hey al .. ignore the idiots ... life is too short to be irritated by them... you said: So what part of Zone 5 are you in that you can plant early May? i said to start them about 4 weeks prior to last frost ... i see my sentence was rather vague .. lol ... but let me clarify further ... they need to be about 4 to 6 weeks old when they go out .... so to that you should add how long they take to germinate .... and i dont have that info off hand .... as noted.. its on the pack.. lol ... i am in adrian MI ... just south of ann arbor ... and out here in the country.. last frost date is reliably the last week of may ... and since the 'rent anniversary is 5/25 .... i can say that we have used that date as our plant out date for the 40 years i have been paying attention .... mx is in metro Detroit .. and z6 [ i have a theory about retained heat by cement causing the increased zone] .. i really question her comment that she is frost free around 5/1 ... take that with a grain of salt .. as i can see her out there building little TP's on a cold-forecasted night .. she is totally a full contact gardener ... petal to the metal ... she will get away with a few things that some of us who are not as full contact ..... only you will define were you are in that spectrum .... in my world.. i plant them out ... when i dont have to worry about them ... otherwise i leave them in the closed garage at night .. last year all the neighbors were bemoaning a late poor crop of tom's .... and we decided a late cold spell retarded proper flowering and fruit set .... after a very warm .. hot april ... may was back to march temps .... tom's are all about soil warmth.. and last year.. it was out of phase ... but in the case of tomatoes ... they are VERY.. VERY susceptible to frost ... so i would hesitate ... after investing all that effort to grow them... to not be sticking them out too early ... good luck ken

LOL! Well, here in Salt Lake County, UT, we have long winters & summers, and short springs and autumns. It's weird; things start warming up in late February, but there are a lot of false starts, and it's not uncommon for us to have a lone snow storm in late April, even if we hadn't had snow in weeks. I don't know the spring frost date off hand. Judging by the sources on the web, it's probably somewhere between 4/18 and 4/26 (one site said 5/18, but I think that's way off). If 'spring frost date' literally refers to the average date of the last frost, then late April seems plausible, as Winter often takes a dying gasp around then. But generally, frosts are few and far between by then. If we have a frost in late April, it usually follows a week or two without frosts, so even though late April might typically be the spring frost date, I don't know if that's the best date to go by (maybe you guys can help me figure this out). I mean, the average low creeps above freezing by March 11th, according to Weather.com. I know that this is only an average, and that in any typical year, I can expect several frosts after this date, but late April still seems a bit late to me. But what do I know? Over the last few years, I bought my tomato plants at the garden center, and I always waited until May to plant them.

MaryMcP, you make important points. Soil temp can be a killer, especially in hot climates, because in hot climates. our tomato growing season is short. By late June, I'm all done for the summer. I chuckle when I hear northerners taking pride in getting their first tomato by the Fourth of July. Getting tomatoes in the ground outside for us is a race against the eventual heat. That said, the Syngenta tool says that the average soil temp in Phoenix on March 1 is 60F. Pretty much like for me. So some years are harder than others. As to why folks don't start new threads, and instead glom onto archaic ones, should we suspect it's shyness? Now, I answered that original thread because I didn't notice that it was old. Is this your question, or someone else's question? Some resurrected threads here are old enough that the people that started them are probably well composted.

I think you should grow them in a greenhouse on heat (propagation) mats. You can get heat mats with or without a thermostat. This will warm the soil. You will need very little supplemental heating unless the temperatures dip down below freezing. As long as the roots are warm your tomato seedlings will grow. As far as cooling, there are many different ways to cool a greenhouse automatically and even without electricity. For sure your greenhouse would need roof vents with solar powered openers. A second option (and the way I start my tomato seeds every year) is to grow them inside. I have a indoor plant stand with fluorescent lights. I put the lights on a timer. I put my seedling trays on a heat mat. Works every year! But, I only start about 25 plants. You would need some room to do as many as you grow. As far as solar powered heaters, I don't know of any. But, there are greenhouse propane or natural gas heaters that require no electricity. You could have a propane tank put on your property to supply it. I am in zone 8 in Louisiana.