I grow lettuce much of the year in zone 7. Try growing in the partial shade and keeping them well watered (especially when starting seeds). I generally have about 50% germination in the summer months with heirloom seeds.

Winter Density is my favorite "year round" lettuce variety.

Personally, I never start anything indoors these days. I look for varieties that I can direct seed and still get a crop. Lazy gal :D.

Just planted (direct saw) my lettuce mesclun mix , arugula, raddishes and turnips. Hoping for success. I planted them in a bed which is behind the bed where peppers, eggplants and tomatoes are so I hope they get just enough shade.

Planting this weekend! Can't wait. I am craving greens and brassicas. I will plant both seeds and a few transplants. Still getting peppers, melons and eggplant. I cannot wait for lettuce. I find the red looseleaf varieties do really well here, as does Paris Island Cos.

Here is a link that might be useful: Cowlick Cottage Farm

They say that shade cloth effectively lowers the temperature by 10 degrees. I eeked out a couple extra weeks of lettuce in the early summer by tenting the plants. You just make a canopy, don't bring the cloth to the ground -- that would raise temps.

This fall, I started some from seed and bought some starts as well. The starts were planted under some tomatoes and under some shade cloth. The ones under the 'maters are about twice a big, so I'd guess that serious shade is the optimum condition.

That said, the plants I started from seed are in full sun and growing like gangbusters. I have not had great luck with lettuce from seed in the Spring. (i know i know) But this Fall-planted crop is doing incredibly well.

A very large tree came down in my rear garden last year, finally giving me a place to grow veggies among my flowers. This is the first year I have had any success with growing lettuce and the tips about temperature are very helpful.

Here is a link that might be useful: Diane Cox

I started about a million lettuce seedlings that I got from Gourmet Seed on incredible sale - like 5oz each of Ciucca, Verde Riccolina, Flame, and Bentley - lots of red, about half loose and half headed. I also transplanted some seedlings from my starter shade bed of Parris Island Cos and Black Seeded Simpson.

I just set out the largest Parris Islands and Simpsons in my lettuce house - a quick-hoops hoophouse with 2 mil plastic over it, about 50 sq. feet. It's half full now, and I'm waiting for some of the Ciucca and Flame to finish potting up, and I've got about a million more seeds starting in spread sow planters, plugs, and potted up. I'll have so much left over seed even after direct sowing that I'll probably be using this stuff until it just stops germinating!

I plan to add chard, cabbages, spinach, and roquette to my fall growing leafies.