I have toms and sweet peppers just recently started outside on the southern exposure side and was having trouble keeping the germination temperature below 80 degrees in the day time. Heat's from a fish tank heater. In a fish tank. In a water bath. The heater has a built in thermostat but the sun's just too danged strong!

It's weird being too warm in mid December.

If you are starting under fluorescents, you really don't need a heat mat. I've done without for 50 years.

Especially for a lot of greens - such as lettuce. Lettuce will start at temps just above freezing. You can easily start it in an unheated garage under lights nearly anywhere in the country. I keep the lights on a cycle that has them come on at night, and then they're off for the 6 warmest hours of the daytime.

At 41F, it will take 15 days to germinate; at 50F, we're down to a week. At 59F, it takes 4 days to germinate. Good enough.

Tomatoes don't really need bottom heat either. In fact, germination drops off as the soil temp rises to over 75F. You'll get 98% germination at 59F, in about 2 weeks. At 68F, you'll still get 98% germination, in about 8 days. By the time you hit a soil temp of 77F, germination is down to 97%, but it only takes 6 days to emergence. But by the time you hit 86F, germination is down to 83%. If you are starting inside in a heated space, tomatoes under fluorescents don't really benefit from bottom heat, and may be harmed - in combination with the heat from the lights, soil temps are likely to rise above the best temps.

Peppers do best between 68F and 77F. Easily achievable, in a heated space, with lights alone.

Even eggplants - for me at least - do fine under fluorescents without additional bottom heat. The tables I've seen give only a 60% germination rate, tops, at soil temp of 86F - but I swear I've never had germination nearly that bad. Maybe I've just never counted, or maybe the fact that I grow orientals almost exclusively makes a difference. I'll have to pay attention this year. But I've always started them with just the lights, no additional bottom heat, and they've always done fine.

I'm guessing the sweet spot for eggplant is probably between 77F (reported 53% germination) and 86F where the 60% germination rate was reported. Also, I've no idea what type of eggplant they planted to get those measurements. I don't know, maybe some varieties really do have germination rates that low - but I'm pretty sure I've never planted such a variety.

Spinach is right there in the same range (temperature wise) as lettuce. I imagine many leafy greens are in the same range.

I really don't think a heating mat is all that useful. Better to spend the money on lights, a stand, plant trays, something to measure soil temp, and a fan, IMO. I've really not had a lot of use for a heating mat, myself.

This post was edited by zensojourner on Wed, Dec 17, 14 at 18:13

If I were in AZ I would have no problem ... but we've moved.

I don;t have room in the workshop for a grow light setup at the moment.

Still looking for a recommendation for a seedling heat mat to speed germination (or make it possible at all for the warmth-loving peppers)

I'm in the market for a heating mat as well. If you do a GW search for "heating mat" you'll find a good handful of threads on the topic with recommendations. Good luck with your seeds!

Hmmm, all I can say is that without adequate light, a grow mat is not going to be all that useful.

I'm not in AZ - not sure where that came from. But the vast majority of my seed starting has been done in the Midwest. It really doesn't matter where you are, if you are starting seedlings in an indoor heated living space. Perhaps that is not your situation.

The heat mat I recently bought was a Hydrofarm. I also bought the Hydrofarm controller. That controller has a plus-or-minus of about 2F from the temp you set it at - so the temp swing can be rather wide. I found it was insufficient to keep the soil temp at 80F at night. I did have it on a piece of 1" rigid foam insulation. Part of the problem may be that I use deep root paks, about 4.5" deep. Using a dome at night helped. It may work better with the more standard flats that aren't as deep.

Posted by lazygardens PhxAZ%3A Sunset 13 (My Page) on ...
"If I were in AZ I would have no problem"

We're easily confused.

I'm starting them in an unheated workshop in New Mexico - Sunset Zone 10. (I don't know why GW hasn't made the zone change I did in my profile)

It doesn't freeze in there, but it's definitely not tomato or pepper starting temps.

We want an early start on the peppers, will put them in a temporary greenhouse for growing them out.

I'm planning on low tunnels and plastic for the seedling leafy greens.