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Cold frame management for container conifers (6 Replies)

Posted November 27, 2018 at 1:28 pm

Hi Friends,

I am a first-year conifer collector (with 20 years as a forest ecologist) and I have two cold frames for the plants in my collection that are Zone 4 and higher. Location is NW Connecticut and they are situated on the north side of my house. Since my soil type is riverwash (we live next to a river), I was only able to sink the frames about 4″ into the ground. I mulched all around the frames to about 6″ – 8″ above ground and added 4 intact bags of mulch to the front. There is about 4″ to 5″ of mulch inside. The entire assembly is underlain with hardware cloth turned up around the outside edges of the frames. During last week’s 2degF overnight low, the interior mulch temp never got below about 20degF.

My plants are in the cold frames, but I am concerned about moisture buildup in the frames … there is a lot of condensation on all surfaces. I have three questions:

1. Should I be opening a window or two periodically to let some of the moisture vent to the atmosphere?

2. I have a nursery thermostat and the heating pads are set under the mulch in the frames. I currently have them set to keep the temperature to no lower than 15degF. Sound right?

3. Should I add more mulch to the interior?

Also interested in any other opinions/advice on this setup and its maintenance across the winter.


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Posted December 13, 2018 at 9:49 am

In case anyone is interested:

No heating pad assist. The heating pads turn on when the coldframe temp reaches down to below 15degF and likewise they turn off when the temp rises above 15degF.

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Posted January 11, 2019 at 1:18 pm

Harry , <>I can’t believe no one has responded in 4 weeks ,,, I don’t come over here enough – only when things get slow over at gardenweb conifer forum ( google it ) anyway ,
you are over loving your plants ,, unless some are rated 6 or higher , you don’ need added heat
I would leave your frames open except for the coldest nights ( below 0 )
are your plants going in the ground eventually ?

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Posted January 11, 2019 at 1:27 pm

By the way , Harry , REAL nice cold frame setup,,,, and is that just one season’s purchases ?

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Posted January 14, 2019 at 8:12 am

Hi Ron, Thanks for the reply and the gardenweb conifer forum lead.

Most importantly, thanks for the advice on venting the frames in moderate winter conditions.

I figured that I might be being too obsessive over the plants. Most of those in the coldframes are zone 4 and 5 and I figured that being in zone 5, I needed to use the +2 zone rule for containers. The heat pads have yet to be activated – last night it was 6degF here and the frames stayed a cozy 19degF with no supplemental heating.

I just finished my first year focusing on miniature and dwarf conifers. I previously had some conifers in container culture including some large specimens and I have a number of alpine troughs of various sizes, all with one or more miniature conifers. In 2018, I added many new small ones and also obtained part of a container collection of a collector who had to give up his plants because of a move to NYC. Some of his specimens were quite tiny and pot-bound and I probably repotted 1/3rd of the plants in the photos last year.

As for outplanting, yes, that’s the desire. I am trying to figure out a solution as my property’s soil type is riverwash and I have to do a lot of soil augmentation. Thinking of mounds and the like, somewhat alpine-garden style. That’s the #1 mission for 2019. I’m trying to deal with overall design right now, reviewing a lot of the ACS gardens highlighted here.

Thank you again!

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Posted January 15, 2019 at 1:12 pm

Harry , If you would have gone to gardenweb , your question would have been answered in 4 hrs.,,,although we still need to frequent this site ( it’s good for clicks or some thing,,, ??)
post these pics at the conifer forum ,,,lots of peeps will love these
your plants need to go dormant and stay there,,,the mulch & frame are enough to keep your babies comfy ,,, I think the 2 + zone would be for exposed pots
I don’t know what riverwash is,,,,mounds rule
ron ( plantkiller on the conifer forum )

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Posted January 20, 2019 at 6:20 pm

Great, Ron, thanks. I will see you over at Gardenweb. BTW, riverwash soils are basically cobbles and stones with some normal soils filling in the spaces. It’s a typical riparian / streamside soil.

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