It never used to be a thing, I'm sure, but in recent years the mini-cos lettuce (like Little Gem) that I've grown have quickly gone bitter in the summertime. So much so that I gave up growing them altogether in favour of salad bowl types. I miss the crunch, however, so I'm hoping I've missed something obvious which a wiser head can point out. Growing in partial shade alongside a row of peas, perhaps?