Question
My wife and I are looking to buy a house that has two Magnolia trees in the front yard. The roots are extremely shallow--taking over the shaded area underneath both trees. As far as we can tell there are two options--cut down the trees (which we don't want to do) or build elevated planting beds, cover the roots with up to 2 feet of dirt and plant other plants/flowers underneath. Do you have any thoughts? My biggest concern is that the roots maybe need to be exposed and covering will kill the tree. Can you help us with this dilemma?

Answer
If you add more than 3 inches of soil over the roots the trees will die. The roots do not need to be exposed so you can put good top soil or sand over the roots but if you use too much the weight of the soil will kill the roots  and then the trees.  Magnolia mainly due to the shade will kill most plants under them (grass etc). You can prune some of the lower limbs which will allow more light to get under the trees. There are plants that will grow under this situation. Here is a web link to one persons experience of growing plants under trees that might give you some idea of which plants to use.

http://wvgardengate.homestead.com/Planting_Under_Trees.htm