Planning to germ seeds and put into regular nursery pots that are 6" in diameter and 7" deep. I will leave them in those pots (taking outside in the daytime and bring them in at night) and sometime towards the middle of May I will transplant into 15 gal. SmartPots. Given the size of the nursery pots, how tall can I let the plants get before they "must" go to there permanent home outside ?