Diane,

If you choose to start squash and cucumbers indoors I wouldn't recommend more than, at most, a three week head start. They grow so quickly and are not the easiest to transplant. If you do start them indoors they will need the same intensity lighting as your tomato plants. Your greenhouse conditions sound very good.

Remember, if you start anything indoors, under lights, or under glass, it will have to be hardened off to UV light, or else it will burn, and probably die, when you put it out. I suspect, if you have a greenhouse you know all about this : )

I'm personally contemplating starting just one such vine crop (and at that, just one plant) under lights, just to try to get a week or two head start on the harvest. But, as a rule, I don't mess with this, since it takes up space and time, and these crops grow so quickly when direct seeded.

Our last frost date is April 15. I'm just now thinking of starting something indoors like a watermelon or a squash. So my recommendation to you is to count back about 2 1/2 weeks, three at most, and start your seeds.

George
Tahlequah, OK

I wouldn't even mess with starting squash or cucumber seeds indoors or in greenhouse....especially cucumbers. They are fast growing...only takes about 65 days to produce the fruit.
As for squash they really don't like to have their roots disturbed and sometimes will go into shock when transplanted...which will set back plant or even kill it sometimes.
We plant over 1000 hills of pumpkins and squash each year usually in May and have had complete success planting seeds in ground. We plant cucumbers in late May and have cucumbers by late July/early August.
If you want seeds to grow faster use organic fertilizer....like seaweed/kelp mixture and your plants will take off really quickly.

Good luck!!

I started mini white cucumber inside and they all died when I transplanted and put them outside. I'm going to direct sow them along with my squash this weekend...