Hi! I have a question about the growth habits of wallflowers.

We planted four in our new front bed last year in about May, and they did really well and stayed green over this winter, which was surprising. Before planting we mixed bagged topsoil into our lousy clay soil (house is about 8 years old and it has "new subdividion soil). I also added some slow-release osmocote pellets to the planting holes.

Since then we really haven't done anything, except watering when there were long hot dry stretches last summer. The wallflowers are starting to bloom again, but the plant habit has gotten really unattractive to my eyes-- there's a dead area donut (that started at least by winter), though it's more obvious and ugly for some of the wallflowers. See the picture for an example (and for growth context, the original plants were in quart containers and were about the size of the center green section).

Is this the typical appearance for these plants, or will it fill in eventually? I love the bright yellow flowers (perfect for our house colors), but the growth habit is so unattractive as to completely ruin the appearance of this plant for me. The creeping phlox toward the front of the bed (on the left of the picture) has a much more attractive growth habit, though it grew less prodigiously.

Any advice? Did I do something wrong that I can fix to make these plants grow in more attractively?

Thank you very much for your assistance!