Lettuce does not like hot, humid weather. Especially problematic is the fact that it doesn't cool off at night. All you can do is do your best to keep it watered and fertilized.

But, I don't want to say that "stunted" is necessarily what it does. Really, it grows fast in hot weather, but it tends to bolt to seed and is usually so bitter you can't eat it.

To me, "stunted" seems to imply either not enough water or not enough fertility in the soil. I would make sure both are correct -- you really probably couldn't overwater lettuce in this weather except maybe in very heavy clay soil. And, it likes lots of N-P-K.

You could try rigging some shade cloth over some of the plants to see if it helps. Recommended type is knitted 40% black.

You can try Ben Shamen or Jericho which have been bred for hot weather. I also grow in areas that get protection from afternoon sun which seems to help. Many of the oak leaf and romaine types are slow to bolt in hot weather. I know you said yours were stunted. Make sure the plants get lots and lots of water and it helps to mulch around them with some newspaper down and then some straw on top of that.

Lettuce and hot weather don't go together - even hear in zone 3, when temperatures get into the 80s in July, lettuce growth is slow and plants often bolt very prematurely. Beyond that, another factor that can stunt lettuce pretty quick is soil that's too acidic. Make sure your ph is 6.5 or higher.

Water them in the heat of the day to keep the roots cool. This also helps with broccoli.

it really is to bad you all have it so wrong.
the secret to growing lettuce in temps over 75f and to prevent bolting is very simple.
In 1995, USDA lettuce breeder William Waycott, Ph.D., demonstrated that lettuce grown in steady 90 Farenheit temperatures matured without bolting so long as there were only eight hours of daylight. Once exposed to longer daylight hours, the plants' biological docks turned on the mechanism to begin the process to produce seeds.

It really is too bad you fail to understand that bolting is only one of the issues with growing lettuce in the heat. Slowed growth and an often more bitter taste to the leaves are also issues as are getting them to germinate in the first place.

At least you helped the original poster.. oh wait...

Thanks for ALL the feedback!

wulfe all issues you listed are all related to the light and heat issue. by restrict light to 8 hours you can grow none bitter lettuce in temps over 90 degrees.

Lacysue - do you actually cover your lettuce plants up and uncover them every day? or do you just mean direct sun.

Up here it is light from 5:30 AM to 9:00PM this time of year thats 16 hours.

I think she means direct light.

The lettuce I have growing right now gets about 5 hours a day of direct sun .. and growth rate wise and taste wise doesn't compare to the stuff I sowed in early May (same varieties).

The Devil is in the details..8 hours of daylight or 8 hours direct sun? if it's day light then unless you cover your lettuce with a tarp you get bolting in August..As we all know Day light drops off as we get later in the year...

My experience (see my post today) is that the lettuce gets bitter in the hot weather, period...my lettuce bed only gets about 4hours of sun a day and the lettuce did bolt and get bitter.. It occurs to me that it could be you need to replant the lettuce after say three weeks of harvesting simply because the plants are maturing.. (looseleaf lettuce you don't pull the plant but rather harvest snip some leaves).

We have a test case..I just planted two large beds with several varieties yesterday..I'll report back in a few weeks. Will it germinate? Bolt? Or be ok?

The poster that spoke of growing lettuce in 8 hours of light meant 8 hours of ANY light, in all likelyhood.

Plants which are daylength sensitive can respond to light levels of one footcandle, which is almost absolute darkness.

Commercial growers of crops like poinsettias, potted mums, kalanchoes and other short day crops have elaborate blackout systems for their greenhouses to make this possible. Where I used to work, it was an automated system of 100% shade cloth on wiring and controlled with a timer that opened and closed it at the correct time -- 6:00 pm to close, 8:00 am to open -- this was for mums and poinsettias.

The rule is for every day you miss pulling the shade, the plants daylength response is delayed 3 days.

With lettuce, if you wanted to do this, you would have to get a black box or thick black cloth to pull over the plants every day at the right time. Easy to do, but a lot of work. If you forget, it would no doubt get bitter and bolt.