Does sap go up and down early in the season?

[Jim Foster]

Just wondered if when sap starts to run and you have an extended cold spell, does the sap that went up stay there or come down waiting for the next warm spell?

[DrTimPerkins]

On buckets/bags or gravity tubing, during a warm spell (a sap run), sap runs DOWN by gravity from an area extending from above the taphole to the top of the tree.

When the tree starts to freeze, water is pulled up from the soil through the roots and into the wood (stem and branches), where it then freezes.

During an extended freeze, the sap doesn't move...it is frozen.

On vacuum systems it is a little different, the main thing being that sap can be pulled a both down, sideways, and up in the stem. The zone the sap comes from is much larger.

[Jim Foster]

I see. The trees here must still be frozen pretty good as I have 25 taps out and not a drop from any of them. Daily temps have been around 30 to 45 and night time anywhere from 1 to 25 degrees. Was just wondering if you wait too long and the sap has been running, how much do you stand to lose from waiting....? The projected forecast here is cold through the end of Jan now.... And I have no one to turn to for advice around here because no one taps trees. Thanks, Jim

[berkshires]

I see. The trees here must still be frozen pretty good as I have 25 taps out and not a drop from any of them. Daily temps have been around 30 to 45 and night time anywhere from 1 to 25 degrees.

Yes, a tree is a big block of wood. The nights are still very long. You have about 9 1/2 hours of sun right now in Nebraska. After cooling that big block of wood down for 13 hours overnight, and the warmest part of the day is only a few degrees above freezing, your tree is not going to thaw at all before the sun goes down and it starts cooling down again.

This is part of why the sap runs better a little later in the season. Not only is it warmer during the day, it is warmer for *longer* and colder for *shorter*. So even for the same high and low temps over 24 hours, your tree will spend longer in the warm (daytime) temps, and shorter in the cold (night-time) temps, and so it will be able to thaw (and run).

You might get a bit of sap flow if it gets warm enough and you have plenty of sun, as the sun itself can warm the outermost layer of wood. Then again, if the ground is frozen really hard, the sap simply won't move much, because the base of the tree is just too frozen up for sap to be able to move back and forth between warm branches and warm roots.


Was just wondering if you wait too long and the sap has been running, how much do you stand to lose from waiting....? The projected forecast here is cold through the end of Jan now.... And I have no one to turn to for advice around here because no one taps trees. Thanks, Jim

Tap holes close over time, whether the sap is running or not. That's the risk in tapping too early: once the sap really starts running, if you've tapped too early the holes may already be starting to close, and you will not get as much or as long of a season as if you tapped later. I'm no expert, but I believe that as long as it's cold, the taps won't close very quickly, because the microbes that cause the tree to shut down are growing very slowly. Only later when it warms up do the taps start closing much faster.

Just cross your fingers and hope for good weather - that's all any of us can do!

Cheers,

Gabe

[Jim Foster]

Yes, a tree is a big block of wood. The nights are still very long. You have about 9 1/2 hours of sun right now in Nebraska. After cooling that big block of wood down for 13 hours overnight, and the warmest part of the day is only a few degrees above freezing, your tree is not going to thaw at all before the sun goes down and it starts cooling down again.

This is part of why the sap runs better a little later in the season. Not only is it warmer during the day, it is warmer for *longer* and colder for *shorter*. So even for the same high and low temps over 24 hours, your tree will spend longer in the warm (daytime) temps, and shorter in the cold (night-time) temps, and so it will be able to thaw (and run).

You might get a bit of sap flow if it gets warm enough and you have plenty of sun, as the sun itself can warm the outermost layer of wood. Then again, if the ground is frozen really hard, the sap simply won't move much, because the base of the tree is just too frozen up for sap to be able to move back and forth between warm branches and warm roots.



Tap holes close over time, whether the sap is running or not. That's the risk in tapping too early: once the sap really starts running, if you've tapped too early the holes may already be starting to close, and you will not get as much or as long of a season as if you tapped later. I'm no expert, but I believe that as long as it's cold, the taps won't close very quickly, because the microbes that cause the tree to shut down are growing very slowly. Only later when it warms up do the taps start closing much faster.

Just cross your fingers and hope for good weather - that's all any of us can do!

Cheers,

Gabe

Thanks for the reply. Hoping that by using spiles with hose that goes to a bucket that my early tapping won't dry out as fast as a spile with no hose, that allows more air to dry out the hose..

[DrTimPerkins]

Trees do not change temperatures are fast as the air does. They are quite well buffered. Always take a bit longer to thaw out at the beginning of the seasons. If you're getting air temperatures in the single digits, it would be unlikely that one warm day at 40 deg F would thaw them enough to run.

[MapleCamp]

You could put out some scout taps and when it gets going finish tapping. If your trees are big enough you can add taps when the early one slows down. I have tried check valve sprout on tube to bucket tapping very early with some success, others will say its a waste, but for me I say it helped. Just my 2 cents.

[blissville maples]

Dr. Tim- so the cold will induce an uptake of water thru the roots. Now during a warm spell as we had last week, and the trees are not tapped what happens to the sap in the tree? Does it build pressure in the roots and go back into the ground thru the same point it came in? Or does it stay in the tree and become sweeter and sweeter as time goes on?

[DrTimPerkins]

The transition from above freezing to below freezing creates a vacuum in the wood which induces water uptake. If the freeze happens too quickly, water uptake will be incomplete.

During a warm spell if the trees are not tapped, there will be a pressure within the stem of the tree (proportional to the height of the tree above the point in question). This pressure develops naturally as a way for the tree to refill wood vessels that have cavitated (filled with air) during the winter. Vessels (pipes) that are filled with air don't work very well to transmit sap -- kind of like getting air into your plumbing at home....it reduces their functionality. The pressure serves to dissolve the gas into the liquid and "repair" the pipe to full functionality. Different tree species get rid of the air in different ways...maples do it by stem pressure. The sap does NOT go back into the soil...there is a structure in the roots (the 'endodermis') which prevents this from happening. Some of the water in the branches may transpire (evaporate out) through the bark, but this is only a relatively minor amount.

[ddociam]

Thank you Dr. Tim. Here in southern Minnesota it’s to cold to do anything. All my Groves are filled with snow. I learned this year that the wise sapper gets his tubing in in the fall. I got my wire up and mainline installed just as the cold hit. Now I wait for reasonably warm days as I install lateral lines. The last five years I haven’t tapped until mid March. I have a lot of work to do.


Sent from my iPhone using Tapatalk

[billschi]

In addition to all the good information you've received there may be another tip. I'm not sure how much snow you have there but a good sign for me of when the trees are getting ready to run is when the snow melts away from the trunk of the tree. It tells me the tree is thawing out and getting ready to flow.

[GramaCindy]

In addition to all the good information you've received there may be another tip. I'm not sure how much snow you have there but a good sign for me of when the trees are getting ready to run is when the snow melts away from the trunk of the tree. It tells me the tree is thawing out and getting ready to flow.
I look for that same sign Bill.

[tgormley358]

The transition from above freezing to below freezing creates a vacuum in the wood which induces water uptake. If the freeze happens too quickly, water uptake will be incomplete.

During a warm spell if the trees are not tapped, there will be a pressure within the stem of the tree (proportional to the height of the tree above the point in question). This pressure develops naturally as a way for the tree to refill wood vessels that have cavitated (filled with air) during the winter. Vessels (pipes) that are filled with air don't work very well to transmit sap -- kind of like getting air into your plumbing at home....it reduces their functionality. The pressure serves to dissolve the gas into the liquid and "repair" the pipe to full functionality. Different tree species get rid of the air in different ways...maples do it by stem pressure. The sap does NOT go back into the soil...there is a structure in the roots (the 'endodermis') which prevents this from happening. Some of the water in the branches may transpire (evaporate out) through the bark, but this is only a relatively minor amount.

Hi Dr Tim,

I wondered if there are any ways to predict how long the trees will run sap during an extended warm
spell, like we have in central MA the last few days. It hasn’t been below freezing since Sunday I think, and sap still ran well in some trees yesterday. Today and tomorrow are still above freezing at night. Can trees keep running that long without a re freeze? I’m trying to forecast how much boiling I’ll be doing the rest of this week. Thank you.

[DrTimPerkins]

I wondered if there are any ways to predict how long the trees will run sap during an extended warm spell, like we have in central MA the last few days.

Not to any great degree. Keep in mind that trees are not simple pipes (although we sometimes use that analogy in explaining some things). Instead, they are collections of many thousands of individual pipes. In the early part of the season some of those pipes thaw out (those on the south side usually) well before the pipes on the north side thaw out. Under those conditions, sap can keep running (slow to weeping flows) from a tree for many days without a freeze/recharge happening. How long a tree will continue to run depends upon the size of the tree, the time of season, the weather conditions for a few days before the flow, the weather conditions during the flow, and whether or not you are on vacuum. With good enough vacuum, you can actually pull water from the soil, up through the roots, through the stem, and out of the taphole (which is how the "sapling" method works). The sap sugar content during this time will drop continuously until a freeze however....the difference is that without vacuum you'll likely get no sap (and thus no sugar) from those trees.

Short answer = no, not with any amount of certainty.

[Swingpure]

In addition to all the good information you've received there may be another tip. I'm not sure how much snow you have there but a good sign for me of when the trees are getting ready to run is when the snow melts away from the trunk of the tree. It tells me the tree is thawing out and getting ready to flow.

Attached are three photos, that my guess it would be time to tap. (I plan to use SapTapApp to help me decide when as well. The first is March 24, 2021, March 26, 2020 (I was still ice fishing then) and April 17, 2019.
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