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Greenhouses & Garden Structures

Cold Frame For Starting Seeds?

13 years ago

I want to build an approx. 2x4 cold(hot) frame to use for starting seeds to transplant to the garden later. I live in zone 7 and it gets pretty cold here at times. A hotbed is a little too much for my needs. I would be starting 2-3 flats only. What could I use to heat it? I've looked at soil heating tapes and heat mats but don't know how much heat they would provide to the interior. The bottom will be open and the frame will be sitting on a brick patio. I don't know a lot about this. Any better ideas or suggestions?

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Comments (8)

karin_mt
13 years ago
I've had great luck with the heat mats. I use them in my unheated GH and they generate a surprising amount of warmth, especially if I have a dome cover over the flats. You might want to put something underneath the cold frame so the brick doesn't suck up too much heat. Perhaps a thick sheet of styrofoam?
rain2fall
13 years ago
Isn't a cold frame supposed to sit directly on the soil? I'm wanting to build a cold frame soon.

Rain2Fall
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Hope you don't mind if I first link to your previous post on this question since it has some info in it already. You indicate in it that your zone is 6B correct? If so you really need to add that to your sign in (see how we all have our zones listed by our names. Then someone asked in the other post what seeds specifically you are talking about? We still need that info since all seeds are treated differently. So what seedlings are we talking about? Some will tolerate full sun exposure, some will require a bit of shading to keep them from burning. But basically, in very general terms and with several exceptions, you just control the temperature. And with mixed vegetables that may be difficult to do without some shade-type covering. For example young lettuces and other leafy greens won't tolerate near the same temps as tomato and pepper plants will. Leafy greens require cool growing temps once they germinate. So this first year, depending on how your cold frame is built (not to mention the excessive warm temps we are having this year) you will be doing a lot of experimenting, trial and error learning, to discover how your cold frame works. You mention both lettuce and spinach in the other post. In zone 6B those should already be out in the garden several weeks ago since it is rapidly becoming so warm they are already starting to bolt and go to seed. Hope this helps. Dave
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kudzu9
13 years ago
like karin_mt, I use several heating mats for seedlings in my greenhouse. They measure 48" X 18" and provide about 100 watts each (about the same as a light bulb). If you use a mat in a cold frame on the brick patio it should work well...as long as you get yourself a 1" thick piece of foam insulation. Make sure the foam piece is larger than the base of the cold frame, as that will help minimize drafts out of the bottom. I also bought myself a thermostat that the mats plug into. For about $35 you can get a thermostat with a probe on a wire that goes into the soil and helps maintain a uniform temperature. Otherwise, you may have temperatures that will not lead to good germination, or possibly cook your seedlings.
rain2fall
13 years ago
How about using a soil heating cable in the cold frame instead? Again -- do I have to put the cold frame on the patio? Can't I put it on the ground, over a piece of weed barrier fabric?

Rain2Fall
karin_mt
13 years ago
Rain2Fall,

You can put your cold frame wherever it works for you. On the ground is the usual way of doing it. If you are going to use soil heating cables or heat mats then a consideration is that you'll need to run an extension cord.
grower54
13 years ago
Roger. If your hot bed is going to be raised off the floor on a frame try enclosing the legs (framework) with some scrap plywood then put a couple of 100 watt light bulbs inside the enclosure suspended below the bed. I use sand in the bottom of my raised hotbeds and it helps to spread the heat around. You can move the bulbs closer if needed. I use propagation mats now but started with light bulbs and they worked fine. Happy Planting Steve
davemichigan
13 years ago
For 2 or 3 flats you might want to consider growing them indoor with simple fluorescence fixture.

I always think of it this way: outdoor you have all the free sunlight but you need to provide heat. Indoor you have all the "free" heat (not really free but you are heating your house anyway) but you need to provide some additional light.

For 2 or 3 flats, maybe on light fixture is all you need, and they are cheap.
eaglesgarden
13 years ago
Dave is right. A single flourescent light fixture is about $10, plus a few bucks for some lightbulbs!

For less than $50, you could easily have two 4 foot long 2 bulb light fixtures, which should easily fit 2-3 flats under them. The issue then becomes where to put them inside your house. (providing a small amount of air circulation, via a small fan, or placing them in a high traffic area of the home is a major benefit as well...more breeze reduces the chance of damping off, and produces stockier plants.)

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