Bob,

I would probably build a crude cover for them of a night, at least until they germinate. Could be as simple as draping a blanket over four-six milk crates. Your soil can lose a lot od warmth of a night. Once they germinate, temps in the mid-upper 40s won't harm them at all.

Mike

I'm not sure what you're starting, but I keep my seedlings in an unheated garden shed, and at times we've had nighttime temps down in the 30's. I've got tomatoes and peppers growing, which are heat-loving. I did germinate them in the house where we keep the temps around 65-70. But the moment they sprouted, they went out in the shed.

Though I have heat pads, I haven't used them this year. I've found that my seedlings are getting enough heat just from the shop lights. I've also made a box around them to hold in the heat, using foam core insulation. I've got a small fan that I run on them every other day, during the day only.

Last year, I used the heat pads and fretted over temps a lot. This year, I tried putting them out in the shed and I've been pleased with the results. I'm not having any problems at all. Granted, I've started my seedlings a little earlier than "the books" tell you. I think the only hazard of having them a little cooler is it slows down the growth a bit. But I've compensated for that by simply starting earlier.

Here's some pics of the set-up:

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Here is a link that might be useful: my blog

You don't indicate what seeds you want to grow, but most will germinate fine but as soon as germinated will need light. The fluctuating air temperatures should not be a problem with your pots on your heating pad. My unheated greenhouse varies in temperature from about 45 at night to up to 70 during the day. My bottom heater maintains about 70 degrees and germination is not a problem. Al

Thanks all for the input and great suggestions! Solves a lot of issues. Now if I can just get my leggy shoots under control.

leggy shoots - means the lights are too far away or just not enough light. they are looking for more light

Yes - unfortunately I realized this too late. I had the seeds tucked away and didn't realize that they had sprouted until too late. I'll do some transplanting and bury them (mostly tomatoes), hopefully not all is lost.