I heard the other day that if your lettuce are bolting to seed quicker than you'd like then the soil might be deficient in MgSO4 better know as Magnesium sulfate or (MgSO4·7H2O), commonly called Epsom salt.
A tablespoon in a watering can of water should fix the problem, so tis said. I will be experimenting but it is something commonly lacking in volcanic soils like I have.
