The roots grow to where the oxygen is oddly enough and not the light. It is interesting the tap root went to the side and did not grow to the bottom of the pot. Do you have a cold floor or somthing or trim the tap root to grow more stout. I would some times take a clone out of the tray and put it in a 8oz cup to veg. When I put in a one gallon to flower I would trim the roots on the bottom hoping they would grow thicker thru the soil. Dont know if it really kept the plants shorter as I supercropped them but it is somthing to try.

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c