not usually... but in combination with ferts... if they get too dry they cant use them and sometimes theyll show a lil nute burn as a result...
did you see my watering post? (last page)
@RIP: since i started bubbled water... i dont have to have holes in my containers..., i can water extensively and they use it up... enough oxygen present i think... used to get flooded if i did that befoire bubbled water...
@newautofan... use 1tsp h202 (3% cheap grade pharmacy) per gallon of water... bet you'll notice a vigor diofference...
or... bubble your water:
http://www.autoflower.org/videos/52/my-bubbler-diy.html