Winter Care below 20deg F

I am in NY. I have Juniper, False Cypress, Boxwood, Chinese Elm and Holly trees that I have built a shelter for next to my house…it has a wood roof and walls made of 4mil clear plastic. All plants are heeled in with mulch.
If we have long stretches during the winter under 20 deg F, should I move them to an unheated garage (no light)? If so, what would the threshold be roughly to do so (how many days below 20)?


Hi @FredGrau
Do you get a lot of snow? It may act as an insulator. Also worth getting a max-min thermometer for inside the shelter

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We only get a few good snowfalls that stay around. Also I have a roof on my shelter now. What temp would be a minimum prolonged point to put them in a garage? Thanks again Andy.

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I have a mixed herd. Juniper, boxwood, elm, holly, dawn redwood, jap larch, mixed pines, etc, etc…I keep most of my small decideous trees under my large kiwi arbour after leaf loss, mulching high with maple leaves early whhen temps <35F. Penned in with plywood panels. When temps <10F hit , they get covered with tarp.
Good to <-15F?. Never lost trees to freezing…? Maybe 1 or 2 unknown winter loss. (Rem: put out rodent poison in covered containers. VOLES .)
Temps this week at 12F low. 35 high. Thermometer reads 30F on bottom. Perfect. Won’t worry until I temps hit >45.

Sulfer spray if you see problems. I have not.
Evergreen and large decedous trees go into a cinderblock U behind my garage. Summer bonsai benches…,. Some leaves for decedous part. I leave it open on top to let snow in. GOOD INSULATION and moisture control. We have not had show yet. DONT LET COMPACT TOO DEAP. When it gets cold <20F, tarp over top, using 2x6 support.
Make sure the top comes off if it hits>45. Thermometer in pot at bottom in early spring stays <32. Perfect.

The only time I lost obviously winter killed trees was when I brought several into my garage. Large black pine, horse chestnut etc…Probably desicated by sublimation. No snow…

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Hi @FredGrau,
I don’t really have a rule of thumb, but air on the side of caution, better to be safe than sorry.
@KurtP Absolutely loving you duel usage of cinder blocks and bench planks! Efficient and graceful!

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Awesome set ups, thanks Kurt!

Last spring i caught a little mouse eating the bark of the deciduous (cotoneaster, burning bush / Euonymus alatus, and Potentilla) trees that were mulched at ground level in a lean-to green house. We were unwilling to deploy chemical warfare due to the risk to the other locals (bunnies, cats, doggies and such) as a result i lost the Potentilla, Cotoneaster, and gained a bit of character to the nabari of the Euonymus. If the invader makes it to my older elm or Korean lilacs this year, reinforcements may be necessary. The side wall were the vermin were attacking from has been reinforced with soil, but we did not want to completely seal up the French drains for fear of impeding drainage from spring melt. I also removed the bedding (bags of oak chip shavings) where they were likely residing but have not employed mechanical traps. I had no idea mice would eat bark. Is this a common occurrence and how paranoid should i be about the pines that are wintered in with everything else? Geenhouse%20trees Geenhouse The%20trench%202nd%20angle
I too appreciate the cider-block bench plank construction. We are in SW Montana and have stretches of temperatures well below O F and my winter losses in the unprotected trench seem to be due to improper fall preparation (lack of fertilization???) rather than freezing roots. However, spring root rot from improper drainage cost me a massive urban yamadori mugo pine several years ago. Any thoughts would be well appreciated as winter paranoia seems to be a dangerous activity.


Mice n voles… killed 45 decideous bonsai several years back…I have small styrafoam soup cups with lids, cut a small v in side. Rabbits also eat ANY bark during high snow winters. I had about 40 Utah oaks in the ground. They kept them about 1 foot high… Then the neighbors cat got a taste for meat… Now the trees are 10 feet. They also ringed several other tall pre-bonsai trees…
Squirrels… eat EVERY nut I plant for oak forests… Also eat the new growth of the trees… even older established oaks… down to the nubs… hmmm… squirrel stew…
GOTTA LOVE BONSAI ING…:persevere::blush:


I have about 8 cats outside in my yard, youbthink tgey will handle the mice and mikes? I certainly don’t to poison the cats.

I had chickens… they died of old age. Now i have mice and voles. Neighbors cat cant keep up. Hawks too…
Put the bait out inside of covered trays. ONLY in with the bonsai storage… cats wouldnt eat it anyway. Keep kids from handling it though…
Cats got the rabbits here… they ringed several in-ground trees… :hugs:
How do I stop these squirrels… without killing em…


The thing with squirrels is any deterrent used needs to be placed before any eating habits/patterns are formed.
If the squirrels have been chewing on your trees, it’s too late for deterrent. This is when you would use a mesh screen, 1/2” by 1/2” works well, to protect your trees.
Good luck.

Trouble is… I like em … ( not so much worried…)
Even IF oak acorns and hazlenuts are planted over 5 acres… Just leave my BONSAI alone!,
Fed one scrawny half tailed female two winters ago. Five lbs of white oak nuts…Now there are 4 squarrels…

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I simply keep mine in an unheated garage, and cover the soil with mulch. Some trees are dug into the ground (i.e. with their pots). Have maybe lost a rhododendron and a japanese maple, and some saplings in their first winter (grown from seed), but otherwise no problems. Most of my trees are winter hardy here in Norway. It normally gets down to 14 F (-10 C) and occasionally -4 (-20).


So gestation for squirrel is 45 to 50 days… so you can have several hundred in a few years. You are taking up a huge responsibility if you plan to feed them all!! :sweat_smile:

It snowed on monday, 12F, I threw snow on top of my decideous trees and tarped the evergreens.
Today it was 40F and rain. Took the tarp off… snow melted. My lilacs buds are swelling…
I need a new hobby…


:grin: It was a comfortable 22F here last night…Bismark ND was about -50F ish.
Just FYI…At about -60F, pines can explode… I have heard it several times… (North Idaho in the mountains…)
Oh ya, mercury freezes at -37.89 F…
Squirrels are doing fine…

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I assume you meant negative 37.89F
Mercury · Melting point

-37.89°F (-38.83°C)

Yup. Bad editing…when it matters…!
Trivia, deg. F And deg. C meet at -40…
+35 F here… yaay!

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I live in northern Vermont. Big proponent of unheated garage as an option. My best trees however, are stored in winter greenhouse with temperature controlled environment, but the balance (25 trees +/-) I place on tiered metal storage racks on wheels in my unheated garage. Two windows provide some light, but my understanding is that the trees do not necessarily need light while dormant. Temperature in garage gets down to low-mid 20’s when temperature is below zero outside, high 20’s to low 30’s remainder of winter.

Started this 9 years ago with several mature junipers, plus 60 one year old seedlings (mix of mikawa black pine, red pine, crabapple, japanese maple, trident maple) which I potted up. Pots were packed in mulch inside large tubs. 99% made it through 1st two winters. No longer pack any trees in mulch. Rarely lose a single tree (maybe 5 total in 9 years). Love seeing the trees bud out in March.

Try it. Just don’t put all your eggs (trees) in one basket the first go around.

Note: Advantage of tiered metal storage racks on wheels: In early Spring (early to mid-April) I can easily move them outside early morning (assuming no wind and reasonable temperatures), then wheel them back into the garage when I return home from work…and back out again the next morning…gradually re-introducing them to being outdoors…until they can remain outdoors for the season (sometime in May).


Been a cold snowy February.
5F tonight. Windy, wind chills >-15F.
Been >35F for 2 weeks, nights down to 0F.

Bottom of the decideous bonsai pile is 23F. Happy campers.