Agree with Peter that if you have a heat tolerant variety you can very likely get it to germinate now especially if you give it some shade. If not then within a couple of weeks the soil temps should begin to decline enough.

With containers the soil temps fluctuate more so you might need to insulate them from the heat or move them to the shade.

As to how late you can plant? All depends on when your first hard freeze is but you can always cover it if necessary for protection and drag out the season a bit longer that way.

Dave

Thank you both! I wasn't sure if it was too late to start growing outdoors. Good to know that I still have time.

I like to start fall lettuce indoors about now and then transplant to my garden in mid August with some shade protection for a couple weeks. This will give me mature lettuce heads in October.

Check out Johnny's Seeds website for info on planting dates. Your library might also have copies of Eliot Coleman's books on 4 season gardening (in Maine). Some varieties of lettuce are more cold tolerant than others which a catalog/website like Johnny's will explain. I have planted spinach outdoors in the ground late and without any kind of protection, have it start re-growing in the spring. Next spring, don't be too quick to dump containers. Wait to see what starts growing again. Kale is pretty hardy.

I started my fall lettuce and such on July 23rd. They are up now. They need sowed indoors where it is cooler and taken outdoors as soon as they come up.

I grow my leaf lettuce in those window box containers (2 feet long x 6 inch wide). I like them because you can easily move them around. I've done this in the spring only.

If I want to harvest some lettuce and other greens in the fall, can I sow the seeds in those containers, and place them somewhere cool to germinate (the garage for example)? Once they germinate, I would move them outside somewhere shaded. Does this approach make sense?

My concern is that this has been the hottest summer I can remember, with temps well into the 90s. If the heat persists well into August, will I have problems growing these greens?

When seedlings are portable, you can move them out of the heat for part of the day. It is best to plant the fall crop where they get a little bit of shade and WATER WELL.

If I plant under hoop houses, I plant lettuce in September in an open bed. The hoop houses are added in November, and the lettuce is for spring consumption.