Building Cold Frames

11 months ago

last modified: 11 months ago

Camille was asking about cold frames and this seems like the best place to share the information.

While cold frames can be built with old windows and they will work it is high maintenance as the window aka "the lights" need to be opened at least partially every sunny/part sunny day and then closed again late afternoon/evening. While forgetting to close it might not do harm forgetting to open it on 37 degree sunny day and probably every plant will be toast.

To get around this what's needed is an automatic vent, I've had good experience with Bayliss vents

https://www.amazon.com/Bayliss-Greenhouse-Autovent-XL/dp/B0027DJ5RM There are other popular brands such as univent

The wire is there is to stop rabbits or cats getting in.

Now that an opener is obtained it needs to be installed. It takes basic wood working skills to fit it into the lights. I prefer double wall polycarbonate. I found a place locally to buy as shipping large sheets is expensive but here's a peek at some from The Mighty A https://www.amazon.com/Polycarbonate-Shatterproof-All-Weather-Greenhouse-Covering/dp/B08KNMHWHS/ref=asc_df_B08KNMHWHS?tag=bngsmtphsnus-20&linkCode=df0&hvadid=80470624768979&hvnetw=s&hvqmt=e&hvbmt=be&hvdev=c&hvlocint=&hvlocphy=&hvtargid=pla-4584070153224742&th=1

Some screws, 1x2s, hinges and wood glue put the lights together. I won't go into detail on that. Here's a picture

A system will be needed to secure the lights when fully open. I've used a log with a inserted piece of rebar then pushed into the soil. A metal hook in the log and bungee cords to the lights hold it in place.

I'll post this now and continue when I have more time.

Comments (3)

gjcore
Original Author
11 months ago
Once the top is built the box need to be built. It's a very basic wood structure. I like to hold the pieces together with screws and corner braces so I can take it apart and store it during the warm months. The front side should face mostly south to somewhat southeast. The slight southeast orientation will allow it to warm up a bit faster on those cold winter mornings. I've done the south side of the box frame a few different way. Early versions were wood. The downside of the south side being wood is that it creates a shadow behind it which can be fairly long with the low angle of the sun during the cold season. That was the way all instructions I saw in books or the net. Now I use polycarbonate or greenhouse film for the south side which eliminates the shadow issue.

When fitting together the lights and the box there's likely to be some gaps. First I rig up this bungee cord system to strap the lights down to the frame and then give a good look around. The bungees also hold the lights in place should the wind get strong.

It takes a bit of experimenting to get a fairly tight seal around. I've used weatherstripping, silicone with paper and greenhouse film stapled about. It's not necessary to be air tight but not too much airflow from the outside is best.

To be continued...
treebarb Z5 Denver
11 months ago
Greg, this is awesome! Did you use a full sheet of the poly and build the box to fit the sheet size? What months do you grow in it and what plants?
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What are you planning on using for your glazing (or top covering)? How are you planning on opening your cold frame when it gets too hot inside? I'm going to assume that you have typical 8x8x16 cinder blocks. I would probably remove your cinder-block side walls and use plywood instead. I would frame the top of the back-wall and front-wall cinderblock with a 2x8 board. I would then put a piece of plywood to frame the two side walls with a 2x4 sideways to act as "joists" for that angled side wall (near the top). You could use the extra blocks to make your cold frame larger or for another project. I would then frame the glazing with 1x2 boards with weatherstripping on the bottom so that when it rests on your 2x8 or 2x4 boards you get a mostly weather-tight seal. I would hinge the top and add an auto-lift-vent to the bottom. If you plan to continue to use your side-walls I would modify your top row so that there are no bricks going forward. This would give you a relatively straight run from the front of the bottom bricks to the front of your top bricks (going up 8" for every 16" horizontal). I would still then cap the ends with plywood and do what I recommend above with 2x8s on the front/back cinderblocks and a 2x4 on the side to support the glazing. At your discretion you could add 1 or 2 liter bottles filled with water into the holes of the concrete to help stabilize the temperatures (assuming the tops are capped with a 2x8). I believe your structure gives you 4ft x 2ft floor space. For all this work (and if you go with the auto-vent) you might want to consider going larger if possible. :-)
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gjcore
Original Author
11 months ago
last modified: 11 months ago
I purchased the poly from a warehouse in Denver and had them cut it 4' x 7' because they had 4' x 28' so that seemed like a good size to fit into the truck and for a garden bed. Generally the box is built once the top is built.

During the cold months October to April I'll grow lettuce, bok choy, mizuna, mustard, rosemary, parsley etc. Basically any green but especially the Asian greens. Sometime in April I'll move to frames to another bed. This year I only moved 2 of 3 of the frames. In one I have sweet potatoes and the other peppers. I should have moved the other as well but there have time constraints.

Cold frames are also excellent for hardening off. Most things I'll move straight from under the indoor lights into the frames. I'm a bit more cautious with the late spring hardening off. I'll put some agribon on top of the polycarbonate for a few days. Not sure if it's necessary or not but it's the current system.

Building Cold Frames

Comments (3)

gjcore
Original Author

treebarb Z5 Denver

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Building Cold Frames

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treebarb Z5 Denver

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