u/Oldalgebra

I have a planting area in my front yard that contains a zillion magnolia tree roots. Most are just below the service. (The City planted magnolia trees in the parking strip many, many, many years ago and their roots have spread looking for water.) I have managed to rid the area of the larger roots, but there's sheet of roots that can only be described as a Root Screen, much like a window screen that lays below the entire area, choking out everything except my low-growing ceanothus. All my yarrow plants seemed to survive for a while, sending out rhizomes. Some even produced rather whimpy blooms. But finally, almost over night, black rot takes over. I've tried not watering. I've tried watering more. Nothing! Can you help me by suggesting plants that might dominate? I'd love some with color, but after three years, I'll put in anything that might have a chance of survival.