By BOB PURVIS
Bench-grafting stone fruits in the spring can be done, but the requirements for success are more rigorous than are those for apples or pears. In late January I discussed with Dr. Brian Smith, the stone-fruit breeder at the University of Wisconsin at River Falls, what the requirements are for bench-grafting cherries. Based on his experience, he said that cherry rootstocks should not be grafted when totally dormant, but when there is about ¼ to ½” of new growth coming out of the top of the rootstock. Possibly because the buds and leaves of cherry are large and use a lot of water, he recommends keeping freshly grafted cherry rootstocks at a temperature of 55 to 60F in a high-humidity environment. At those temperatures, callus tissue will form but the scion buds will be slower to break dormancy.
By contrast, bench grafts of apricot should be kept at about 65 to 70F, but like cherry they need to be kept in a high-humidity environment. Plum grafts seem to callus OK at the same temperature as apricots. I have never bench-grafted peaches successfully in the spring, possibly because they have an even higher heat requirement to form callus tissue. (Also, dormant peach wood is punky or splintery and hard to cut easily with a knife.) The best after-care for cherry, apricot, or plum grafts I can recommend is to put them in a 3 to 5 gallon plastic pot, or a 5-gallon plastic bucket with drainage holes, with the roots covered up with moist potting soil or possibly sawdust and maintained as moist. To maintain high humidity, I pull a large plastic laundry bag over the top of the bucket, being careful to prevent direct contact of the plastic (which will soon become wet) with the tops of the scions on the grafts. I tie the mouth of the bag loosely with heavy twine. After some of the grafts begin to take, gradually loosen the mouth of the bag to let in drier air, so the leaves on the scions can get used to it. Do not allow the plastic bag to contact the newly forming leaves on the scions, or they will rot; but do keep the pot or bucket in bright indirect light after the leaves begin to emerge, so that they will become green and better able to endure direct sun a month or so later.
Take good care of the roots on the rootstocks: do not let them get too wet, nor too dry. When you transplant your successful grafts into pots or possibly a nursery area outdoors, you should see a fair number of new, white hair roots protruding from the rootstock.
I would welcome comments on this article from other members of the APFG, sharing their experiences and lessons learned with grafting stone fruits. (Of course, most of us know that commercial nurseries almost always propagate stone fruits by T- or chip budding in August. Another NAFEX member here in Minnesota tells me, however, that Van Well Nursery in Wenatchee, WA has gone to bench-grafting sweet cherries on Gisela dwarfing rootstocks in the spring, because they seem to have much better success doing so as opposed to August budding.