I am in downtown Toronto and have a full shade sand/loam site with a 10 year old pagoda dogwood under which I have been planting perennials and ferns since the tree was first planted. There is also a euonymous vine growing up the brick wall directly behind the tree, about four feet from its base. This year, the ferns, brunnera, pulmonaria, have become strangled by the roots of both tree and vine. I’ve dug everything out and am not sure whether to cut away new holes and replant what I have, or plant something else entirely (groundcover?). If I replant the perennials and ferns, will the roots not just go at them again before long? Thanks so much for advice.
Dogwoods tend to have their roots fairly close to the surface, so shallow-rooted, shade-loving perennials, such as pulmonaria, ferns, lamium, foamflower (Tiarella), epimedium, hakonechloa and even sedges such as ‘Ice Dance’ might be good suggestions. Big-root cranesbill (Geranium macrorrhizum) is another great “filler” in shade and seems to grow pretty much anywhere. For spring blooming, corydalis and Virginia bluebells will suit the area if you want to try something new.
Most perennials should be divided after 10 years so it seems right to dig them up divide, clean the roots away and replant them a bit farther out where the soil is not so root-bound. You can fill the area near the dogwood with shallow-rooted perennial groundcovers (stay away from periwinkle and English ivy as they are now considered very invasive).
Another point to consider is light and soil. The tree size may be providing more shade than it did in the past and that in turn could be one of the reasons for decreased plant performance. Also, feeding the soil with compost, and watering regularly is crucial. Invasive roots suck the moisture and nourishment from the soil, so extra care is needed to nurture other plants.
And finally, in answer to your question of “will this happen again” the answer is yes but it can be managed!