Thanks Ricalynn,
I'll test out the quality thing tomorrow. I need to grow some exceptional steak plants, so I'll set try growing some with "talk to" and see how long they take to become perfect. Then I'll plant some more and grow them for the same length of time with no "talk to" just to see if they develop more slowly.
Edit, I won't be bothering with doing the second part of the test. My steak went from nice to perfect so quickly with "talk to" that the effect was obvious. I planted the steak which was from the shop - nice quality - and used talk and sunshine in the gardening station. On the next day I harvested 4 outstanding steaks and then they were all perfect. So, talking to works until the plants are perfect, then there is no point, so long as you keep one perfect sample of each plant for replanting.