Cold Frame For Starting Seeds?

14 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
14 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
14 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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The lettuces, spinach, kale and cabbage would be fine out in a coldframe. I've been growing all 4 of those all winter long. The spinach has been doing quite nice. The warm season stuff cucumbers, tomato, squash and melons are okay in the coldframe but not until 2-4 weeks before your last frost date. If you put them out earlier than that they may get too cold at night and become stunted. Unless maybe you want to have a heated coldframe which is them called a hotbed. I use Christmas lights for extra heat. I thought about the buried cable option but I have a way of accidentally digging up things that are buried. As digdirt said coldframes/hotbeds are something that one needs to monitor every day. I use 4 different methods. The frames wide open for days above 40F, cracked open about 3 inched for days 30 to 40, cracked open 1/2 inch for days 25 to 30F and closed fully below 25F. Just harvested a bunch from this frame. :-)
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I only have one heater in my cold frame and it is a 150 watt element with no fan. The reason I installed a small fan in the cold frame was to distribute the heat and get even temps throughout the cold frame. I st?arted the lettuce and spinach in the house and kept the temps 70f. Therefore, since they were only two weeks old or so, I figured I needed to keep them around 60-70f. What do you think
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Hi Jackie: I assume you mean a greenhouse if you can walk into it and not a cold frame. A cold frame sits low to the ground and you can't walk into it. It would help if I could see a picture of it, but I'll go on the premise that it is actually a greenhouse. I have had a homemade greenhouse for many years and I think I can give you a few tips. First make it as air tight as you can. Next is there any way you can section off a piece for seed starting. You don't need the whole greenhouse to start seeds and there's not much use heating the whole thing. A floor of stone or cement slabs or a combination of both will also help retain heat in the greenhouse. Often in old greenhouses you will see a brick or stone wall on the north side. That was not just decorative but also a way of heating the greenhouse at night. There are 2 things I think You should consider buying. One is a minimum-maximum thermometer, and the other is a heater with a thermostat. The minimum-maximum thermometer gives you the lowest and highest temperatures since it was last set. This allows you to set the heater so it stays above freezing and lets you know when it's too hot and has to be opened. I live in zone 3. I open my greenhouse in mid Apirl. Our last freeze date is the end of May, so I would say you are just about right starting now. By the way I figured out it costs me around $50 for the season to heat my greenhouse with an Electric heater. You have discovered the magic of a greenhouse. Yes it can be below freezing and if the sun is shining it will be too hot in the greenhouse. I try to keep mine in the 70's in the day, but at night it can go down to the low 40's. If you don't want to heat at night, then have something you can cover your plants with when the thermometer dips very low at night. During greenhouse season I watch what the temperature is going to dip to every night. I do recommend you get the thermometer. It will be a great help with knowing what you have to do. If you have any more questions post them and I'll be happy to answer if I can
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kudzu9
14 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
14 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
14 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
14 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
14 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
14 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.)

Cold Frame For Starting Seeds?

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karin_mt

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