You might have a problem with the soil drying too fast.
Can also try stacking on a pot that's half full. Would give added rootspace, but not as tall or as unstable as stacking on a full pot.
Rusty Trichome Reviewed by Rusty Trichome on . Pot Stacking... Ok, apparently either I get too busy, or too lazy. Here's the background... I ran a grow thru to harvest. (Indica dom - 5 gallon pot) After harvest, I flushed well, and trimmed remaining foliage for a re-veg in the same 5 gallon pot. I do this with virtually every grow, picking the finest example of the run, and re-vegging for clones. I re-vegged for about a month, and she was ready for the flower room again. When I switched her (around 6 days ago) I transplanted into a 7 gallon pot. Rating: 5