So... did I cook my seeds?

I'm living in a camper van on vacant land I'm developing, so keeping my seed trays indoors in temperature-controlled conditions is not an option at the moment. Indoor space of any type is at a premium, so I left my seed trays outside, figuring it'd be less than optimal but the seeds should still germinate eventually, right?

I left the covers on so I don't have to water them multiple times a day, but I didn't realize quite how hot it would get in there with the greenhouse effect. I had some seeds in wet paper towel in there, thinking it'd be nice to keep them a bit warm, but then I checked on them mid-day once and the paper towels were almost painfully hot to touch.

None of the seeds in the trays have germinated, and it's been like three weeks since I planted them. It's a mix of different plants, nothing that's supposed to be particularly slow to germinate. Did I just cook the whole batch?

Related question: is it too late in the season to start over with tomatoes and peppers and whatnot? Should I just save the rest of those seeds for next spring?

Yes, you probably cooked your seeds... think of how hot a compost bin needs to get to sterilize weed seeds. If it was hot to the touch, probably too hot for seeds.  I've fried several seedlings over the years, leaving them outside in full sun with a clear cover on them in an attempt to avoid drying them out.

If it's too late to start over from seeds is completely up to where you live, and when first and last frost is, and what the days to maturity listed on the package is... For me, it would be too late for tomatos and peppers, but plenty of things grow very well direct seeded.

Personally, at least for tomatos, i would go to a garden centre and look for a few cheap six packs of tomatos, or alternatively one large plant, then plant cuttings from it (tomatos root very easily from cuttings).

You may do better next time, trying direct seeding in the ground, or choosing to seed into pots with more soil volume to avoid quick spikes in temp, or even starting your seeds in any part shade (ideally afternoon shade) you can find! Real sunlight is much brighter than most indoor grow lights, so part shade can work very well. A European style seedling bed might work well for you, with a window you can prop open during the day and close at night.

If you are doing the wet paper towel method, you don't usually need light until the seeds germinate. I find on top of my fridge works well, then transplanting the sprouted seeds into trays. It's not ideal, but i've been known to leave trays outside in full sun with standing water at the bottom of them, maybe 1/2", which evaporates over the course of the day and keeps things from drying out.

....knowing how hot things can get through clear plastic or glass it's pretty likely
Can you dig down through the soil and see if you can find any seeds or signs of life?

I just lost a number of peanut seeds started in pots that I let stay too wet and I know I've baked some seeds over the years.

I don't know how long your season is there but I would definitely try a few more anyway.
Here I've planted tomato seeds as late as mid may and gotten nice fall tomatoes but had to water a lot over the summer.

good luck!

I often start flats of things in the shade or even in the house until they've sprouted so they don't dry out so quickly...even lay a piece of cloth on top to dampen if they don't need light to germinate.
Sometimes even after sprouting I leave them in partial shade and try to water from underneath if possible.

Thanks for confirming, I definitely thought they were cooked but didn't want to give up on watering them until I was sure. I did dig up a couple of the larger seeds, they looked just like the day I planted them. They were probably all cooked within the first couple days and I just didn't realize. I'll have another go depending on the days-to-maturity numbers.

And thanks for all the tips on other methods, I've definitely been trying all the methods that make sense for me, and mostly learning all the ways each one can go wrong. Good to know about tomatoes propagating from cuttings, I'll see what I can find locally for that. I've shied away from plants in pots after I had like three or four basil plants immediately bolt and/or die within a couple weeks of being outside. But maybe tomatoes will do better, only one way to find out!