We started to take out the mulch around our house to put in rock, when we started to rake away the mulch we noticed a lot of roots at the surface, we could not figure out why. It was not under we took out a bush that we discovered that there was a layer of Styrofoam surrounding the house. The house is built on a slab and when they built it looks like they added another layer of Styrofoam around the round going out about 3 feet for frost protection. So the plants only had about 4 inches of soil before they hit the Styrofoam. So now what do we do? we don't want to remove the Styrofoam as it looks like it is part of the structure and a frost barrier, but I want to be able to plant bushes and have them grow. What our options are?