Summer heat can make lettuce bitter. I grow lettuce all summer by covering it with shade cloth. I always try to water it the night before I pick. I always pick in the morning before it gets terribly hot. I also bring it right into the house and put it into very cold water for about 15 minutes to take some of the heat out of it. I then keep it in the refrigerator for about a week, or so. I don't have any trouble with wilting.
I plant and pick lettuce spring, summer and fall. Last year we covered it with a tarp at night and were able to pick it up to Christmas. You might want to plant some more for early fall harvest. I plant a small section about once a month to keep a steady harvest. I like the small leave so nothing ever gets a chance to form any sort of head.

Agree it is the heat and humidity. Lettuces do best in early spring. They just aren't heat-tolerant at all but thrive in chilly temps and will actually tolerate light freezes just fine.

I'm about to plant a new run of Black seeded simpson loose leaf. My head and buttercrunch lettuce bolted in the heat before it even really got bad and I'll have plenty of time to grow more and shall be doing it all through the coming fall.

I planted two more rows of Blk.Seeded Simp. and one of Red Sails, eight indiv. Romaine transplants and four Summertime head lettuce plants all in the second week of July. As of today, all are doing great, the the loose leaf is growing so well I may be able to harvest soon. However, I'm still waiting on ripe tomatoes and cucumbers to complete the salad. Weather-wise, it's been hot and humid; but I water whenever I see the soil very dry or plants looking a bit sad. Also keep the dirt between rows cultivated so that any rain we do get doesn't run right off.

It's true that lettuce does better in cooler weather, and some will bolt at the first sign of hot weather, but there ARE some varieties that are heat tolerant.

You may want to try one of these varieties next summer:

Jericho (Romaine)
Nevada
Revolution
Sierra
Slobolt (Grand Rapids type)
New Red Fire
Simpson Elite

Fedco Seeds offers a special Summer Lettuce Mix that is supposed to be very heat tolerant. I would check there, or Pinetree Garden Seeds, or Territorial Seed Company for the varieties listed above.

I pulled my lettuce a couple of weeks ago, and started seed indoors for a fall crop. Our temps are hovering close to 100, so I'm waiting for it to cool down, at least into the 80's, before planting out my fall crop.

Bonnie

Nevada planted here in May has begun to elongate but has not yet bolted. It holds forever in the garden and just gets bigger and bigger. Nevada has other desirable attributes in addition to bolt reistance. It is a beautiful lettuce. Sierra is a red version of Nevada.

Seeing these on Bonnie's list makes me think her other recommendations are good also.

Jim

Are Black Seeded Simpson or Grand rapids 'loose leaf' type?

What other type of lettuce are there besides loose leaf lettuce?

Black seeded Simpson is a loose leaf, and will do very well in the cool weather. I've had it sail through frosts with only a sheet tossed over it, but of course the ground temp never really gets terribly cold here. As the temperatures warm up it will slowly start to get more and more bitter, and then bolt.

Now this is "book learning," not personal experience  other than loose leaf lettuces there are the "loose head" lettuces like Romaine or Bibb, and the "head" lettuces like iceberg that make really tight heads.

I've only tried leaf lettuce, and mesclun mix (yummy!), but I may try Romaine next year. Pretty much any lettuce will bolt if it gets hot enough, which it does here starting about May. I'm looking forward to planting more lettuce toward the end of September...

I've grown head lettuce successfully but it's very dependent on weather quirks, and even Grand Rapids bolted off the get-go this year and it's supposed to be a slow to bolt variety. I also put in buttercrunch, because it's a nice mid-way lettuce between the head and loose leaf. It didn't fare much better. Had I gotten the garden in early both should have done super, as we had months and months of above freezing, cool days and generous rains. But, it didn't dry out long enough to get a tractor in there until the first of June. Now, it won't rain well, and the ground is too hard to till. LOL. Good fruit year, however. You win some, you lose some.

So far my lettuce in about 35 days old and has not bolted. How long does it take to bolt?

If it does bolt, will taking the flowers off keep it going?

I bragged too soon. Awhile ago I picked leaf lettuce and two plants had already sent up a stalk that called out, "I'm gonna bolt!" I cut those two off, the leaves were still fine and edible but at the end of the stalk there was the milky sap. Not just a little, but the kind you get with bolt. It's appx. 25 - 28 days old; so I'm learning something. Plus, very hot and humid with little rain here. I've been watering them as soon as the soil dries,too.

Will be interested to see how the head lettuce transplant do. As stated before, I planted those at the same time, and outer leaves are starting to fold in upon each other. The Romaine are upright and strong so far.

It was the Black Seeded Simpson that threatened to bolt already, forgot to mention that.

I checked my records and here are the dates for this years crop. Keep in mind, I'm a zone 5, and mine were planted out in cool weather. If you planted them out when it was already hot outside, it's going to bolt much sooner, like Schoolhouse's did.

Wintersowed on 1/30/08
Germinated first week of March
Planted out on 4/26/08
Started harvesting 6/1/08
Pulled the last of it, due to bolting on 7/22/08

Hope this helps,
Bonnie

I'm still harvesting Green Ice from a planting made in May, but our hottest weather so far this year was at the beginning of June, and since then it has rained 6 days out of 7 every week.

I picked a big basket of leaf lettuce from my second planting, put in July, this morning. Again, the Black Seeded Simpson showed signs of bolting (tho early signs) on two plants. But the Red Sails is beautiful in all this hot weather. The Romaine is tall and healthy. The head lettuce continues to form heads. It's been dry here also, so I've been watering whenever the soil demands it; but no overhead watering, I'm putting the watering can spout near the bottom of the plants as I go up and down the rows. I've harvested heavily twice off of three rows of the leaf lettuce and I'm convinced I'll get another maybe a third.

Posted by digdirt 6 -7 AR (My Page) on Sat, Aug 2, 08 at 14:51

Agree it is the heat and humidity. Lettuces do best in early spring. They just aren't heat-tolerant at all but thrive in chilly temps and will actually tolerate light freezes just fine.

*********** REPLY SEPARATOR ***********

Thanks for all replies.

I didn't know they can do OK in cold. Do you think they can go until thanksgiving in zone 6?

Update, 10 days later: Two of the Romaine wanted to send up flower stalks so on Tuesday I snipped the stalks out and picked the outer leaves; then harvested two other plants before they got the same idea and gave them away. Looks like I'll be eating alot of Caesar Salad sooner than I wanted to.

Yesterday, picked another big basket of the leaf, no bolting this time for the Simpson and the Red Sails has not done so yet at all. Head lettuce doing fine, again, so far. Must mention that it's finally raining here yesterday and today!
Temps are cooler because of that.

Planted mix leaf lettuce in the garden on 3-22, All the seedlings are sprouting and are quite crowded. How much thinning is needed with leaf lettuce?

Spacing for leaf lettuce is up to you. If you plan to harvest a few leaves from each plant every week or so, then maybe 3-4 inch space would work. If you want to harvest the entire plant at once, then maybe 6-8" would be best. Micromixes could be sown thickly and then cut all at once several times during the season. I grow several varieties of leaf, and space 4-6".

I am trying to find by experiment what and how to grow lettuce all year round in the swamp!!! the first problem has been the tendency to grow long necks on some varieties (Simpsons and Salad Bowls), although I haven't actually seen anything bolt. the most serious problem is the tendency to turn bitter. (as noted above, this can be cured by several days in the fridge). I do note that Prizeleaf, Loma and Red Galactic do not seem to turn bitter at all. Prizeleaf is worth a trial by everyone - beautiful delicious leaves, fast growing!!!

I will report more at the end of the year, including evaluations of all the varieties I have tried.

Michael
Hampstead, NC

Hmm... I have an AeroGarden, and our Black Seeded Simpson is bitter, too. I don't know why, it might be just the way it grows??? I have a few questions that one of you could answer. Here they are:

One of the stalks of our Black Seeded Simpson has a red stub on top. Is this normal??? Is it a plant disease??? Please let me know ASAP.

Goodbye! 🙋‍♀️