Creating a Raised Bed Under Tree

I want to create raised beds for planting flowers around the base of several trees. How much soil should I add?

Do not place additional soil around the base of your trees. As little as an inch of soil can kill some trees. The damage caused by changing the soil level will not appear for five or more years. Suffering trees will eventually start to decline. The new growth will be stunted, leaves color up early in the fall, and the tree eventually dies five or ten years later. A better solution is to use organic mulches or plant perennial flowers and groundcovers in the existing soil.