I use 4" cubes because the tray I use is only about 4" deep and aprox 14" wide and 30" long, just basically a stability factor since I dont want them to fall over. the 4" cubes come with a 1" round hole that the 1" cube fits right into. when I see roots from 1" they go into 4". I might just stay with 1" only once I get my 12 pot system running but lots of work in basement b4 that happens lol