Amber sent in this question which I answer below.
Q: This will be my second year with my ko roses. The problem I’ve been having is they are all scragly, only growth mainly at the top of the branches. I pruned them a little during the growing season but they didn’t fill in.They were repeat bloomers and are still producing. I want a prettier fuller bush. What can I do to make this happen? ( Panama City Fl.)
A: The loss of leaves on the lower part of the knock out rose is more than likely caused by a fungal leaf disease like black spot.
Though knock out roses are supposed to be disease resistant, mine still succumb to some black spot due to the hot, humid summers in my area. With black spot, the plant’s older lower leaves are affected at first, getting black spots on them, then yellowing, then falling off the plant.
So you end up with a scraggly knock out rose plant with growth on the top half of the plant and not much on the bottom half. In hot, humid areas, you can’t get rid of black spot completely but you can manage it with good garden hygiene and a regular spray program which is discussed in this article on black spot.
If black spot isn’t affecting your knock out roses and you want “prettier, fuller rose bushes” be sure to give them a good annual prune as discussed in this article on pruning knock out roses, (best time for this in your area is February) and be sure to feed them regularly during the growing season; every 6 weeks from early spring to mid autumn in warm areas like yours.