[NAFEX] Spring grafting
david.maxwell at dal.ca
david.maxwell at dal.ca
Wed Apr 7 19:04:42 EDT 2010
I have been field grafting my apple trees for 30 years (dormant scion grafted to actively
growing rootstock), but realised this year that I really have never thought it through fully. I
have always taken "bud break" of the rootstock as the time to do my grafting. But this year
we (and it appears, a lot of other places) have had a dramatically early Spring, and weeks of
temperatures in the high teens and low 20's Celsius - this translates to 65-72 degrees F.
This has caused buds to swell considerably, many now being at green tip. But we are now
predicted to have temperatures for the next week (or more), back down to some 5 or 6
degrees C (40 F), and I suspect that grafts placed now would never callus in. Any advice on
when would be a good time to graft?
And, a supplementary, (and far more problematic) question. I have gotten scion wood from
several sources, who have been experiencing similar conditions. This has resulted in their
cutting the scions after their trees had likewise started to break dormancy. Now the "gospel"
is that the scion must be dormant to graft successfully. But 1) I am not sure I have ever seen
any actual evidence of this - has anybody got any personal experience to contribute? and 2)
more "scientifically", what is the mechanism here? Is it a question of changes in the cell
walls of the cambium cells (which thicken in the Fall, as dormancy sets in, and then start to
multiply - with thin walls - as growth resumes) or is it rather a simple question of metabolic
demands in the scion which has started to grow (ie. broken dormancy), in particular a
question of water movement? In the first instance, there is nothing we can do to modify
events. But in the second instance, doing things to prevent the scion from dessicating before
it gets vascular channels established with the rootstock may be all we need to do to get a
good take despite the scion having broken dormancy. Anybody got any experience to offer?
And, just to gild this lily a bit more, I note on one batch of scions, in which the terminal buds
were left in situ, that it is the terminal buds which have broken dormancy, while the buds
farther proximal on the stem are not obviously swollen. If I use these more proximal buds for
grafting, am I likely to get a better take? (I suspect that what is happening here is that the
terminal bud is sending inhibitory chemicals back down, and keeping the buds below from
sprouting - a non-temperature-related dormancy process.)
And, finally, might I do better, with my non-dormant scions to chip bud them, rather than graft
(whip and tongue), on the principle that the metabolic demands would be much less?
David Maxwell, officially zone 5b Maritime Canadian. (But more like Florida at present)
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