How much cold to recharge trees?

[TonyL]

Been a tough season thus far, which has me wondering: after a five day stretch of above freezing temps, how much time is needed, at 25 degrees, to recharge the trees and get sap flowing again? We had a couple decent runs earlier, but now we seem stuck in a weather pattern where we see 4-5 days and nights above freezing with daytime highs in the 50's and nighttime lows mid thirties, followed by one night where it falls to mid twenties for 5 hours or so, then back to the above freezing temps again for days. Sap flow is minimal.
I'm thinking the trees are essentially depleted of "flowable" sap, and a few hours of mid twenties just isn't enough?

If that's correct, how many hours are needed to bring sap back into the canopy?

[DrTimPerkins]

The wood tissue needs to freeze. Could be a partial freeze to yield a partial recharge. How long to freeze depends on several variables, but mostly on how warm the tree got, how cold the air gets afterwards, how long it stays below freezing, and how large the tree is (thermal mass).

[maple flats]

I've found 27F or lower yields best, but higher can still give you a run, especially if you have vacuum.

[TonyL]

Have you ever noticed the timing involved, Dave? That's what I'm wondering about, and what I think Dr. Perkins is alluding to. Temperature is only part of the equation, with time spent at that lower temp also playing a big role. If it gets down to 27 degrees for only an hour or two before starting to rise again, then how much benefit is gained?

As sugarmakers we often tell people that "it needs to get above 40 degrees during the day, and mid twenties at night" to trigger a run.... but that's not exactly the whole story. By telling folks that, we're really only providing a partial, and partially correct, answer.

[DaveB]

As sugarmakers we often tell people that "it needs to get above 40 degrees during the day, and mid twenties at night" to trigger a run.... but that's not exactly the whole story. By telling folks that, we're really only providing a partial, and partially correct, answer.

It's really complex though. I usually describe it as the freeze/thaw cycle that triggers the capillary action in the tree. Obviously briefly reaching 27 won't allow the outer portion of the tree to fully freeze so you don't get full effect but if it's been 27 for several hours, it might. Freezing of the wood is the key.

A bigger and related question is how long can it stay warm and shut the trees down? This week is really mild here and it's been mild but next week and beyond look seasonable with a pattern change. I know a lot also depends on sunlight and thankfully while the next few days are very warm (50s and 60s) it will be cloudy. I'm hoping they hold since it's still early.

[HowsItRunning]

Here are a couple examples from last year [1-tap gravity]

In the first plot you can see day 2 of the flow [Mar 18] is much less than the previous day without a good freeze. After several days with no hard freeze there's a decent flow, then a hard freeze really helps:
plot_1t (1).jpg

In this plot you can see flow drop off over days without cold temps, even though the temperature keeps increasing every day:
plot_1t (2).jpg

[Openwater]

Now that is some very useful information regarding the timing of sap flow and being able to see it overlayed on temperature over time. It appears that among all the factors affecting sap flow, temperature clearly has the biggest influence.
It would be nice to see the same information plotted over an entire sugaring season and then compare year to year.

[berkshires]

Here are a couple examples from last year [1-tap gravity]

In the first plot you can see day 2 of the flow [Mar 18] is much less than the previous day without a good freeze. After several days with no hard freeze there's a decent flow, then a hard freeze really helps:
Attachment 22882

In this plot you can see flow drop off over days without cold temps, even though the temperature keeps increasing every day:
Attachment 22883

That is amazing data. Thanks for sharing! I would certainly be interested to see more about what happens after a freeze. I'll check out your link.

Dr Tim, you might not have the kind of detailed (drops per second) data, but do you ever share any hard data along these lines? Most of what I've seen from y'all is best practices and general discussions of the factors involved.

GO

[TheNamelessPoet]

Now that is some very useful information regarding the timing of sap flow and being able to see it overlayed on temperature over time. It appears that among all the factors affecting sap flow, temperature clearly has the biggest influence.
It would be nice to see the same information plotted over an entire sugaring season and then compare year to year.

There is always the saptapapps.com. I just started using ut this year, and honestly... I REALLY like it. I feel like its kind of a lot of work for each run (just based on the data you want to keep) but man to see over the next couple years could end up invaluable!

[HowsItRunning]

Here's data for the entire 2022 season, it may be difficult to see. Last year was the first year for the website and i didn't tap-in until Feb 22. This year I tapped-in the site on Feb 14. The hope is to get data from Feb 15 to Apr 15 every year, hoping the taps don't dry up toward the end, it seemed fine last year.

Solar radiation also seems to influence the flow, which may seem obvious. Some have mentioned pressure might influence the flow, I have the data but haven't looked into it. I know pressure effects the quality of the boil, at least with wood anyway.

https://howsitrunning.com/uploads/plot_season_1t.jpg