Bigger the root ball the bigger the buds , I use 3 gallon pots but I feed them 4 times a day ,if your growing in soil the smallest I would use it a 7 gallon ,(They hold 5 gallons) ,if your growing photos the minumum I would use is 5 gallon same with autos ,if your growing in dirt you can get away with a 3 gallon if you can water/feed them many times a day