Have garden bed in semi-shade, backed up by Pyracantha Firethorn (30-40 years old). Put down weed suppressant & slate mulch 2 years ago and now almost all of my new shade-tolerant plants are dead (except Phormium). Is the mulch preventing proper drainage and not allowing the plants to grow? The soil is heavy/clay and never gets dry. I have spent a fortune on mulch/plants and am now completely frustrated!
You will have to either take away the mulch or put in plants that can take some dampness in the soil, such as hostas, hellebores and astilbes.