Browning of leaves, dead plants. Do I cut. He whole leaf off or just the brown/ black leaves? Is there a type of fertilizer to encourage the spiderworts growth. I usually use bloom buster, but it doesn't seem to help them much.
How is the watering? This sounds almost like either too much water or lack of water.
You can remove any dead plant material.
After blooming I actually cut my entire plants down to about 4 to 6 inches from the soil surface.
Here is a link to refresh you on the care requirements.