My sims are always rolling the 'grow [quality] [type of plant]' want but I can't for the life of me tell what it means. At what point in the plant's life is it considered 'grown?' It doesn't seem to get fulfilled, but I almost always delete it because I can't seem to fulfill it, and it usually rolls right after I have just harvested the very same plant.
In my game I've noticed this type of wish is usually satisfied when the plant reaches maturity. Since I typically plant 2 of each plant what often happens in my game is that one plant will mature, the wish to repeat the feat will roll up, then the second plant will mature a second or two later and satisfy the wish. Like the similar fishing wish, the quality doesn't have to be an exact match, as long as the quality of the plant is equal to or better than the quality requested in the wish (so a perfect tomato plant will satisfy the wish to grow an excellent tomato plant, in much the same way that a perfect anchovy satisfies the wish to catch an excellent anchovy).
Sometimes satisfying this wish will trigger a wish to grow the fruit of the plant - i.e. satisfying the wish to grow a life plant might be followed by a wish to grow a life fruit. This one's easy to satisfy, lock it in and then wait a day or so until the plant fruits.