i grow my seedlings in a red solo cup with many holes in it , when i feel they are close to be root bound in the cups i move them to their final cloth 20 gallon pots in a t.l.o. soil and 25 % worm castings , i never go through with all this up potting thing , with 20 gallon pots its plenty big enough for my root systems to be well over 12 inches wide and i top my plants also and they finish at 4-5 ft tall and 8-10 zips of dried finished bud , they don't get up potted by mother nature outside , i have grown in 30 gallon pots and it worked great also , they were just a bitch to lift so i went back to 20 gallon pots , just plant in a 20 gallon pots and save the up potting grief and the cost of extra pots , i am using mother natures approach to how a plant grows outdoors and the KISS approach. why make more work - cost than you have too .