft is desired, select the strongest shoot at 6 to 10 weeks and tie it to a brace to prevent it from blowing out, removing the others. Otherwise, wait one year before selecting the strongest shoot on the graft. Tip prune all shoots which originate below the graft when they are 12 to 15 inches long. After 2 or 3 years when at least three-fourths of the cut surface of the stock is covered with new growth from the graft, remove all shoots that originate below the graft.
|Partially healed inlay graft.||Side view of partially healed inlay graft.|
|Scion shoot tied to a stake for support.||Wind damage to a young inlay graft.|
The graft is not totally safe until the entire wound area is healed over. Growth of the graft is likely to be strong and vigorous, so wind damage can result. In such cases, so long as there are buds above the graft, it can be pruned back to strong shoots.
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This procedure demonstrated by Larry A. Stein, Ph.D., the imagery and web posting by Julian W. Sauls, Ph.D.
This page was initially posted August 2, 2002