My New Cold Frame


Many gardening books and blogs and seed starting tutorials will tell you that If you’re going to grow things from seed, you really must have grow lights if you want to avoid ending up with sad little spindly seedlings. In the past I’ve been pretty successful with seedlings grown on my south-facing windowsills without the help of grow lights, so it certainly can be done.

This year there are so many things I want to start from seed that I probably don’t have enough windowsill space for everything. Still, I didn’t really want to spend a whole bunch of money on grow lights, and I don’t know where I’d put them in my little house anyway, so I decided to go with a low-tech solution. Scott found an old window at the dump and some old boards in his attic, and put together a nice little cold frame. It cost zero dollars and took maybe an hour.


I moved my little onion seedlings out there on Friday, along with some mesclun, kale, chard and other greens that I started a few days ago. It’s about 36 degrees here today, but inside the cold frame it’s a balmy 60 degrees. It does get cold in there at night, but the cold frame does offer a few degrees of frost protection, and the onions and greens are cold tolerant crops, so they can handle it. Hopefully we’ll be eating salads of homegrown baby greens in just a few weeks! Next fall I’ll use the cold frame again to grow greens through the winter.

Another advantage of the cold frame is that the seedlings are being exposed to the elements from day one, so they won’t need to be hardened off before they’re planted in the garden. They’ll be stronger than seedlings that spent their first weeks being coddled indoors.

Hudson Valley Seed Library has a tutorial for building a cold frame, and another for starting seeds in one. They suggest using a clear corrugated plastic material for the lid, but you can also use an old window or even clear plastic sheeting stapled to a wooden frame. You just need some sort of frame, and some sort of transparent lid that you can open and close, and prop open on warmer days so that your seedlings don’t cook.

Here’s another one made from a window. You’ll notice most cold frames slope downward in front. This gives you maximum sun exposure. We didn’t really think about this, so mine is flat just because it was easier. Less cutting and less math.  I was looking at mine this morning and noticed that the front of the frame casts a nice long shadow over the inside of the box. This will be less of a problem in a few weeks when the sun is higher in the sky, but still it’s probably best to suck it up and do it the right way.

9 thoughts on “My New Cold Frame

  1. Haha! I also have a flat-topped cold frame. It’s so much easier, since you can just set the lid on top instead of having to hang it on a hinge. If I had to do all that, I’d have no cold frame at all! So I’m happy with my little guy. I’m hoping to move some lettuces out there this week. (Like you, I have pretty good success with my south-facing windowsills, but lettuce is the one thing that really seems to need to be outside…)

  2. Hey! It looks fantastic! What a great score getting all the materials for free, on top of cutting back on a few more things that won’t go to a landfill.

    You’re so right about a flat-top being easier and less math -ha! If you’re worried about the shadow for now, I wonder if you could temporarily prop the back end up on bricks or cinder blocks or something to raise it a bit and then fill in the gap that would be created along the ground with more bricks, stones, or juice/milk jugs filled with water (they’d retain heat during day and help add heat at night as well as block wind.) Just a thought.

    Good luck with all those seedlings! I’m about to start round 2 of my winter sowing next week!

    • Thanks! Yeah I think we might try something like that if it seems like the seedlings aren’t getting enough sun.

      I laughed when I read your post about building a cold frame, because I totally would have screwed up the whole angle thing too!

  3. The coldframe looks very smart, and I think you should get extra bonus points for re-using and re-cycling! I’ve never used grow lights either, the seeds and plants don’t seem to have suffered from my lack of electricity in their lives, just a plain sunny windowsill too :)

  4. Some friends of mine have had a cold frame just like this for years and it works so well. Easy to prop open on warm days, insulated enough for this time of year. I’d much rather grow seeds this way than with grow lights, heating pads, and fans indoors. By the time you buy all of that stuff you might as well buy the plants!

    • I agree! I hate the idea of having to buy a whole bunch of extra equipment, not to mention the extra electricity to run it all!

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