Our woodland property is beautiful with many Mature Oaks. As we create areas for planting, we find areas that are very difficult to dig. With many roots and stones, it's even hard to get a shovel in. At times I have been planting above the surface and mounding up with chips or top soil. In the long term will these plantings survive, since they are not down in native soil? Is adding top soil or chips/compost for planting going to work for the longer term?