Day Night Temp Differential When Coming out of Dormancy

Next week here in Zone 5b New York daytime temps are forecast to hit 60. Night-time temps will barely break freezing if at all.

So my question is …
When or if should I start to worry about too early dormancy break? or…
What combination of day-night temps and the duration of each triggers the wake-up alarm?

Last frost date here is late April early May.

Mike

Yeah interesting question. Very unlucky. here during that time highs will be in the 40’s and low is still below freezing at night, so I’m good. And I’m in 6a, so much for zone ratings.

I think the baseline temperature that stimulates growth for most stone fruit is pretty low. Probably not much above freezing. I base that on the fact that scion wood and seeds in the fridge both seem to start growing at temp in the 30s. If that applies to trees after chilling it’s a simple growing degree hour relationship. Every hour above say 35F stimulates growth. Growth rate is proportional to degree hours above 35F. One hr at 45F is 10 degree hours. One hr at 65F is 30 degree hours. Sum those up day and night after chilling is satisfied and at some total for each cultivar you reach blooming.

@fruitnut

So… do I understand it correctly that…

After chill requirements are satisfied over winter and tree is dormant, it now takes a certain amount of “warming” hours for the tree to wake up? . If so, this is a different set of “hours”. Is there a database where the “warm up hours” info is available?

Not that it will help much to know since there is not much we can do about it but maybe I can avoid some worry and at the same time I can save a hair or two on my follicle challenged scalp.

Mike

Yes you understand correctly. I don’t know of any tables of heat requirement.

In apples heat can make up for lack of chilling. So high chill apples that don’t get adequate chilling, say in southern CA, will still bloom after a long period of heat. That even happens here. Some of my apples bloom from May until July.

Certain species bloom late despite very low chill requirement. That’s because their heat requirement is very high. This would include things like grape, figs, pecan, Asian persimmon, and some mulberries.

I’ve notice that some peach/nectarine seeds will sprout in the fridge and some will not sprout until taken out of the fridge.