I live in Montana where summer nights often drop into the 50s, but soar into the 90s during the day. I built a small greenhouse for my tomatoes. They grow nice and big, but don't ripen. It's September now, and I have these huge green tomatoes in my greenhouse, but they will not turn red. Please advise.
What are the days to maturity for your specific tomato? Each variety takes a different amount of time to ripen. Even with a greenhouse, you should choose varieties with lower number of days to maturity. They will ripen...even tomatoes picked green will eventually ripen. I'm afraid there isn't much you can do to hasten the process.