I recently purchased a few flats of marigolds from a nearby nursery. The tags say they should range in size from 6-24 in, depending on variety. So I planted them in 4 different rows according to claimed height, but they are all growing about the same, the so-called tall varieties aren't any taller than the short ones. Am I doing something wrong? I fertilize on a weekly basis with a bloom enhancing fertilizer. Any suggestion would be appreciated.