What is the perfect temp for a wintering storage shelter?

abqjoe

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So I will be building my wintering shelter this coming week and it will be on the north side of my yard tucked away within two cinder block walls and my house itself. I will be framing out the walls using 2x4's and insulating the stud cavities with blue Dow board to keep temps consistent. That being said, I will also be using a programmable thermostat outlet which I will be plugging a small space heather into and I am wondering what you guys think is the best temp to set it at without having to mulch. I am thinking 35F which would allow the temp to drop to 29-30F before triggering the thermostat. The shelter will be 12' long, 4.5' wide, 8' tall in the front angling down to 7' in the rear to allow water to fall off into a catch.

I'm sure most everyone here knows what tree's I have because I've posted several pics but here is a list of the tree's that will be in there anyway:)

4 Japanese Maples
2 Elms
1 Hackberry
1 Ume/Plum
2 Junipers
1 JBP
1 Boxwood
1 Ponderosa

JBP, Junipers, and Ponderosa won't go in there until temps drop into the teens.
 

JudyB

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I keep mine (in a perfect world) between 25 and 40 air temps. (I'd like to keep it around 35, but on warm days without a chiller it's hard) I have heat mats, and have two different sides with two different temps for hardier and less hardy trees. I keep these just above freezing and around 40 for the less hardy trees. Had this setup for years, and my trees come out banging in the spring. You may want to invest in some lights, so you don't have to two step when they wake up. I've been happy that I did that.
 

coh

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I keep most of my trees in a plastic enclosed shelter in my barn, with a good thermostat and an electric space heater. I aim to keep the temp at or above about 27-28 F, though it has gone lower at times. So far, that has worked very well for a mixed collection of trees. Everything you listed would most likely do fine. I did have some damage two winters ago (the really long/cold winter) - no outright losses, but I had the apex die back on a trident and most of the finer branches died back on a sweetgum. Not sure why, maybe the heater was on too much and it got too dry.

Note, my approach was based on what Bill V does, which seems to work pretty well...
 

Stan Kengai

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Ideally, I would aim for a constant temperature just above or just below freezing. The two biggest things to avoid are too low temps and the freeze thaw cycle. Freezing and thawing every day, like we often get here, is very hard on the root systems, soil and sometimes pots. Thankfully, my garage keeps plants above freezing all winter.
 

miker

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This is a subject I am certainly following closely since this my first year wintering trees in the north, versus Florida in past years. As such, I have at least several non-tropical trees that "wintered" fine in the Orlando area in the past without being in the refrigerator to add supplemental chill hours. These are: Pinus clausa, Torreya taxifolia, Acer floridanum, Acer rubrum(Fl stock), Juniperus "Procumbens nana" and though it is my first year, I am guessing Acer buergerianum formosanum would fit in this category too. That is, temperate trees that can/ and have survived and done well in a climate with few if any net chill hours. They clearly need a somewhat pronounced cool down, but not a real winter at all (Orlando).

My thought is to leave them outside through November here in PA, then put them inside with my two tropicals for the remainder of the winter. I wonder how this will work?

I may put the Southern sugar maple, red maple and Taiwan trident in the garage instead.
 

rockm

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good luck with that...Really think an insulated enclosure with a heater is overkill for what you have. None of the species you've listed would need all that protection in Zone 7a or 7b, which I think you're in. Overprotection is just as bad as underprotection.
 

Vance Wood

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It always depends on where you live and what you grow as you are now finding out. Depending on what you grow the necessity of a "shelter" of the free standing variety are un-necessary for the most part. I know when you start out doing bonsai every thing you want to do and every purchase you want to make becomes bonsai related but where you live preparing for the coming Ice Age is probably unlikely. You just need to keep the trees where they are sheltered from direct sun and direct, extended and continuous winds. If you have critter problems then it's a whole new ball game, a permanent shelter may be necessary. However I knew someone who built an in-ground shelter for his trees and did not check it out properly. Basically he created a winter habitat for a bunch of rabbits and a pretty nice food source. So---no matter what you do or where you go there you are.
 

abqjoe

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It always depends on where you live and what you grow as you are now finding out. Depending on what you grow the necessity of a "shelter" of the free standing variety are un-necessary for the most part. I know when you start out doing bonsai every thing you want to do and every purchase you want to make becomes bonsai related but where you live preparing for the coming Ice Age is probably unlikely. You just need to keep the trees where they are sheltered from direct sun and direct, extended and continuous winds. If you have critter problems then it's a whole new ball game, a permanent shelter may be necessary. However I knew someone who built an in-ground shelter for his trees and did not check it out properly. Basically he created a winter habitat for a bunch of rabbits and a pretty nice food source. So---no matter what you do or where you go there you are.

True, we don't get Arctic temps out here but we do regularly go into the low single digits and occasionally into the negatives. I'm trying to figure a close to perfect temp without having to mulch because I don't want to attract mice and I'd probably use straw to mulch with otherwise.
 

rockm

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The solution to not getting mice is not to shelter your trees in a heated, insulated structure. That is the perfect environment for mice in the winter. That's what they're looking for and why they come into houses/garages/etc. in the fall.

Mulch isn't the problem. Oversheltered areas combined mulch (or not) are the problem with mice. If trees are left mulched in a sheltered area of the yard, mice still have to contend with predators and are less likely to attack your trees. Inside, they don't face that challenge and are free to eat at their leisure because you've provided them with a nice, safe, warm place.

If you're concerned about rabbits, put a chicken wire fence around the mulched trees outside. A lot cheaper and more effective than the structure you're planning.

I am in the same grow zone as you. I mulch everything (including Bald cypress, elms, trident and Japanese maples, barberry, and more than a few others) into the ground or in an open cold pit--November through March.

I don't provide any protection for my ponderosa or amur maples. I leave them out on the benches all winter. Both can handle it. Done it for years.
 

aml1014

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I like my structure because it provides me a working area throughout the year, and when winter comes I lug them in and when spring comes I lug them out, more simple that way for me. I don't worry to much about temp fluctuations as I have plenty of experience with coldframes thanks to my work and I know the sweet spots.

Aaron
 

Vance Wood

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Here is what I do. I do not put my trees into their winter quarters, where ever that might be, until after the first hard frost. This prompts the critters to find their shelter and not find your trees as a sheltering spot. Of course that does not protect you against the immigrant critter force but it definitely discourages the residents. I have used lean-to's, I have used bales of stray and the combination of the two. I have found that finding a sheltered area where you can put as many trees as possible with a fence or wall on one side where the most sensitive of your trees are placed. Then; I place the more hardy trees in front of the more sensitive and if necessary I cover them with straw and perhaps make a straw wall in from of the whole mess. It ain't pretty but it works. If you are going to use the straw method realize that Spring clean up is a mess and do not apply the straw until latter after everything has been put away. I have said it before the cold wind (freeze drying) and the sun (early dormancy break) are you two biggest enemies. If you are worried about rodents you can scatter moth balls around your trees that will discourage the hairy little bastard.

Here again; it all depends on the material you are growing.
 

rockm

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Here is what I do. I do not put my trees into their winter quarters, where ever that might be, until after the first hard frost. This prompts the critters to find their shelter and not find your trees as a sheltering spot. Of course that does not protect you against the immigrant critter force but it definitely discourages the residents. I have used lean-to's, I have used bales of stray and the combination of the two. I have found that finding a sheltered area where you can put as many trees as possible with a fence or wall on one side where the most sensitive of your trees are placed. Then; I place the more hardy trees in front of the more sensitive and if necessary I cover them with straw and perhaps make a straw wall in from of the whole mess. It ain't pretty but it works. If you are going to use the straw method realize that Spring clean up is a mess and do not apply the straw until latter after everything has been put away. I have said it before the cold wind (freeze drying) and the sun (early dormancy break) are you two biggest enemies. If you are worried about rodents you can scatter moth balls around your trees that will discourage the hairy little bastard.

Here again; it all depends on the material you are growing.
I do pretty much the same thing. All my trees are left out through at least November. They get hit with repeated frosts and then freezes, then heavier freezes, but because it's November, freezes usually don't last more than a night or two. Although November before last (if I remember right) we had teens for the last week or more of the month. I brought some trees into the basement for that period, because of the prolonged cold. Once temps evened out, I put them all back outside under mulch.

You set up will probably also force early bud break in a lot of your trees. Good luck with that.
 

abqjoe

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Just for the record, I'm not trying to keep my winter structure warm by any means! What I'm trying to do is find the happy temp that would allow me to store my tree's away for the winter without mulching and without worrying about the roots freezing. The area where I'm building this structure is permanently shaded and doesn't receive sun ever during any time of year. The Dow blue board for insulation is only to keep the desired temp within the structure consistent. I will not even be building a floor in there, figured why build a floor if I have to water once a week/2 weeks. It will be sitting on top of gravel.... So I guess the simple question would be: At what temp do the roots freeze at?
 

Vance Wood

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Just for the record, I'm not trying to keep my winter structure warm by any means! What I'm trying to do is find the happy temp that would allow me to store my tree's away for the winter without mulching and without worrying about the roots freezing. The area where I'm building this structure is permanently shaded and doesn't receive sun ever during any time of year. The Dow blue board for insulation is only to keep the desired temp within the structure consistent. I will not even be building a floor in there, figured why build a floor if I have to water once a week/2 weeks. It will be sitting on top of gravel.... So I guess the simple question would be: At what temp do the roots freeze at?
There's another misinformation. With the exception of some deciduous/sensitive trees, freezing the roots is not a bad thing. It seems that bonsai people that live in areas with less severe winters are under the misconception that you must not allow the roots to freeze on trees,---- any trees. This simply is not true. My trees freeze solid every winter. The problem is keeping them in the dormant condition and not allowing them to awaken early. That's what kills your trees. Your biggest enemy starts in February where the temperatures may rise enough to stimulate early growth than along comes March and the sub-zero stuff. The water in the newly risen sap will expand and split the cambium and in many cases the trunk with it and the tree may die.
 

aml1014

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Just for the record, I'm not trying to keep my winter structure warm by any means! What I'm trying to do is find the happy temp that would allow me to store my tree's away for the winter without mulching and without worrying about the roots freezing. The area where I'm building this structure is permanently shaded and doesn't receive sun ever during any time of year. The Dow blue board for insulation is only to keep the desired temp within the structure consistent. I will not even be building a floor in there, figured why build a floor if I have to water once a week/2 weeks. It will be sitting on top of gravel.... So I guess the simple question would be: At what temp do the roots freeze at?
It depends on the size of container, and how much moisture is in the pot. Larger containers that are watered well won't freeze solid very fast, where as your little shohin trident would freeze very quickly. It depends as usual.

Aaron
 

Vance Wood

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It depends on the size of container, and how much moisture is in the pot. Larger containers that are watered well won't freeze solid very fast, where as your little shohin trident would freeze very quickly. It depends as usual.

Aaron
Tridents are a problem. If I had a Trident Shohin I would remove it from the container and place it in a box where I could pack the soil ball with Pine Bark mulch. I would then put it back in the same pot in the spring. I have seen Tridents stay out without shelter unpotted and they did fine. I have seen Tridents left in pots where the roots turned to snot by spring. It seem the physical contact with a pot has a deleterious effect on the roots when frozen.
 

abqjoe

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Tridents are a problem. If I had a Trident Shohin I would remove it from the container and place it in a box where I could pack the soil ball with Pine Bark mulch. I would then put it back in the same pot in the spring. I have seen Tridents stay out without shelter unpotted and they did fine. I have seen Tridents left in pots where the roots turned to snot by spring. It seem the physical contact with a pot has a deleterious effect on the roots when frozen.

Mine is a Trident root over rock Shohin. So what you're saying is that I'd be better off pulling it from the pot and transferring it over to a larger container and pack it in Pine Bark?
 

rockm

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Just for the record, I'm not trying to keep my winter structure warm by any means! What I'm trying to do is find the happy temp that would allow me to store my tree's away for the winter without mulching and without worrying about the roots freezing. The area where I'm building this structure is permanently shaded and doesn't receive sun ever during any time of year. The Dow blue board for insulation is only to keep the desired temp within the structure consistent. I will not even be building a floor in there, figured why build a floor if I have to water once a week/2 weeks. It will be sitting on top of gravel.... So I guess the simple question would be: At what temp do the roots freeze at?

Yeah, you kiiiinda are trying to keep the location nice and cozy warm, comparatively.

Like most beginners, you're thinking (consciously or unconsciously) that your plants need to be coddled with an "optimum" temperature. None really exist, save between 25 and 40 degrees. That's the range you ideally want to keep to, but there is substantial leeway with species.

I live in the same growing zone as you. What you're describing is overkill for just about every species you've got. The only candidates that this might benefit from such a sheltered location are your shohin sized maples. They are the most susceptible to temperature swings, even in mulch, since their pots are too shallow to benefit from a deep mulch covering (although they are more easily protected by snowfall).

Frozen roots ARE NOT A PROBLEM. They are kind of what you're looking for within reason of course.

What is a danger is frozen intracellular water. There is a big difference between frozen roots and icy intracellular water--it is part of the bedrock of understanding how to overwinter bonsai.

By and large (and this varies tremendously) this is how it works, first the water in the soil freezes around the roots, then the roots freeze, then the water inside the roots' individual cells freeze. This doesn't happen all at once and it varies species to species.

This explains it well
https://www.evergreengardenworks.com/frzekill.htm

BTW, I've had tridents in Zone 7 for decades. No issues if they are under eight inches of mulch in a well drained location. Mine have withstood more than a few winters that saw single digits and below.
 

rockm

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It depends on the size of container, and how much moisture is in the pot. Larger containers that are watered well won't freeze solid very fast, where as your little shohin trident would freeze very quickly. It depends as usual.

Aaron

No. It does NOT really depend on the size of container. It's not that simple. It mostly depends on what's IN the container.

The soil in a 6 inch pot can freeze solid with no problems, just as the soil in a 24" pot can too. It all depends on the species in the pot's ability to withstand Intracellular freezes. Those kinds of low temperature come with extreme, constant lows below 15 degrees or so (this is tremendously variable). Smaller pots can reach those lows more quickly because they have smaller mass, but those same temperatures can affect larger containers as well.

A Ponderosa pine in a solidly frozen six inch pot at 0 F will be fine for days, while a Japanese maple at that temp in a 12" container will get winter kill or lose branching...
 
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