Hi all, I am planning just a few containers for spring. I would like to grow leaf lettuces in pots. My last attempts have been horrible. I grow from seed and many of the small plants get stunted after thinning and when I do get leaves they are very bitter. What am I doing wrong? 
I know this is totally out of left field, but you could try Kratky hydroponics. No water pumps needed. I haven’t done it myself… but will more than likely give it a try some day.
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I have grown hydroponic lettuce in the past, though not using the Kratky method, instead I used a mistponics method. Having said that the big issue with lettuce growth is keeping it in the correct temperature range, as then tend to start to bloom and send up a stalk when temperatures get into the 80’s this is when they turn bitter.
Start early - lettuce is quite frost hardy
Don’t plan to thin, lettuce doesn’t like to be crowded
Keep it well watered with cold water
Fertilize
Choose heat tolerant varieties with a short time to harvest
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Lettuce needs hardly any water when young and then lots once they take off, then only a little again when maturing heads so the plants don’t rot.
I’d try starting some single plants in cell flats and transplant when roots start to crawl out the bottom, the wet/dry cycle seems to be very good for young seedlings.
One other thing that can cause bitterness and stunted growth is N or K deficiency. I grow lettuce all summer here, the plants don’t get as big but as long as they are watered daily during the heat the quality is still good.
Pro-tip: lettuce is bitter because of the sap, harvest early in the morning before it rises, if still too bitter then store in the fridge for a day or 2 and the bitter compounds will be metabolized.
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I definitely haven’t solved my own problem, but I definitely think that letting lettuce struggle is vastly superior than over watering. I think I solved some of my personal problem by putting my lettuce in my greenhouse and forgetting it. Last time I checked it they were the biggest I’d ever managed to get in seed trays.
Growing them under fluorescent lights seemed like it should have resulted in bumper crops but I stunt them out every frigging time.
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Lettuce, as well as brassicas, is most heat-sensitive in the root zone. When hot weather comes, keeping the root zone well watered helps a lot to retard bolting.
A thick mulch would also do this, but that promotes slugs
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How do I get rid of bitterness?
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Once it develops, you don’t really get rid of it
Best to keep succession plantings going and harvest young
As long as it is not waxy and tough already, washing and storing in the fridge should get rid of some of the bitterness. Outer leaves tend to be more bitter, but they also have more calcium and magnesium.
I used to grow the most delicious lettuce that was sweet! If I wanted bitter lettuce I’d grow Frissée! I know Lois or Ant Mary has the answer!
Try SlowBolt lettuce. It is not high quality, but it takes the heat, does not readily bolt and keeps producing. i grow around 18 varieties of lettuce. Paris island is also another one that tends not to get bitter too fast it is a romaine type. Both of these are rougher lettuces and not high quality, but very good given their growing habits.
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Thanks sooo much!
If you e-mail me your address I would be happy to send you a few seeds of paris and slowbolt to try out.
Thanks Imhave them coming. Ordered them last night. 
Two of our favorites! I like red leafs, too.
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The lettuce is still doing well with all the extra moisture this year and abnormal cool weather.
Sometimes when we buy seed some dill or carrots get mixed in with the lettuce seed.
I harvest what i want for supper and feel satisfied when i see it sold for $4 or $5. It took a minutes worth of work. Its not so much about the money as it is nutrition. My health was not the best lately but i intend to get myself as healthy as possible on fresh vegetables and fruits during these times of plenty.
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Looks great!!!
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