How far will a freeze get us?

[Starting Small]

Last week was too cold for any flow, this week the days are perfect but the temps are just about freezing overnight. I was wondering if we got a night at around 25 degrees and the days were warm, like the 40's if this could sustain a flow for 1 day, 2 days, more without an additional freeze? Thanks!
-Dave

[happy thoughts]

In my own short experience multiple day flows had more to do with stormy weather and low pressure especially when night temps hovered just barely above or below freezing.

[smokeyamber]

If its running it may keep running even if it doesn't get cold at night. I has some run last year when it was 80deg... and not getting below 32 at night...

Key is if the trees are done for the season... i.e. budding

[Tweegs]

If I remember right, on those longer runs the sugar content will start falling off.
Trade off, more sap, but less sugar.

[happy thoughts]

If I remember right, on those longer runs the sugar content will start falling off.
Trade off, more sap, but less sugar.

I think you're right tweegs. I also remember reading something about longer runs being a mixed blessing.

[bemer]

Rember your science. The ice crystal forming in the twig has to pull the sugar into it as the free molocules gather and form a new grouping. Then when the twig thaws the sugar is transported, in solution, to storage. This is where we come in. The changes in pressure only influence water flow. The flow starts when the twig thaws. The best runs come in the fog. The second best run comes in the rain. The sugar content is determined by the available sugar in the twig. This is determined by the overall vigor of the tree. Trees in slight distress should have the highest sugar content. Trees with wet feet have small storage nodes and therefore make less sugar. This last observation comes from the many trees uprooted in the storms that I have taped in the past.

[DrTimPerkins]

....if we got a night at around 25 degrees and the days were warm, like the 40's if this could sustain a flow for 1 day, 2 days, more without an additional freeze?

You end up with a "weeping flow" as a result of gas bubble expansion in the wood fibers. Won't last indefinitely, and flow rates will drop off.

[Ed R]

My dad had an adage that he quoted occasionally that I've found to hold pretty true on buckets or gravity. It will run GOOD for exactly the the same amount of time it froze the the night/days previous to the run until it freezes again.

[markct]

Usualy my lines on vac will run 2 or 3 days without a freeze but after the first day gravity lines slow way down. The vac runs often produce huge quanities of sap when this happens as they are running around the clock when there isnt a freeze

[DrTimPerkins]

Usualy my lines on vac will run 2 or 3 days without a freeze but after the first day gravity lines slow way down. The vac runs often produce huge quanities of sap when this happens as they are running around the clock when there isnt a freeze

Lines on vacuum (especially high vacuum) can run almost indefinitely, although the flow will slow down somewhat (and eventually plateau) and the sugar content will slowly drop off. In essence, when a tree first thaws out, there is a positive pressure phase (sap running out due to high sap/stem pressure in the tree). After the pressure is fully dissipated (flow due to gravity potential and gas bubble expansion), the trees will eventually enter a negative pressure phase (if on vacuum -- if not on vacuum, flow will slow down greatly and then will stop within a few days). When in the negative pressure phase, water will be pulled from the soil up through the roots, into the stem (where it mixes with sugars), and out through the taphole. This will continue as long as it doesn't freeze and the vacuum pump stays on. So in the first part of a run, most sap runs down and out of the taphole, but in an extended thaw, if you have vacuum, the sap eventually runs up. This wasn't well understood until about 4 yrs ago when we were doing experiments looking at how sap was moving within trees. We're still filling in the gaps in the details.