I live west of Loveland CO at 5000 ft. (zone 5) and have been growing melons for ~10 years. At first, I had trouble getting melons ripe here in time. I was about to give up. Then a neighbor had a “melons for sale sign” in early September. They were delicious and let me know it was possible.
Since then I’ve had lots of yummy melons. Varieties I’ve had luck with: Sweet Dakota Rose (watermelon), Lily (Crenshaw), Ha Ogen, Charentais, EarliDew (honeydew).
Things that help- pick shorter season varieties (80 days if possible), start in biodegradable pots indoors in early May, set out in late May/early June, often in Walls of Water, getting soil warm early in the season (black plastic with slits so I can remove once plants get going), keeping disease pressure low during peak hot weather (July and early August), picking off cucumber beetles and discouraging voles, drip irrigation to reduce powdery mildew occurrence, trellised on cattle panels, and protecting against Sept frosts with row cover at night.
As with much of gardening, it’s not one thing, but getting everything to work out for a crop. If something goes wrong, it often means no ripe melons since it is always a race with our short season.
I am always worried when melons are golfball sized in mid July, but they grow fast in August. By late August, days shorten, and they stop getting bigger, but still are ripening.
Figuring out ripeness varies by variety- some “slip” like Honeydew, but others are ripe without slipping.
By late September, the plants usually look pretty beat (I cut back on water then to promote ripening and sweetness, and we have often had a frost by then), but the fruit is wonderful. So much better than I can get at grocery of farmers market.
From three 3X6 trellised beds I got approximately 30 melons.
This season, I am going to try some Lofthouse Oliverson landrace seeds that I bought from Buffalo Seed Co.
I hope this thread gets renewed attention from other Colorado melon lovers. I can always learn more from others’ experiences.