Plants that are in greenhouses, under heavy shade cloth, and the such are trying to reach for more sun so they will tend to be taller and skinnier. At least this is what I have observed.
I have noticed this on the daylilies that I don't sell that are in pots that are really close together, they get huge and then there is lots and lots of foliage; they get tall and leggy trying to reach the sun because they are being shaded by their neighbors.
