Author Topic: Overwintering cold frame management  (Read 8311 times)


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Overwintering cold frame management
« on: December 27, 2018, 07:41 PM »
Hi Friends,

I am running a pair of cold frames for my miniature and bonsai conifers here in Zone 5a. I have about 5" of cedar mulch as a base and have mounded it around the pots. Temperature profile in the frames is excellent and it provides 10degF or more of protection at night. My concern is the humidity in the frames ... it's pretty much 90% - 100% at all times and I am worried about molds, etc.

Should I be opening the frame covers on warmer days, say when it is above freezing?

Any other advice on running conifer cold frames over the winter? My web searches have not been productive.


Leo in NE Illinois

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Re: Overwintering cold frame management
« Reply #1 on: January 07, 2019, 03:50 PM »
Yes, open the cover a bit on warmer days, leave open if nights are mild, above 25 F.

You might try adding an inexpensive 7 inch or 9 inch diameter fan. Point it toward one of the walls, so it moves air around but does not blow directly on the trees. Even a little 3 inch electronics cooling fan could work. You want air moving just enough that if leaves were thin grass, they would be constantly waving in the gentle breeze a litte. You don't need trees swaying, or flapping in the breeze. Leave fan on 24 hrs / 7 days a week.


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Re: Overwintering cold frame management
« Reply #2 on: February 13, 2019, 08:01 AM »
Most people who use a cold frame are trying to keep trees warm.  IMHO this is a mistake and could leave the trees vulnerable to early growth followed by late freezes.  These are the conditions that kill trees.


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Re: Overwintering cold frame management
« Reply #3 on: February 25, 2019, 10:16 PM »
I also live in zone 5a and use a cold frame for some trees.  My frame is 4' x 4' and goes 2' deep into the ground.  It is the winter home of my cedar elm, a couple California redwoods, pomegranate, Catlin elm, azaleas, blue Atlas cedar, some small accents , and other things.  None of these would survive winter outdoors in my zone.  I open the lid when the temperature is above 40 degrees.  Usually there is a lot of humidity in it but it dries some when I open the lid.  The only problem I have had is flooding during rapid snow melt or early spring storms.  So far no trees have ever "drowned" but it is scary to see it flooded to the top.