If you let your seedlings germinate in rockwool, and plant the rw seedling in a plastic red party cup when roots are coming out the bottom. This way you can bury the rockwool cube deep in the cup, so the tiny little stalk is covered with dirt. This will allow your stalk to buff up and get you a crazy root system in that cup. You can just turn the cups upside down to transplant. You dont have to do that, but my girls come out way strong with mad thick stalks.