Building Cold Frames

3 years ago

last modified: 3 years 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.

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Comments (3)

gjcore
Original Author
3 years 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
3 years 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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gjcore
Original Author
3 years ago
last modified: 3 years 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.