I found that Nevada was not much more heat tolerant than most other lettuces. It may be a little later to bolt but bolt it will. It did seem to not turn bitter as fast when the weather heats up. Muir actually performs better in the late spring heat IME.

As Dan said, germination in warm soil may pose a problem. You can try sowing indoors under lights and grow out for a couple weeks, harden off, and transplant.

there are some places mention it is a spring/summer lettuce that resist bolting.

i started a 6 pot tray, each with 3 seeds, not a single seed
germinated because i made a mistake to leave the tray where it got some
sun, started a new batch with better germination in cooler spot.. so, i will say that it's definitely true that they won't germinate above 75F. i have a couple trays that i started about 2 weeks ago, the ones on the right is the Nevada (smaller than the rest because i started them later due to the mistake mentioned above)..

they're doing good so far and getting a lot of direct sun.. over 10 hours per day.
going to put some of the bigger ones in the ground this weekend, probably will post an update in a week or so.

I just pulled out my "Devil's Tongue" (a red Deer's Tongue) because it bolted. The stuff I grew over the winter lasted from October until May, this batch lasted from April until the last week of June.

The problem is that it does NOT want to germinate in warm soil and that's all I have.

Even the warmth-tolerant varieties won't germinate with soil temps in the 70s.

When I was selling salad greens and had to start (summer variety) lettuces in summer, I rigged up shade and watered twice daily. Always worked.

> The problem is that it does NOT want to germinate in warm soil and that's all I have.

you have to be creative i suppose. find the coolest area of the house.. obviously 70ish or lower. typically basements (at least mine) have cooler temps.

or maybe try putting them in the warmest part of your refrigerator.
or even putting them in a cooler with a couple ice chucks.
or turn on AC in a room and leave them in there for a few days. lettuce sprouts within 2-3 days.

Pretty interesting. No lettuce germinates at higher temperatures, and it's not because the seeds are just more comfortable when it's cooler. Lettuce has a genome that, at higher temperatures, produces an enzyme that drives production of abscisic acid, which is an effective germination inhibitor. It's called thermo-inhibition. Lettuce probably evolved that way, because high temperatures used to mean that water was scarce, and lettuce would not survive. Of course now, farmers are quite happy to keep the soil for lettuce moist, even when it's hot. So that evolved trait is not constructive for farming. and efforts are underway to breed that trait out. I hear that may be successful in a few years, and we can look forward to real summer lettuce.

Commercial producers in warm climates germinate indoors and plant out, and I understand some farmers who direct seed actually chill the irrigation water!

I should add that if you take the tray with lettuce seeds in soil, and float that tray in a water bath that has a few ice cubes added, the soil temperature will drop significantly, and that may be a convenient way to promote germination.

That's the whole point of rigging up shade and watering--cools the soil.

black simpson isn't doing too well which i kind of expected.. seems to start wilting in afternoon sun/temp after around 85F. Nevada lettuce is doing slightly better, but its still young and too early to tell.

blue dwarf kale that i have seems to be doing exceptionally well.