I have always started them about 5th of May (the ws way) for planting out just on or after the 15th.

Vera

....I should clarify.
That would be melon and pumpkin :D
I don't like zucks but I'm guessing if I were to grow any this would be the appropriate timing for them also.

Thanks for the response. Do you think it would be okay to start them any earlier?

You could but if they get too big it could be tough getting them to transplant well. They CAN stunt growth if they are subjected to too much chilly weather or die even in a protected container if temps drop to freezing. Also I start laying down plastic (black) about a month before I plan to transplant to get the soil nice and warm.

Vera