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Do cold frames work to overwinter trees in pots in Zone 3?

I will have some small potted trees to overwinter this year.

My garage is too cold during December, January and February. So I was thinking about some sort of cold frame, against the outside of the house. It would be 2'x3', sunk in the ground 12" so the top is flush to ground level. I could put 2" foam board on the bottom of the 3/4" plywood door for insulation. The sides would be 1.5" treated lumber back filled with soil. Of coarse, it would be imperative that snow fall is sufficient to pile a deep layer on top of the door to keep the extreme cold out. That or put bales of hay/straw on the door for insulation.


My question is, does anyone my/our zone (-35dF), or colder, winter potted plants outside? And to you use an enclosure similar to what I described? Or how do you do it? Does it stay warm enough (above ~20d F) so that the roots don't freeze? These would be zone hardy trees I'm talking about not sensitive to our temps.


I'd like to hear from people that have actually had success or failure doing this, so I can out what works and what don't.

Comments (11)

  • mntreegrower

    While not quite as cold as you may get, I have over-wintered trees in pots for many years, Bill. But what I do is sink the pots into the ground in the garden and then mulch them with leaves and grass clippings for insulation. In the spring, I dig them out again so they don't start rooting like mad through the drainage holes in the pot bottoms. I have never lost a tree doing this so far.


    Not the response you were asking for but I figured since no one else had responded yet...

    Bill_minn_3b {West Central MN} thanked mntreegrower
  • Bill_minn_3b {West Central MN}

    Thanks!

    I'm thinking there's a reason no one has responded, probably bc no one does it. :-)


    It would be better, I think, to have an old style 'root cellar' type, where you were actually under the ground, there it stays 40d F all winter. I'm thinking a shallower 'cold frame' would still need some kind of cable and thermostat, for those few winter nights with no snow and sub zero cold enters the picture.

    So it's getting to sound like too big of a deal to mess with just for keeping a few pots. I may make a small cold frame anyways and use it early spring when I start putting things outside.


    I'd love to hear what you do for rodent protection, every time I start piling leaves/grass, it's mouse city around here. But if it's a company secret, I'll understand. :-)

  • mntreegrower

    I put trunk protection on maples, crabs, and anything else that has been chewed on by critters in winters' past. White corrugated protectors or the flat style that can be wrapped around the trunk. The flat style is nice because it can hug the ground and lessen the chance that rodents can squeeze in underneath and have room for a nest. I suspect neighborhood cats, owls, etc have also been helping out.


    Be careful if you choose to winter the pots in an area that will always stay above freezing. Without some moisture, the pots can dry out too much and the trees could be dead come spring.

    Bill_minn_3b {West Central MN} thanked mntreegrower
  • Bill_minn_3b {West Central MN}

    Might take me some time to figure this one out. I could leave them in my unheated garage until late November, depending on how soon the cold comes. Then move them to the basement where it normally could be as low as 50d by then and could be made even colder with an open window. Then move them back to the garage end of February.

    Dunno. Have to think about it some more and is it really worth all the work to do that.

    Could just dig them into the ground and put a pile of mulch on top and a tote over that with a few bricks on top to keep the mice out. And if I put all that in the same area where I was placing the cold frame, it's out of the sun so any snow piled on top would stay a long time. IF we get snow.

    No hurry so there's time to think about it.

  • Bill_minn_3b {West Central MN}

    Doesn't look like I'll have any potted trees to overwinter after all. So I'll give this one more time, maybe do something about it next season. Thanks! :-)

  • mntreegrower

    Lucky you, Bill! I planted too many seeds and seedlings in pots a few years ago. I didn't expect so many to take AND grow so well. Now I have too many trees to give away and not enough people to take them. Why do I continually do this to myself? :D

    Bill_minn_3b {West Central MN} thanked mntreegrower
  • Bill_minn_3b {West Central MN}

    I'm already seed collecting for next spring. We might see this thread pop up again before next season. :-)

  • Bill_minn_3b {West Central MN}

    Ended up putting in a small, below ground frame. Not so much for potted trees but I had some seeds with long stratification needs so thought I'd try planting them now and letting ma nature do her work over winter. My garage can get sub zero temps so not the best there.

    Might have to throw a foam board on for insulation if we don't get snow by December.

    I'll find some use for it no matter what and it's in an 'out of the way' location so no problem. Crappy phone pics but you get the idea...



  • mntreegrower

    What sort of seeds do you have in there?


    I am not too thrilled with the temps going down below freezing tonight. While new growth looks done on everything here, some of the branch tips don't look like they have completely hardened off yet. Lacking that "woody" appearance still.

    Bill_minn_3b {West Central MN} thanked mntreegrower
  • Bill_minn_3b {West Central MN}

    Last year, some of my maples didn't look hardened off but came through just fine. Sometimes an inch or two of leader tip will die but it doesn't seem to affect the tree at all.


    OstryaVirginiana, CeltisOccidentalis, Tsuga canadensis and Thuja occidentalis. I have extra seed inside that I'll stratify in the fridge in March. Wanted to try this to see how it works. Could be a real time saver.

    My Gleditsia triacanthos from seed, came out good from this spring, It's looking like a good way to get some trees I wanted. This picture is from the end of August. I planted several out on my land in the country and gave a bunch away to a local nursery. Over 2 ft tall and wasn't germinated until first part of June. Looks hardened off lately.


  • Bill_minn_3b {West Central MN}

    It's in there somewhere.

    We got over a foot of snow the last couple of days.

    Just in time for the cold weather they're predicting.

    -14d for tonight.


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