We bought an old house with a small urban backyard, consisting of pavers and some areas with slightly raised planting beds (about 6" high), no lawn/exposed soil. The planting beds include hostas; boxwood and euonymus shrubs; and an old yew that has grown about 10 feet high -- all grow very well and are healthy. They are not watered, except by rainfall. I always assumed the planting areas went down to directly to dirt but after poking down with a metal stake in several spots I hit what feels like concrete, just an inch or two below where the adjacent pavers are. This must be a concrete subbase for the pavers.

Is it possible all these shrubs and perennials are growing in 6" or less of soil?? Even a 10 feet high yew?? We were considering adding some trees in these planting areas but that seems an impossible idea now. If we would need to break up the concrete subbase and remove whatever gravel and other layers may be under it, it may become too expensive for us and we would rethink our design. For example, we may add some large planters to hold small trees and/or use a pergola to provide shade and privacy. I prefer to avoid planters for trees because they are bulky and our space is small.

We don't want to dig up the whole area to investigate further and lose all the plantings that are already there now, so I'm hoping we may be able to navigate with some guidance from this group.

Thank you!