Calculating the best tapping date

[DaveB]

With things being so wonky this year and being a scientist (meteorologist/IT guy by trade) I wanted to try and bring some "science" to the "art" of tapping and seeing if there is a formula for when to tap trees based on past data and current weather patterns. I've been at this for over 30 years and an old sugar maker that I learned most of what I know from told me when I was starting out to just tap around the same date each year and not pay too close attention to the weather forecast. I knew that I was mostly done by the end of March so I backed that up 6 weeks and have been tapping around 2/14 every year like clockwork.

This has mostly worked out but years like this I think I'm missing some early runs and since I know have access to vacuum systems, check valve spouts and long term forecasts that I never dreamed of 35 years ago I thought I should take advantage of that. I also have 40 years of weather records on my farm so I know what the weather has been like for the past 40 maple seasons and would like to see if there was a way to calculate when the best tapping date would have been based on the weather.

I did some searching and I saw one post about calculating degree days to determine that but it doesn't look that that is a valid method. I also found an article by the good Dr Tim about using the average temperature in a long term forecast to determine the tapping date but no determination on what temperature is best.

I know there are other factors to tapping such as wind, rain/snow and barometric readings but in the end I think it comes down to when the trees start budding. That was clear to me this year and we had a prolonged period of extremely warm weather, including the warmest January I've ever had. We returned to "normal" winter weather and on days when the sap should have been flowing extremely well, I just wasn't seeing good flows. It almost seemed like the trees were thinking it was late March when it was still the end of February. Knowing that, is there a way to calculate how many degrees days it takes before the trees start responding like that? I'd like to look at past years and see if I could have spotted that.

[maple flats]

My method has mostly been to look at the 2 week forecast, and when that shows a few sap flow days I tap. I say mostly because about 8 yrs ago I had 3 college age workers as my only help, at that time I started fixing lines on Jan 2, and my goal was to be tapped by Jan 20-21, because my help had to be back at school then.
If you are on vacuum tubing it works fine being tapped ahead, if on buckets that won't work.

[littleTapper]

Well, this is my best year ever and I tapped on February 4th. So, that's clearly the best day to tap. Sample size of 1, all that's needed, right? Totally scientific!



That out of the way, there may be ways to get predictions that are close, but jeez, things are so different year to year. I tend to look at long-range forecasts and then with how things have been going, gauge when to tap.

The data wrangler in me, since that's a part of my day job, would like to have free time to start crunching on some numbers. But, too busy making syrup!

[Sugar Bear]

With things being so wonky this year and being a scientist (meteorologist/IT guy by trade) I wanted to try and bring some "science" to the "art" of tapping and seeing if there is a formula for when to tap trees based on past data and current weather patterns. I've been at this for over 30 years and an old sugar maker that I learned most of what I know from told me when I was starting out to just tap around the same date each year and not pay too close attention to the weather forecast. I knew that I was mostly done by the end of March so I backed that up 6 weeks and have been tapping around 2/14 every year like clockwork.

This has mostly worked out but years like this I think I'm missing some early runs and since I know have access to vacuum systems, check valve spouts and long term forecasts that I never dreamed of 35 years ago I thought I should take advantage of that. I also have 40 years of weather records on my farm so I know what the weather has been like for the past 40 maple seasons and would like to see if there was a way to calculate when the best tapping date would have been based on the weather.

I did some searching and I saw one post about calculating degree days to determine that but it doesn't look that that is a valid method. I also found an article by the good Dr Tim about using the average temperature in a long term forecast to determine the tapping date but no determination on what temperature is best.

I know there are other factors to tapping such as wind, rain/snow and barometric readings but in the end I think it comes down to when the trees start budding. That was clear to me this year and we had a prolonged period of extremely warm weather, including the warmest January I've ever had. We returned to "normal" winter weather and on days when the sap should have been flowing extremely well, I just wasn't seeing good flows. It almost seemed like the trees were thinking it was late March when it was still the end of February. Knowing that, is there a way to calculate how many degrees days it takes before the trees start responding like that? I'd like to look at past years and see if I could have spotted that.

I too pick 2/15 as my projected tap date. I pick this date because I don't want the first two weeks of March to pass me by without my taps being more than four weeks old. It is my belief that the first two weeks of March at my long lat produce the most sap and best syrup of any two weeks of the year. By Far. So I tap not to miss them with reasonably fresh taps.

This year I backed my start date up 9 days and taped on 2/6. The weather was just too darn CRAZY to wait to the 15th.

With that said, my best sap flow was in the second week of March this year where I was getting 16 inches of natural on 5/16th tubing and had back-to-back 100-gallon days of sap flow somewhere around the 8th and 9th of March. I set my record with at least 800 gallons of sap this year. I pulled my taps yesterday after a final small run of 40 gallons of sap. The season is over in these parts.

I am going to stick with my 2/15 start date and 3/1 through 3/14 "be ready" theory until the sun completely melts the polar caps.

And will accept the fact that I am not going to catch every run unless I have separate bushes to tap at different times of the year.

And will take note and file neatly into the back of my extremely forgetful brain, the fact that an extremely warm January is as much of a reason not to tap as it is to tap.

I do know of another sugar maker in CT who also happened to tap on Feb 6th and had his second-best season in his many years.

Giving in to January is kind of like giving up on March, and that is a mistake in sugaring across this belt of the range. That is well written in the evolutionary scripts of these trees.

That is of course my opinion and my conjecture and easily wrong in any one particular season but easily correct over time and multiple seasons.

[Swingpure]

I experimented with tapping at different times this Spring. In our area normal tapping time might be around mid March. Although I tapped some trees in December, I tapped more in mid February and the balance at the beginning of March. My February gamble may have paid off more if the polar vortex had not been disrupted.

That being said, the lesson I learned is that trees in February (for our area) do not flow the same as they would in late March or April. The hours of sunlight is much less and the duration of time that the temperature stays at a daily peak temperature is less. So in February the temperature might reach 41°/5° but only for a short while.

This might be the wrong term, but what I am referring to is the potential for a tree to flow. Given the same parameters of snow, etc, a tree tapped later in the tapping season has a greater potential for flow.

Of note, the trees I tapped on lines in December are still flowing, and just with the eye test looking at what is coming out of the lines in comparison to lines that were tapped later, they have at least equal flow.

Knowing what I know now, barring exceptionally warm Spring, I will wait for when the potential for flow is greater and I will wait until at least March 7 before I tap.

A caveat is that 2 hours south of us in Southern Ontario they had warmer temperatures and basically no snow and they tapped earlier than normal, with great results. The lack of snow was a factor in their early success, so there are many variables, which makes coming up with a calculation or formulae, to tell you when you should tap, very complex.

[DrTimPerkins]

There are a number of factors that influence when sap will flow. A degree-day calculator is probably not going to be enough to be terribly reliable unless you have a really good forecast of the upcoming weather from the selected tapping date to the projected flow date. Sap flow (especially early in the season) is not just dictated by temperature, but also by prior temperature (if it's been really cold it takes a while for the trees to thaw), sun (to help thaw), precipitation type and duration, wind, etc. Forecasts of temperature are reasonably good....but terrible for these other things.

The BEST time to tap for highest yield would be the day before it started to flow. However, given that it takes some time to get everything ready and tightened up (if on tubing), then people have to tap earlier. The amount of time varies depending upon how many people you have helping, how many trees, the terrain, the weather, and especially the depth of snow.

Any projection would rely tremendously on the forecast and/or would assume that the weather is going to remain on the same trend. I think we saw this year that it did in some areas, but definitely did NOT in others. Huge variation.

Producers also need to keep in mind their collection method (gravity or vacuum) and sanitation level to understand how long their tapholes will remain viable (and how well they will flow during that period).

Don't get me wrong...I like math...I like projections...I can clearly see where would be an interest in this. I just doubt it would be any more useful than choosing a date based upon historical averages and modifying slightly (ahead or back) based upon the conditions (snow, help, prevailing temps, etc.).

[DaveB]

I started going back through my weather & sugaring data and the best correlation I could find as a predictor of when the trees started slowing down their sap production was when the 15 day average temperature went above freezing. This year was tough because it never went below freezing in January but I've had other mild years like 2012 & 2002 where I was basically done by mid-March so tapping in January would have given me my optimum 8 week window.

Speaking of finding the optimum 8 week window, I've been going back through the data and finding the last date where the 15-day average temp was above freezing and going 6 weeks back from there. It looks like I have about two weeks after that date where the sap will run for a total of 8 weeks.

I've gone back so far to 2002 and the average date for when the trees started to slow down on sap production was mid-March. That correlates with being done at the end of March. I may move my tapping date up a week or two because I rarely collect sap in April and that would give me 8 weeks instead of the current 6 week window I'm giving myself.

For years like this year when the average temp is above freezing in January I may just have to tap in January but I need to look at the data better.

I'll share more data but wanted to share that observation from my data.

[DaveB]

There are a number of factors that influence when sap will flow. A degree-day calculator is probably not going to be enough to be terribly reliable unless you have a really good forecast of the upcoming weather from the selected tapping date to the projected flow date. Sap flow (especially early in the season) is not just dictated by temperature, but also by prior temperature (if it's been really cold it takes a while for the trees to thaw), sun (to help thaw), precipitation type and duration, wind, etc. Forecasts of temperature are reasonably good....but terrible for these other things.

The BEST time to tap for highest yield would be the day before it started to flow. However, given that it takes some time to get everything ready and tightened up (if on tubing), then people have to tap earlier. The amount of time varies depending upon how many people you have helping, how many trees, the terrain, the weather, and especially the depth of snow.

Any projection would rely tremendously on the forecast and/or would assume that the weather is going to remain on the same trend. I think we saw this year that it did in some areas, but definitely did NOT in others. Huge variation.

Producers also need to keep in mind their collection method (gravity or vacuum) and sanitation level to understand how long their tapholes will remain viable (and how well they will flow during that period).

Don't get me wrong...I like math...I like projections...I can clearly see where would be an interest in this. I just doubt it would be any more useful than choosing a date based upon historical averages and modifying slightly (ahead or back) based upon the conditions (snow, help, prevailing temps, etc.).

Appreciate the response Dr Tim. I know it's a nuanced process and that the best seasons (for me) follow what you've mentioned. What's interesting to me was looking at the drop-off of my collected sap was when my 15-day average temp went above freezing, at least for the past 20 years. On average that happens in mid-March for me and I'm usually done collecting by the end of March or two weeks after that date. In years where that date occurred earlier or not at all, I was usually done 2-3 weeks after that as well. Of course that just marks the end of the season and not when to tap but at least it gives me an average date and I can look at the extended weather forecast tools that are available and see if it makes sense to tap prior to that date or after.

Does Proctor make sap collection data available or at least dates of your last sap collected or boil? I see your weather data is available and I'd be curious if the same correlation I'm seeing works for your site as well.

[Sugar Bear]

I experimented with tapping at different times this Spring. In our area normal tapping time might be around mid March. Although I tapped some trees in December, I tapped more in mid February and the balance at the beginning of March. My February gamble may have paid off more if the polar vortex had not been disrupted.

That being said, the lesson I learned is that trees in February (for our area) do not flow the same as they would in late March or April. The hours of sunlight is much less and the duration of time that the temperature stays at a daily peak temperature is less. So in February the temperature might reach 41°/5° but only for a short while.

This might be the wrong term, but what I am referring to is the potential for a tree to flow. Given the same parameters of snow, etc, a tree tapped later in the tapping season has a greater potential for flow.

Of note, the trees I tapped on lines in December are still flowing, and just with the eye test looking at what is coming out of the lines in comparison to lines that were tapped later, they have at least equal flow.

Knowing what I know now, barring exceptionally warm Spring, I will wait for when the potential for flow is greater, and I will wait until at least March 7 before I tap.

A caveat is that 2 hours south of us in Southern Ontario they had warmer temperatures and basically no snow and they tapped earlier than normal, with great results. The lack of snow was a factor in their early success, so there are many variables, which makes coming up with a calculation or formulae, to tell you when you should tap, very complex.

Great commentary by all on this thread. With regards to the Rookie above, he already knows a lot more about this then I do and already makes a lot more syrup than I do. Must be the Canadian blood and the symbol on his national flag.

To bolster the Rookies point above, I will add that many years ago I read a cool article in the Wall Street Journal of all places ( a great newspaper at the time ) Not sure about today. The article was about what makes deer shed antlers. There was significant proof that deer shed antlers based on the amount of daylight hours in a day and that weather ( warm, cold, snowy, rainy) had little to do with it. The point of the article being that the angle of the sun at a given latitude was the most determining factor in when deer shed antlers, and by far.

Now I am not saying the same thing is true with Maple Trees.

But I believe it is a HUGE factor in when Maple Trees determine when their Triple Witching Hours of sap flow will be. The trees can react to a rising sun in the sky day to day VS a sinking sun in the sky day today. I.E. spring VS fall.

Late November and early December ALWAYS have great freeze thaw cycles, but we almost never consider tapping then. Even though some sap will flow then, we know better, and the trees know better too. But yes, they do flow sap when convenient opportunity arises.

But I try not to let that S me in, even in January regardless of the weather.

If the earth shifts on its axis to any measurable degree, I might change my plan accordingly.

[DrTimPerkins]

That being said, the lesson I learned is that trees in February (for our area) do not flow the same as they would in late March or April.

I think that lesson had been learned a long time ago by a great number of maple producers. As I recall, several folks here provided you with some advice on that subject several months ago.

It's difficult for producers sometimes to hold off when they get the itch that spring is coming and the weather seems good for a day or two. It typically takes more than that for good flows to happen. It is even more difficult when you hear about others out there tapping and even making syrup. Keep in mind that these early folks usually fall under a couple of different scenarios:
1. They only tap some of their trees early and tap the rest later.
2. They are in southerly locations and/or have normally warmer sugarbushes.
3. They are LARGE producers with tens of thousands of taps, so they have to start early to finish by the time the good sap flows start. They KNOW that some of their taps will be dry early, but a portion of them won't (given the difference in the time they were tapped). They also tend to be folks who have high vacuum and really good taphole/spout sanitation.

This might be the wrong term, but what I am referring to is the potential for a tree to flow. Given the same parameters of snow, etc, a tree tapped later in the tapping season has a greater potential for flow.

No, this is absolutely NOT correct. Sap will flow from trees whenever the conditions are correct. Sap flows will happen any time when there are freeze-thaw conditions. It is a nearly purely physical phenomenon. Said more precisely, if the conditions for sap flow are met, sap will flow irregardless of the time of year. In fact, we can place branches in the freezer any time of year and upon removing them, sap will exude from the ends. The trees don't have a calendar for when sap flows. They do however have a physiological time for various sap sugar content. This has only a marginal effect on sap flow.

That given, there is a much higher potential for the tree to thaw more quickly in March or April. That has nothing to do with the tree. It is due to solar influences (longer days, more sun) and the fact that the prevailing temperatures are such that the trees are closer to the freezing point and not deeply frozen (in which case they take a long time to thaw out). It has almost nothing to do with the "potential" for the sap to flow. The tree doesn't dictate the flow potential...the environmental conditions (mostly wood temperature...not air temperature) do.

The other influence regarding tapping time is taphole viability. This is related to sanitation and microbial growth in the taphole. Once drilled, the process of compartmentalization starts. We just don't see it because it happens inside the tree. Life functions happen (albeit slowly) even at really cold temperatures. Compartmentalization is slow when it is really cold, and picks up when it is warm (as does microbial growth in the taphole...the thing that elicits taphole compartmentalization and reduced sap flow rates). Tapholes that are open (on gravity) or tapholes where the equipment (spouts/droplines) are not well sanitized will "clog" faster than tapholes that are on vacuum (constantly pulling any sap AWAY from the taphole) and tapholes in which the equipment is new or well sanitized (or with CV spouts). This process happens fairly quickly for gravity collection....you can expect a taphole to remain viable AND produce well for only 4-8 wks (depending largely on wood temperature, with sap flow slowing down considerably near the end). On good, consistent vacuum with good sanitation, we can extend the taphole viability and high sap production rates up to 12+ weeks.

All of this is quite well understood. Not at all certain why we have to "learn" it again and again.