Alaska Pioneer Fruit Growers Association

GRAFTING IN FEBRUARY ON POTTED ROOTSTOCKS

December 9, 1994

 

by Dwight Bradley

 

Old Method.—Like most growers in Alaska, I’ve usually done my apple grafting on bare rootstock in April. With whatever thawed soil I can rob from the greenhouse, I pot the new bare-rooted grafts as soon as I can, and stick them in a warm place to callous over and start growing. The pots give the trees a great headstart. If, alternatively, the bare-rooted trees are planted out in the ground as soon as they grafts have calloused over and the ground has thawed (mid-May or so), more than half of the grafts will fail, and those that do take will put on very slow growth.

 

Usually I’ll transplant the more vigorous grafts out in the orchard in June, once the graft has put on perhaps two feet of new growth. The slower-growing grafts get to spend their first winter in a heated garage, to give them an extra boost. I bring these trees inside just before the first frost and grow them at about 50°F under lights for another few months, until they finally notice that it’s time to shed their leaves. Then I turn the heat down to 35°-40° and try’ to keep them from reawakening until sometime around the first of May when it’s safe to pull them in the unheated greenhouse. The ultimate aim of all this, of course, is to get a better rate of survival in grafting, and to get trees into production sooner.

 

One interesting result of spending the winter indoors is that many one-year whips will bloom at the tip of the central leader. Whips that are going to tip-bloom usually show a pronounced thickening of the last inch or two of the stem. These blossoms should removed, of course, since the object of the first few years is to grow a tree, not a couple of apples. That is, if you can get other family members to admit that it really is better for the tree in the long run.

 

New Method.—In February, 1994, I was forced into an experiment that turned out to have even better results. I had turned up the temperature in the garage to around 60°F for a few days to paint our old truck. A few days later I was surprised to see about 20 potted Ranelka rootstocks starting to bud out. Most of these were either leftovers from the previous year’s grafting workshop, or survivors of earlier grafting attempts. Fearing that my 20 rootstocks were about to turn useless, I went around town for scionwood. Needless to say, what I got was still very dormant. Using a grafting machine, I made 20 whip-and-tongue grafts of about average quality. I stuck the pots in a 60°F room. Within a week, the first buds were poking through and within three weeks, all 20 grafts had sprouted new growth. (This is a much better batting average that I usually have. For comparison, at tire April grafting workshop, only about half of my bare-root grafts took.)

 

I turned on the grow lights in the garage, turned up the heat, and watched as the new grafts took off. When the weather finally warned up around the beginning of May, I moved the trees to the greenhouse, and stated giving them a few hours of direct sun whenever I could. Around May 25, I put them outdoors for good, first in partial shade under some brich trees and finally in full sun. With this coddling they hardened off pretty well, although the older leaves (the bottom six or eight) eventually got sunburned and looked as though they stopped photosynthesizing. In mid-June (a bit late, but this was the first chance I got), I planted the most vigorous trees in the orchard. One of these, a Geneva Early, was 7’ tail by summer’s end, and it had two or three lateral branches that were two feet long! Ginger Gold and Parkland did almost as well. For lack of space inside the existing orchard fence, I couldn’t plant out all of the trees, so about 5 of the weakest remained in pots all summer. A couple of those stragglers had reached 6’ by the time they came into the garage for the winter.

 

With the success of 1994 in mind, I had been planning on doing more grafting on potted rootstocks in March 1995. A few weeks ago (early January), however. I discovered most of my dozen or so Ranetka rootstocks were already starting to bud out. This meant that I had to do my grafting even earlier than last year. Interestingly, my Borowinka and Primifolia rootstocks are still fully dormant at this writing, Feb. 10. Ranetka seems to break dormancy at a lower temperature than the other two.

 

I would draw the following conclusions from what I’ve learned so far. (1) Grails on potted rootstock have a better chance of taking than grafts on dormant, bare rootstock. (2) Rootstock that is just breaking dormancy seems to work very well. (3) Grafting onto potted rootstock gives stronger first-year growth, presumably because the root system is already well established. (4) Given my setup (garage with grow lights, greenhouse, etc.), mid-March is probably about the optimum time for grafting. Much later and the trees won’t be well enough established to take full advantage of the long May days. Much earlier and the new trees will spend an awful lot of time under grow lights, and then may suffer sunburn when they are finally moved outside. I certainly wouldn’t recommend grafting in January! (5) The only disadvantage of which I’m aware are that it some additional care is needed (watering, turning on lights, moving trees in and out of the greenhouse, etc.), (6) One final advantage is that it gives a stir-crazy apple grower something to do during the long months indoors.