Why is my garden lettuce bitter,even after a good washing?

Question

Why is my garden lettuce bitter,even after a good washing?

Answer 1

Cool-weather vegetables like lettuce and spinach will grow bitter if left too long in the garden.  They should be harvested before the flower stalk bolts, as once the plant starts growing seed, all its energy is concentrated on the seed development and not leaf development.

Check your seed packet to see how long the growth of your lettuce is. If you left it in the garden too long, you've let it overripe.

Answer 2

too much sun, try to shade them from the afternoon sun.  Also pick them sooner.