I'm similar to Joanne (same city) in that I start my tomatoes indoors, but don't have a greenhouse. I grow almost all my tomatoes in large pots, and very seldom put them into the ground and therefore usually choose fast maturing determinants. The season is so short that only having one flush of blooms isn't an issue. I usually start the seeds in late February.
I tend to move my tomatoes outside and out from under the lights very early--usually when the daytime temperature is around 10C. Even though that is a bit cool for growth, I've found that earlier transition to sunlight helps the plant adjust more easily to natural light and to transplant when the temperatures are warmer. July is about the only month here where the night time temperatures are over 15C, so the objective is to have them fully mature by that time to achieve optimal flowering.
