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I made a cold frame out of $5.00 worth of lumber and some saran wrap. I don't know if it necessarily deserves the title "cold frame", but I want to use it as a place that is protected from the elements where I can sprout and keep seedlings during the day.

I know that one usually uses a cold frame to raise early lettuce and other things in, but is a cold frame an acceptable alternative for a greenhouse?

winwaed
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Peter Turner
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2 Answers2

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You live in a similar zone to me so we have the same issues with seedlings. When they are young they are sensitive to cold and burn easily in hot direct sun. If you put seedlings outside when it's too cold your unheated cold frame will not protect them very much.
If you put your seedlings outside on a warm sunny day it could get too hot and bake them.

A greenhouse can have heating and should have ventilation which takes care of a wider range of temperatures. I think your cold frame will be useful for a few weeks in the spring and again in the fall for that period of time when you could still get a frost but it's not too hot.

kevinskio
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    ... and even then it will be really easy for it to surprise you by overheating, at least until you have a few years of experience with it. You're much more likely to have problems with damping-off because of the high humidity in it, too. – Ed Staub Mar 09 '12 at 00:51
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Seems like it would depend on what you're growing, where you are, and what the weather is like.

You say "during the day", are you bringing them in at night? If so, and you've got enough sense to keep the plants inside during a cold or windy/rainy/snowy day, then you're probably ok to put them out. I got a tiny "mini greenhouse" for Christmas -- basically a clear plastic tent that goes over a little frame -- that I plan to use in this way for hardening off before planting out.

I wouldn't put my tomato seedlings in a plastic wrap cold frame in Wisconsin in early March. Tomatoes are tender, and I'm guessing that you're still getting some fairly cold nights. (20°F overnight probably isn't outside the norm?) Your cold frame isn't going to hold much heat. The tomatoes will be dead in the morning.

If you were growing spinach in South Carolina, and the overnight temps were expected to be in the 40s°F, then I'd say go for it.

I wouldn't try to germinate seeds in the ground in a cold frame at this time of year. The soil is probably still pretty cold, and the seeds will germinate slowly, if at all. You're better off inside.

bstpierre
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  • I've got one of those mini greenhouses. The plastic is in shreds after the third year, hence the cold frame. (at least now I don't have to worry about venting my greenhouse) – Peter Turner Mar 08 '12 at 21:09
  • Thanks for the info. Mine was a gift from the local overstock ("junk") store so I'm not expecting too much, three years will be good! – bstpierre Mar 09 '12 at 12:36