Bark Grafting, Step by Step
By Tim Smith, WSU Extension Professor Emeritus
At times, when growers wish to quickly change the variety of trees growing on “difficult” soils, grafting is a reasonable alternative to replanting.
Before you start, be certain that the rootstock and trunk will provide a good understock for your future orchard, the grafting stock and the parent trees are free of injurious viruses, fire blight bacteria*, and that you have addressed the possible propagation rights of the variety.
Fireblight bacteria can be present, but symptomless, in bud wood and grafting wood. You should take great care that the mother tree used for propagation material has not had blight strikes the season that the wood is gathered, even if the strike was removed soon after it appeared. Mark the blighted tree and let one winter pass before you take any wood.
There are several ways to graft trees, the “bark graft” shown below is perhaps the most popular and successful method used in North Central Washington.
In late winter, cut the trees back to within about 1-2 feet (30-60 cm) of where you wish to place the grafts. Some grafters believe that leaving a “nurse limb” (a modest size scaffold low in the tree) will help the grafted tree through its first grafted season. Others skip this step.
Keep the grafting wood cool and humid after you gather it in late winter, while it is nearing the end of dormancy.
A few minutes before you carry out the grafting, cut the graft site to the final length, so that the stub will have a fresh live end.
Using a straight-edged knife, cut through the bark to the wood. Make the incision about 2-2.5 inches (5-6 cm) long, and parallel to the direction of the limb being grafted.
Select approximately “pencil” sized scion wood. Make a smooth, flat cut slanting across the lower end of the wood, leaving an exposed area about 1 1/2 inches (40 mm) long.
Warning: this is the most difficult step to do correctly, and the most important. Practice makes near-perfect. If your knife is sharp enough to do this job right, be careful that you do not slice a hunk off of your hand during this process.
“To guarantee a good flat surface on the scion stock, hold a small sharp block plane, Stanley Tools has one that fits nicely into the palm of your hand, with the cutting surface up and facing away from you. Holding the scion stock in the other hand in an exaggerated pencil grip with the butt end facing away from you, draw across the knife of the plane two or three times.
Start the cut in back of the lowest bud on the stock you want to save. Apply a little pressure on the butt end of the stock to get the desired angle. We typically then rotate the wood and make one stroke on the opposite side to achieve a chisel point. Very seldom do I have to waste a bud because the knife of the plane whittled away too much wood. For someone who is handy with a knife carrying two tools is maybe redundant. But for someone like me who is not handy this is very fast. Using bark grafting we get very good take. In a very short time you learn the different pressures you need to apply for differences in the scion wood.”
Contributor of the above:
Moose Hill Orchards
Insert grafting wood into the layer where bark and wood separate. This is the layer where there is active wood and bark growth, and your objective is to place the wood-bark interface of the scion wood firmly, for its entire length, against the wood of the grafted tree, so meristem growth can connect the two.
Gently tap the scion wood into the bark incision, line up the top of the cut area of the scion wood with the cut edge of the tree. Then carefully shave away some of the rough bark projecting out from the incision area.
Nail the scion wood to the tree trunk with a small “brad”. Gently, now.
This nail will serve to firmly hold the scion wood meristem tissue to the tree limb meristem. This firm contact is critical.
After the scion wood has been placed about every 4 inches (10 cm) along the circumference of the limb, wrap the entire end of the cut limb with plastic flagging tape.
Coat the end of the cut limb with heavy wax or tar based wound dressing to prevent drying and the early introduction of wood rots. This may take two or three coats applied starting as soon as the scion wood placement is completed, and continuing over the next day or two. Paint is not an acceptable substitute.
Beware of potential fire blight infection in flowers that may emerge late from the scion wood. If fire blight weather occurs the first season, remove the flowers (gently). Scissors are more gentle than pulling.
Most grafters strongly recommend that the young, growing grafts should be supported with string
attached to wood bracing attached to the limb during the first season of growth. Otherwise, there is
danger that windstorms will break out the graft before it has the opportunity to gain structural strength.
The below pictures are of the grafted tree the next Spring.
And below is a picture of the grafted tree in Spring of year 2:
During the first three or four seasons after grafting, the rapidly growing grafts may face micro-nutrient mineral deficiencies. In Washington, the most common problems are Boron and Zinc deficiency. It seems the trees grow so vigorously that they outstrip the ability of the tree to deliver these nutrients at the higher than normal levels needed by a mature or newly planted tree. Take care to supply these nutrients through foliar application. Light rates are sufficient, but applications need to be more frequent than necessary under normal orchard growing conditions.
Four years later (M7 rootstock)………………