Serious gardeners in New England, especially food-gardeners, build coldframes to extend the growing season. Properly done, you can add at least a month to the growing season for some things.
I used to mess with things like that, but I don't bother anymore. If I lived in Maine, though, I'd definitely have a coldframe full of spinach, leaf lettuces, etc.
I've even tried putting tomatoes out in late April here, but it never works out. Milk jugs, polyurethane, etc. Big hassle. Fact is, around here, if you put them out in late May they quickly catch up to the early birds, and even exceed them because they have endured no cool weather stresses. Tomatoes do not really put on growth without warm nights - above 55 F. We are still in the 30s on some nights.
If you have money to burn, the best thing is a good-sized real greenhouse. I would attach one to the house, with interior and exterior doors, so you could just open the door and let the rich earthy and flower and herb and plant smells infuse the house. Home-grown Beefsteak tomatoes 12 months/year.
Pic is Beefsteaks, the only tomato I truly enjoy eating, especially when hot from the sun. We usually only get a few weeks of them ripening, mid-late August-early September. Is it worth the trouble? For me, it is. It is especially pleasant when you can find a big ripe one that a squirrel or chipmunk has not taken a bite out of.
