I didn't know about the tendril test. For me, they just give slightly at the stem end, and the smell is powerful. Of course, the color should have changed entirely to tan. Don't wait too long. They can more fully ripen once picked and sitting indoors for a few days.

I can't grow them here but when I buy them in France I go by the smell and a little pressure with the thumb at the stem end. See above.

Well, they're still green. They got a late start due to the cold, wet weather we had, even into June. No watermelon yet, either. Hope I get something before the shorter days and cooler temps put a stop to things (and that's already started here -- I just came back in the house to put on a sweatshirt - in August!)

Can you cover them in some way? Cloches?

Melons like hot weather, and may just be inappropriate where you live. You may be just outta luck. Sugars won't develop in cool weather.

^^ Yes, I'm aware of that. However, shorter-season melons can and do perform beautifully here. I had fantastic melons last summer - had so many Crenshaw I didn't know what to do with them besides give them and the extra watermelon away. It's just one of those wonky seasons this year.

Cloches are a good idea, but these are on a trellis so that won't work, unfortunately.

Cloches will prevent frost, but won't do much for making real heat. They pretty much tie your air temperature to the soil temperature. Now, if your soil temp is 90F (as mine is now), they might help!

Ooh Ooh! Went outside a short bit ago to do some harvesting and what did I see? A beautifully ripe Charantais! It was delicious. Generous person that I am, I left the other half for DH... LOL! Hopefully I'll get at least a couple more; the rest are still green. Definitely on the to-grow list for next year -- variety is Alvaro. (never tasted a Charantais before, so entirely new to me)

The soil can get really hot under cloches.