my clones are about 6" for the t-5 light its self. I haven't had an issue with roots in the clear cups, which help me see the progress thru the day. I can tell you i am also able to see that the soil is wet from top to bottom, with water drops around the cup. I pop holes on bottom,and sides up to half way up. causes these roots to really spread. i also have a rockwool thats placed in the soil as well. I use b-52 and water 4ml per gal. this is applied as a spray and the feed every time unless i am giving nutrients at which i feed at a 1/4 feed, until i hit transplant.