One plant crowding out, shading out, and so eventually killing it is normal plant behavior. My huge lantana was shading out the white butterfly bush next to it, so I cut back that side of the lantana in hopes the butterfly bush can recover its vigor. Many of the trees I planted after Hurricane Katrina have gotten shaded out and died because of volunteer native trees, making me wonder why I planted them in the first place.
This is normal.

Sherry

Hi Sherry,

I just saw your response now! Thanks for getting back to me and I am sorry that I didn't see your response sooner.

Jolene