Answer: Surface roots are a natural pattern of growth for certain trees. Covering the trunk and/or roots with a deep layer of soil or deep pile of mulch is harmful to the tree and could eventually kill it by damaging the trunk and main roots. I really would not recommend making this raised bed. Instead, you might consider using a groundcover in that area, perhaps Vinca minor or your hostas. Use compost to amend the soil in individual planting holes for the starter plants and mulch the soil between them without covering the roots. Eventually the vinca (or hosta if you use a spreading variety) should fill in and cover the area. Avoid damaging large roots when you plant. Good luck with your project.
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