I second the "there are way too many factors" to be able to determine how many days until harvest. Further, with "tenders," there are some varieties that are more adapted to colder nighttime temps, I think that those are the "early" versions, in tomato-speak? I have one variety this year that is supposedly 50 days, so we'll see. Of course, I have one variety of seed in my stash (I've never planted it) that is supposed to be so reliably self-polinating, and able to tolerate much cooler temps that it's supposed to be able to bloom and set fruit before you even see the bees. I can't remember what it is called offhand (maybe an "Arctic" variety?), but I do remember that what research I was able to do indicated the flavor wasn't worth the plant taking up a spot in my garden. All I know is when the first 'mater comes, it happens, and I can't wait to sink my teeth into something better than the pink mealy things that I occasionally break down and have in the wintertime. I'm in the beggining to harden off phase with my seedlings now, and my babies braved the cool last night--I think it got down to 57, which was warmer than the predicted 50. Do you think 3 degrees would make a difference, had they been planted out? This is where the debate really gets silly (considering the "all other things are never equal" angle), does 59 matter? what about 58, 57? 55? When does that extra degree REALLY make the first harvest later? Ultimately, I use the "days to maturity" as a guide to try and figure out which tomatoes will be likely coming earlier and which will be later in the grand scheme that is my garden. And I take it kind of like I take the weather forecast: besides baseball batting averages, the only folks that can be wrong SO often and still keep a job are those that predict the weather--and when I'll get my first tomato!

It's really for comparative purposes only, to compare varieties to each other, but it's officially from transplant time to first ripe tomato. It's usually based on a transplant that has been grown 5 to 7 (or 6 to 8) weeks prior to transplanting... say... a transplant about 8" tall or so. That's why with so many variables (age, size, weather) the DTM is rather useless except to show one variety ripens sooner than another. I just harvested a few Sungold and Galina's that were planted the first week of June... they were started from seed the first week or two of April but spent about 7-8 weeks growing under fluorescent lights and a small greenhouse the latter part of May before they were transplanted in June...

When I was supplying cherry tomatoes to restaurants some years back I came to think a bit like the "Early Bird" and sought out a super early variety. After a few experiments I found one that filled the bill, and it should still be available today. There is a small, determinate, extremely early cherry tomato variety that produces 5/8" to 3/4" yellow fruit. Decent taste, not overly productive but when growing you plant lots of plants to poop up yield- for example in rows 2' apart with spacing at 12 to 14" in the rows. I did use short stakes and a weave between stakes to keep the plants off the ground. The variety is called Chello. It will yield at least a week earlier than Matina. You must expect, however, that the plants will yield in a flush then wither and die--they seem to have little if any desease resistance, or perhaps an early demise is just part of their nature. But by the time they went I had several other good varieties putting out a good yield on long lifed plants. This experience gained in the west central part of PA, zone 6, grimley referred to here as the blight belt.

Okay, so it sounds like you aren't so much worried about the germination itself, but your short growing season, or at least "short" in terms of appropriate tomato-growing weather. So you think you'll do better buying plants that have been started early and grown in greenhouses and which are further along to begin with at planting out time, right? Seems like a valid concern. Again, I think if I were you, I'd sow some tomato seeds, and buy plants. Experiment, but cover your bases, lol. Plant out your winter-sown plants and see how they do, and have your purchased, further-along plants going too, because in all honesty, God forbid any of us is without homegrown tomatoes! I completely understand your concern on that point! :) As I said, my zone is very different, but we do deal with cold springs here, and don't usually plant out tomato seedlings till mid-June or so. And again, my winter-sown tomatoes catch up suprisingly quickly to greenhouse-grown seedlings (I am always surprised by that - don't know why I am, since it happens every spring!) One thing I do when I plant mine out is to use the tops of clear, plastic, 2-liter soda bottles, like little cloches, over each tomato seedling, to give it a bit of protection and added heat. Some people use row cover for added heat, or even low tunnels. Can you do something like that to promote growth?