well, for anyone to be able to help u with this you need to give more info about your grow, like what kind of lights, soil or hydro, how old are your plants, nutes? leaves die for alot of reasons, so its hard to pinpoint exactly what could be wrong with out knowing your setup
my plants r half foot tall
i keep them in my window but gona transfer outside
i water every time the soil feels dry i poke my finger in it and if its dry inside i water