>For example, sometimes my tomatoes need a little extra magnesium. How do you go about determining this? I just built a 400 sq. ft. greenhouse this year, and a

>For example, sometimes my tomatoes need a little extra magnesium. How do you go about determining this? I just built a 400 sq. ft. greenhouse this year, and aside from watching the plants get bigger each day, I'm not really sure how to tell if I'm "doing it right".