I work with a woman who grows greens for market, and she sows and grows continually throughout the summer. The heads are not as big in say, late July and August, but she still manages to grow them.

I would definitely give it a try. I only grow lettuce myself, so I'm not familiar with growing other greens (except spinach which I don't even bother with in the summer), but if you have an area that gets good morning sun and some afternoon shade, the lettuces will probably do a bit better there in the heat of summer (that's what I do). Or try growing them between other vegetable plants or in the shade of a bean or cuke trellis.

I prefer mixed lettuces in my salad, so I grow green leaf, red leaf, romaine, butterheads. My very favorite is New Red Fire, which is a bit difficult to grow but worth it.

You can also just sow in trays and cut as baby lettuces. You should get at least two cuttings per tray, perhaps a third, although the third may be a bit bitter.

I get most of my lettuce seeds from Johnny's. If you go to their site you will want to grow every green known to humankind, lol.

I don't grow them, but my friend who grows for market also grows mustard greens, arugula, kale, chard, and tatsoi and pak choi (sp??), escarole, and others throughout the summer. And I should mention that all of them, plus her lettuce, is grown at a farm that get absolutely full, hot sun all day. So it can be done!

Good luck!
Dee

Here is a link that might be useful: Johnny's

In the summer I grow my lettuce on the shady side of my tomato plants (I grow basil on the sunny side). I had good luck with Swiss chard last year - I think the variety was neon brights or rainbow brights. In fact I still have a couple ziplock bags full of chard in my freezer.

Spinach and lettuce both tend to bolt in the heat. I know people who plant small crops every 2 weeks to help deal with that.

I agree with recommendation for Johnny's seeds. Their website contains some growing information so you can see what varieties are best for cool spring or warm summer. I have had very good luck with Tyee spinach planted in early April but also in late August. Last winter, without any cover at all and little snow, the spinach wintered over. When it started growing again in the early spring I was able to pick outer leaves. Right now, near the end of May (here in NH) it's huge but shows some signs of getting ready to bolt. (so I'm glad we've got some cool rain right now)
On Johnny's you can also see which lettuce varieties can withstand summer temps.

Somewhere I read that spinach is day length sensitive not just heat sensitive.

Due to weather and little time, my early plantings are not doing well. I'm going to try putting some greens in a bed that gets only part sun. I still have to remind myself to give newly sown beds a good watering and to keep them watered.

New zealand spinach is made to withstand heat is slow to bolt. I had swiss chard all summer last year. It really is good and the bright lights is very pretty.