Overwintering - Guidance

dbonsaiw

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First winter with my trees and kind of confused how to proceed with winter. I have some trees in an unheated garage. It is detached and air gets in all over. The pots will freeze in there if cold enough. I have the rest of my trees in a "greenhouse" in the backyard. It's more of a tent than a greenhouse and only protects from wind and rain. It will raise the temp during the day slightly but not at all at night. It does however raise the humidity significantly. There is a cold front coming in tonight and temps will drop into the teens.

My question is should I just bring all the trees into the garage where I get the same wind protection and much lower humidity, leave things as is or add some additional protection to the trees in the tent? I was thinking about wrapping the boxes in bubble wrap, creating a little fence around and above the box and filling that fence with some mulch. Thoughts?
 

Dav4

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I think you're over protecting your trees. On the ground with some mulch covering most of the pots, out of the winter sun and wind is about all you need, assuming the trees are cold hardy. I'm in 6 a with tridents, palmatums, black pines and other species mulched and frozen solid on my patio... temps hit 3 F the other morning and won't be above freezing for more then an hour or two for the foreseeable future.
 

dbonsaiw

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I think you're over protecting your trees. On the ground with some mulch covering most of the pots, out of the winter sun and wind is about all you need, assuming the trees are cold hardy. I'm in 6 a with tridents, palmatums, black pines and other species mulched and frozen solid on my patio... temps hit 3 F the other morning and won't be above freezing for more then an hour or two for the foreseeable future.
Those few sentences are more calming than Xanax.
 

dbonsaiw

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I guess I'm thoroughly confused about overwintering Japanese maples in pots. It's in the low teens today and feels like 1 degree with wind chill. Everything is obviously frozen solid. The tent these guys are in does nothing to increase the temperature, especially at night. During the day I can get it up a few degrees, but leave the doors unzipped so this doesn't happen. I wrapped some of the boxes, including the tridents, in some bubble wrap. The tent basically protects from wind and rain/snow. So I guess my question is when should I ever be worried? It shouldn't get much colder than it is today this winter. If there's a blizzard I can close the tent or move the trees. Otherwise, I think I'm hearing to just relax, water when needed and wait for spring?
 

Dav4

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I guess I'm thoroughly confused about overwintering Japanese maples in pots. It's in the low teens today and feels like 1 degree with wind chill. Everything is obviously frozen solid. The tent these guys are in does nothing to increase the temperature, especially at night. During the day I can get it up a few degrees, but leave the doors unzipped so this doesn't happen. I wrapped some of the boxes, including the tridents, in some bubble wrap. The tent basically protects from wind and rain/snow. So I guess my question is when should I ever be worried? It shouldn't get much colder than it is today this winter. If there's a blizzard I can close the tent or move the trees. Otherwise, I think I'm hearing to just relax, water when needed and wait for spring?
When I lived in Massachusetts, I kept many of my trees on the cement slab floor of an unattached garage, all mulched with wood chips and left to freeze solid for the winter. One year, I decided to get a cheap indoor outdoor thermometer with a 6 foot long wire and probe to provide the outdoor reading while the actual thermometer sat on top of the mulch and provided the indoor reading. I placed that probe on the cement slab before placing a potted tree on top of it and winterizing my trees there. That winter, even though the trees experience temperatures inside the garage in the single digits, the temperature that the outdoor probe encountered never fell below 32°F. Again, the mulch and soil in the pots was frozen before Christmas and it did not thaw out until late March… Temperatures at the soil level didn’t fall much below freezing if at all. If your trees are winter hardy as landscape plants, the ambient air temperature in the low teens or single digits won’t be an issue if they are protected from the wind while being frozen. It’s all about the temperature at the root zone, and that’s why mulching is important.
 
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Vance Wood

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The most important thing is to get them dormant and keep them there as long as possible, even frozen till March. It is the freeze thaw freeze cycles that kill trees. Shovel snow on them this does more than you can imagine to help them.
 

dbonsaiw

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Apologies in advance for all the noob questions. I wrapped some of my trees in bubble wrap and can fill the space with some pine shavings. I guess I shouldn't be watering too much over the next few months, but how does one water once the tree is completely mulched? Just water the mulch?
 

Deep Sea Diver

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At this point I can’t tell for sure where your trees are, but I’ll take the liberty of thinking these are stored outside now in your ‘tent’…. and that your collection doesn’t include Azaleas.

I’ve used greenhouse ‘cold frames’ for a number of years. You are correct, thesewill not protect much from extended freezing spells, but will provide shelter from the wind to avoid desiccation. These also keep the soil about 1 F warmer then a plant out of the cold frame during winter weather based upon my daily temperature observations.

The downside is these enclosures also keep the air still inside… promoting fungal growth during warming transition times. So keep leaving the flaps open during days predicted above 39F and closed when below these temps …. and wide open when it rains enough to wet the soil inside… will help.

The reason why folks tend to mulch, bury pots into the soil or, even better, both is to moderate temperature changes both advice and below freezing. Also the moisture in the spit tends to help keep the mulch moist and the media in the pots moist…to a point… that’s why you open the cold frame during rain..

I bury and mulch the non greenhouse trees inside cold frames. This provides the very best protection from breaking dormancy during warm spells and damage to the roots of the plants (which are the most frost sensitive part of the tree). Some people say it’s overkill around here, yet they also complain about winter damage when there isn’t any here.

Bubble wrapping the pots complicates the situation and may impede drainage. My recommendation is to remove the bubble wrap, get a couple bags of medium bark nuggets. Shake the bags to get the fines to the bottom of the bag, decant the nuggets and wet the bark down. Then pack the bark around and atop the pots.

After that all you s will have to do is monitor the cold frame.

After wintering over this year you will have a much clearer idea of what to expect.

….. and… That’s all folks!

Good Luck
DSD sends
 

dbonsaiw

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Thanks. I do have one azalea in the tent that I collected from my front yard.

The bubble wrap is only around the boxes, not the bottoms. Does that change the analysis? I don't see how this could impair drainage.
 

Deep Sea Diver

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Hmmm…. Can you please post us multiple images of your setup and which species of trees you possess? That will give everyone a clear picture of your situation.

You mentioned Japanese maples to begin then tridents …. and now an azalea. What else are you dealing with….?

That will help cut down on the back and forth nature of this thread

Cheers
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dbonsaiw

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Attached is a pic that shows the setup. Azalea on the front right, tridents in the round pots and the other 3 are Japanese maples waiting for their trunk chops.
 

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rockm

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Thanks. I do have one azalea in the tent that I collected from my front yard.

The bubble wrap is only around the boxes, not the bottoms. Does that change the analysis? I don't see how this could impair drainage.
Bubble wrap is useless. It does nothing to help. Bubble wrap isn't made for insulation. It's made to protect against impact. Bubble wrapping them then leaving the root masses exposed to surrounding air is useless. You can't conserve heat that isn't there. The soil and wrap will just freeze together.

You have to protect the root masses from exposure on all sides of the container to be successful in protecting them/

You have the wrong idea about overwintering. As Vance W said, it's about keeping your trees as cold as possible for as long as possible and limiting direct exposure to the worst temperatures...You don't look to "keep the trees warm" You're looking to keep them within an acceptable COLD range--between high teens and around 30. Simply putting them in a area out of the wind and mulching the pots on the ground with pots completely buried under four or five inches of mulch significantly "lags" extreme temps (including warm spells in the early spring--which can make your trees vulnerable to freezes after)
 

Deep Sea Diver

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@rockm You are correct, protecting the roots is job one.

Protecting the rest of the tree from desiccation, bark splitting and sun scald follows close behind.

I believe most researchers would agree keeping tree trunks below
 

Eckhoffw

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Probably don’t need the cinderblocks under the plants. Contact with the ground is probably better.
Would that bubble wrap help keep little critters out though? May not be completely useless. 🐭
 

rockm

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Yeah, the cinderblock is actually making things worse. They allow a lot of air circulation under the plant--ever wonder why there are signs on bridges warning about "bridge may freeze before road?" It's because the bridge's surface is exposed all around to the freezing air. Same thing here. Ground contact, mulch, traps ambient heat from the ground and blunts air temperature...
 

Deep Sea Diver

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…. So sorry for the miscue I was called away. Here’s the complete text

@rockm You are correct, protecting the roots is job one.

Protecting the rest of the tree from desiccation, bark splitting and sun scald follows close behind.

I believe most researchers would agree keeping a tree below 45 but above freezing would allow a tree to accumulate the necessary chilling units to exit dormancy. Keeping the trees below freezing the entire winter that’s an entirely different story.

Yet can you please clarify
“mulching the pots on the ground with pots completely buried under four or five inches of mulch significantly "lags" extreme temps (including warm spells in the early spring--which can make your trees vulnerable to freezes after)”

Are you proposing delaying deacclimation until all danger of frost is past is harmful?

I’ve been doing a daily temperature study of bonsai media in pots with trees over wintering, l mulched in on the ground, dug in and mulched in three locations vs just on the bench vs soil and air temperatures in each of four locations. So far the data does not show a significant delay in warming compared to the soil. What it does appear to show is that trees mulched in on top of the ground actually warm up slightly faster then trees dug/mulched in which warm up slightly faster then the soil temperature.

Cheers
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Deep Sea Diver

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Thanks for the photo that helps!

…. as they both said. Please take the trees off the blocks, put them on the ground and mulch in. Hope that azalea is one of the hardy ones. 😉

Open, or half open, and close the ‘cold frame’ as discussed earlier.

My experience with critters and bubble wrap is that it is a good place for them to stay warm.

Good luck
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dbonsaiw

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This hobby can truly make one crazy! Let me know if I got this right as far as set up is concerned. The ground is frozen so I will not even try to dig holes to bury the boxes. I will remove the cinder blocks from the tent and put everything on the floor. Flaps will open/close based on temp. I will head to a big box tomorrow morning, purchase mulch and mulch everything in the tent up to about 5 inches. Let me know if I got this right.

Questions: Does it matter what type of mulch? Can I purchase the $4 decorative ones that come in huge bags and are dyed?
Once everything is mulched, how do I know when to water and how do I water?
No concerns for critters and mold making home in there?
 

Dav4

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This hobby can truly make one crazy! Let me know if I got this right as far as set up is concerned. The ground is frozen so I will not even try to dig holes to bury the boxes. I will remove the cinder blocks from the tent and put everything on the floor. Flaps will open/close based on temp. I will head to a big box tomorrow morning, purchase mulch and mulch everything in the tent up to about 5 inches. Let me know if I got this right.

Questions: Does it matter what type of mulch? Can I purchase the $4 decorative ones that come in huge bags and are dyed?
Once everything is mulched, how do I know when to water and how do I water?
No concerns for critters and mold making home in there?
I’ve always used either the free chipped wood that I could get from the local tree guy or, if having to purchase in bags, the shredded cedar mulch. Honestly, you may have a hard time finding any kind of mulch due to the time of year… For that matter, repotting season is only 7-8 weeks away :).
 

Tums

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The mulch is just thermal mass so what kind isn't so important, but hopefully you could use it somewhere after winter?

As for water, if everything was moist when it froze then there's not much of a need to check until the soil thaws out. You couldn't even add more water if you tried, unless piling snow up counts.
 

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