Overwintering with a mini-greenhouse?

Bonsai Noodles

Yamadori
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I read a few threads on how greenhouses are a bad idea for overwintering trees — especially temperate ones. But would it work for me though, since I live in Zone 4a (Minnesota). That means winters can dip as low as -20/-30 F, and average winter temperature high/lows are 30-10 F. If the greenhouse raises temperatures only 20-30 degrees F, then that might actually be optimal for a Japanese Maple with cold hardiness as low as 5 (which would mean you'd need a 7 zone for potted trees). So the 20-30 degree bump would theoretically work? Or do I not understand greenhouse mechanics correctly?

Interested to hear your guys' thoughts on this...

Here's a picture of one I'm buying anyway for other purposes in my garden.

Edit:
Dimensions of the greenhouse are roughly 11 feet diameter and 7 feet height.

Also, just to note, I'm already planning on putting trees in my insulated/nonheated garage over the winter. Maybe I'll do an experiment and risk a tree to see if the greenhouse method would work...
 

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LittleDingus

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I read a few threads on how greenhouses are a bad idea for overwintering trees — especially temperate ones. But would it work for me though, since I live in Zone 4a (Minnesota). That means winters can dip as low as -20/-30 F, and average winter temperature high/lows are 30-10 F. If the greenhouse raises temperatures only 20-30 degrees F, then that might actually be optimal for a Japanese Maple with cold hardiness as low as 5 (which would mean you'd need a 7 zone for potted trees). So the 20-30 degree bump would theoretically work? Or do I not understand greenhouse mechanics correctly?

Interested to hear your guys' thoughts on this...

Here's a picture of one I'm buying anyway for other purposes in my garden.

Edit:
Dimensions of the greenhouse are roughly 11 feet diameter and 7 feet height.

Also, just to note, I'm already planning on putting trees in my insulated/nonheated garage over the winter. Maybe I'll do an experiment and risk a tree to see if the greenhouse method would work...

Is that rated to withstand the bluster of a Minnesota winter? Do you not get high winds in winter?? Or is that a myth ;)

Also, greenhouses only trap heat when there is heat to trap. They might climb 20 degrees on bright sunny days (but maybe not? The sun it pretty low up in them parts). They might not climb at all on overcast days. And I suspect they fall quite a bit at night.

I'm not an expert on greenhouses by any means. Just applying the physics I know to how I think they work. Don't let me discourage you but you might be wary if you fdont have satisfactory answers to my niave questions ;)
 

Bonsai Noodles

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Is that rated to withstand the bluster of a Minnesota winter? Do you not get high winds in winter?? Or is that a myth ;)

Also, greenhouses only trap heat when there is heat to trap. They might climb 20 degrees on bright sunny days (but maybe not? The sun it pretty low up in them parts). They might not climb at all on overcast days. And I suspect they fall quite a bit at night.

I'm not an expert on greenhouses by any means. Just applying the physics I know to how I think they work. Don't let me discourage you but you might be wary if you fdont have satisfactory answers to my niave questions ;)

Very good questions. I did look up the manufacturer's guidelines, and they say it can withstand up to 40 MPH winds. I've not paid attention as much to wind speeds until now, but I do see that winds only ever go as high as around 30 MPH in the part of MN I'm from. Now, how it will stand against cold+wind, I'm not too sure, to be honest. I'll think about this!
 

penumbra

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I think there are too many variables for this to be successful for a new greenhouse person. What has been said is true of heat trapping. It can be really detrimental when it traps too much heat without ventilation. I don't know your neck of the woods but you can generally expect pretty drastic temperature fluctuations. I particularly think Japanese maples are a bad idea unless you can monitor temperature changes very well. I can just see those maple waking up in February.
Another thing already expressed, when I look at the greenhouse you are buying the word Cute comes to mind. It is certainly not a serious greenhouse at all. The plastic is only one layer so there is no insulation. And the poles are really thin. The shape would add some strength, but you better plan on putting it in a protected area and staking it down. If it says good to 40 MPH, I wouldn't trust it at 30 MPH.
Wish I could tell you more about locating it, but your climate is much more severe than mine.
Best of luck.
 

MrWunderful

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Pretty sure the “best” temp to keep a j. maple at during dormancy is around 30°F but I may be wrong. Other maples I know can survive lower, japanese too but that far outside the range they can be finicky.
Will this green house get you close to 15-30° F?
 

penumbra

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Pretty sure the “best” temp to keep a j. maple at during dormancy is around 30°F but I may be wrong. Other maples I know can survive lower, japanese too but that far outside the range they can be finicky.
Will this green house get you close to 15-30° F?
You are pretty darn close regarding temps for Japanese Maples. They will take colder but not over long periods.
Yes, it is for certain that the greenhouse will get close to 30 F. The problem is that it will absolutely not hold it there. In my area, zone 6, a greenhouse like this if not vented could reach 100 F on a sunny winter day. And depending on the physical mass inside the greenhouse and using no passive heat retention system, it would drop down to about 4 degrees warmer than the outside on a long winter's night. That is really cold in zone 4.
 

Bonsai Noodles

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I think there are too many variables for this to be successful for a new greenhouse person. What has been said is true of heat trapping. It can be really detrimental when it traps too much heat without ventilation. I don't know your neck of the woods but you can generally expect pretty drastic temperature fluctuations. I particularly think Japanese maples are a bad idea unless you can monitor temperature changes very well. I can just see those maple waking up in February.
Another thing already expressed, when I look at the greenhouse you are buying the word Cute comes to mind. It is certainly not a serious greenhouse at all. The plastic is only one layer so there is no insulation. And the poles are really thin. The shape would add some strength, but you better plan on putting it in a protected area and staking it down. If it says good to 40 MPH, I wouldn't trust it at 30 MPH.
Wish I could tell you more about locating it, but your climate is much more severe than mine.
Best of luck.

Hmm, as you suggest, the stability is going to be the potential issue here. I’d say I’m more worried of that since I’m planning to keep one of my landscape trees under this dome. It’s staked, and others have said they hold up okay in winter. But Minnesota is especially harsh.

Pretty sure the “best” temp to keep a j. maple at during dormancy is around 30°F but I may be wrong. Other maples I know can survive lower, japanese too but that far outside the range they can be finicky.
Will this green house get you close to 15-30° F?

I’ll have to see! I think if anything, I might put the maples under the greenhouse come spring and keep them in the garage for the rest of the time. In Minnesota, the weather can be finicky even up to April (we get snow in April sometimes even). So perhaps for the purpose of my potted bonsai, they shouldn’t stay there over the winter. But perhaps, a landscape tree already planted in the ground can use the extra heat.
 

LittleDingus

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Hmm, as you suggest, the stability is going to be the potential issue here. I’d say I’m more worried of that since I’m planning to keep one of my landscape trees under this dome. It’s staked, and others have said they hold up okay in winter. But Minnesota is especially harsh.



I’ll have to see! I think if anything, I might put the maples under the greenhouse come spring and keep them in the garage for the rest of the time. In Minnesota, the weather can be finicky even up to April (we get snow in April sometimes even). So perhaps for the purpose of my potted bonsai, they shouldn’t stay there over the winter. But perhaps, a landscape tree already planted in the ground can use the extra heat.

How many trees are we talking here? What kind of footprint do they take up? Are they all maples?
 

Bonsai Noodles

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Bad idea. If it is growing there don't attempt to change its growing conditions. It's going to get cooked and then its going to freeze.

Oh wow, really? It's in a place that's somewhat shaded by tree leaves — would that still be bad? I made the bad mistake of planting a very sentimental Zone 5 tree in my backyard (an apricot tree), and I'm finding ways to make sure it can survive this winter now. It's not been there in the past. I was planning to mulch, wrap in burlap, etc., but I just keep feeling paranoid now about it. I don't pamper my other trees nearly as much, but this one's a particularly important one.

Edit: There are also vents in the greenhouse, so maybe that would help?
 
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Bonsai Noodles

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How many trees are we talking here? What kind of footprint do they take up? Are they all maples?

A 1-year-old apricot tree grown from seed. One really. I'm finding ways to make sure this one survives, and the maples going under the greenhouse was just an afterthought in all honesty.
 

MrWunderful

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I obviously cannot speak to MN winters (thank you 65° for most of year Bay area) but generally landscape trees will survive where potted trees wont because Because of the constant temperature of the ground. So you may be ok without needing to protect it, but I would consult someone who is familiar with gardening and the area.
 

Bonsai Noodles

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Another strategy for this apricot tree is to dig it back up and then put it into a pot... What do you guys think...? I'm just scared all the transplanting would be bad this late into the season.

I obviously cannot speak to MN winters (thank you 65° for most of year Bay area) but generally landscape trees will survive where potted trees wont because Because of the constant temperature of the ground. So you may be ok without needing to protect it, but I would consult someone who is familiar with gardening and the area.

Great point. I'll definitely contact someone local to see...
 
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MrWunderful

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Another strategy for this apricot tree is to dig it back up and then put it into a pot... What do you guys think...? I'm just scared all the transplanting would be bad this late into the season.

I definitely would not mess with roots at all at this point.
 

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Try a solid windbreak out of plywood or something without enclosing.
 

LittleDingus

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A 1-year-old apricot tree grown from seed. One really. I'm finding ways to make sure this one survives, and the maples going under the greenhouse was just an afterthought in all honesty.

I certainly understand sentimentality! I have several trees I'm overly attached to myself.

This may not be the best forum for the information you're looking for. You might look for a forum on fruiting trees or general gardening. That may turn up a better skill set for the goals you're trying to accomplish.

Take the rest of this at your own risk. It is what I would do but my experience and motivations differ from yours...

The baby apricot I'd winter indoors. I'd let it stay outside until it went dormant. Even then, I'd leave it outside as ling as temps are safe. If you can monitor the temps in your garage, I'd put it there on the ground near an interior wall if you can. Leave it there as long as it is safe. Bring it inside to a cool closet or basement once the garage is no longer safe. Keep the soil damp...not wet. Don't be surprised if you need to water...it will evaporate in your winters. But water sparingly. Once inside, if it starts to sprout...let it grow. The brightest window you can. Get a cheap spot grow light just for it if you can (I have one that I grow orchids under). Keep it on the cool side if you can.

The ourside apricot I would wrap the trunk with tree wrap. There are commercial products available. You want to protect as much of the trunk from drying wind as you can. The bark is going to want to crack and peel in the cold dry winds. Tree wrap can help protect against that. If you can put up a wind break to keep the worst of the wind off, that may help too. Mulch deep and several feet out from the trunk if you can. Mound the mulch so its like a volcano around the trunk. You want to keep excess moisture off the bark near the base but you want to hold ground heat around the roots. Tree wrap down as low as you can wrap should help the trunk.

Again, with limited thought and only empathic concern for the consequences having been in a similar situation, that's what I would do. Don't follow any of this advice if you have any concerns about it what so ever. I don't want the guilt of having killed your mother's favorite tree :(
 

Bonsai Noodles

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I certainly understand sentimentality! I have several trees I'm overly attached to myself.

This may not be the best forum for the information you're looking for. You might look for a forum on fruiting trees or general gardening. That may turn up a better skill set for the goals you're trying to accomplish.

Take the rest of this at your own risk. It is what I would do but my experience and motivations differ from yours...

The baby apricot I'd winter indoors. I'd let it stay outside until it went dormant. Even then, I'd leave it outside as ling as temps are safe. If you can monitor the temps in your garage, I'd put it there on the ground near an interior wall if you can. Leave it there as long as it is safe. Bring it inside to a cool closet or basement once the garage is no longer safe. Keep the soil damp...not wet. Don't be surprised if you need to water...it will evaporate in your winters. But water sparingly. Once inside, if it starts to sprout...let it grow. The brightest window you can. Get a cheap spot grow light just for it if you can (I have one that I grow orchids under). Keep it on the cool side if you can.

The ourside apricot I would wrap the trunk with tree wrap. There are commercial products available. You want to protect as much of the trunk from drying wind as you can. The bark is going to want to crack and peel in the cold dry winds. Tree wrap can help protect against that. If you can put up a wind break to keep the worst of the wind off, that may help too. Mulch deep and several feet out from the trunk if you can. Mound the mulch so its like a volcano around the trunk. You want to keep excess moisture off the bark near the base but you want to hold ground heat around the roots. Tree wrap down as low as you can wrap should help the trunk.

Again, with limited thought and only empathic concern for the consequences having been in a similar situation, that's what I would do. Don't follow any of this advice if you have any concerns about it what so ever. I don't want the guilt of having killed your mother's favorite tree :(

Really appreciate the advice and empathy in this situation! I think your advice is what I’ve been hearing on other forums. Only thing new I might do is set up some form of a windbreak. Maybe enough layers of the winter cloth and a garbage bag can achieve that though. Or not. We’ll see..
 

LittleDingus

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Gotcha. I think the best strategy now is to try my best at insulating the tree with things like burlap and bubble wrap. Next season, hopefully if it survives the winter, I can try to move things around...

Don't use bubble wrap! It will trap moisture and cause rot.

You're insulating the roots for warmth. A deep mulch out several feet from the trunk...maybe out past the dripline is your best bet for keeping the roots "warm". Don't mound the mulch against the trunk though...volcano it.

The trunk you're mostly insulating from desiccating winds. Not much you can really do about the temperature. Burlap is fine but I think some of the engineered tree wraps may be better. You want something that breathes so it doesn't trap moisture but prevents the bitter air from leaching moisture from the trunk itself. If you're just trying to get through this winter, I'd wrap it pretty tight to help support the bark. It's the drying out of that cambium layer that's going to cause most of the problems. If the bark starts to split, that layer can dry out right fast.

From a freeze/thaw standpoint, water is unique in that it actually increases in volume when first transitioning to a solid. That's why ice floats. It's less dense as a solid than as a liquid. This is true til about 4 degrees below freezing. Then ice starts to shrink in volume with decreasing temperatures again. Those first few degrees just under freezing are where the damage to cell tissue is the worst. Unless you want to get extremely drastic and wrap the trunk in heat tape. It is very likely to go through that freezing zone.
 

LittleDingus

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Really appreciate the advice and empathy in this situation! I think your advice is what I’ve been hearing on other forums. Only thing new I might do is set up some form of a windbreak. Maybe enough layers of the winter cloth and a garbage bag can achieve that though. Or not. We’ll see..

No solid plastic around the trunk. It's counter intuitive but you want to insulate against (slow down) the movement of moisture, not prevent it entirely.
 

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