Planting under maple trees can be a challenge
Question: I have dry shade under maple trees. What can I plant there?
Answer: There is no question that this is one of the important problems of modern landscapes. We have a problem of very little light and, because of usually very nice foliage, an impenetrable crown and thus no water. Maples are notoriously surface rooted, and with a thick mass of leaves, they transpire water at a great rate, using up what little water is available.
To solve this problem, I'm going to be brutal: You can cut down the tree and plant another species; or plant another species of maple -- heaven knows there are hundreds of them. Some forms have ascending branching or vase shapes that allow a lot more light and a much smaller crown, making it possible to thin the branches of the crown to allow more light, but I personally do not like to see any tree with a perfect open-grown crown handled in this way. It is usually the beginning of the end.
You could trim up some of the lower branches and install a soaker hose or even a sprinkler arrangement to facilitate growth of a much wider range under a big old tree. I know for a fact that Baltic ivy will work, and after mulching at planting time and watering it until it is established, it is sustainable. My mother had to deal with such a tree near her herb garden and found that Sweet woodruff worked very charmingly.
Also, coming up early to bloom in February were several species of Hellebore. One good reference book is "Hellebores, A Comprehensive Guide," by C. Colston Burrell and Judith Knott Tyler. Tyler spoke at the garden symposium this spring at Chatham University, and shared her experience of underplanting a whole forest (as far as three hoses could reach) of maple shade. Another of her successful plant groups was hosta. Here you can experiment forever until you will find a cultivar of pleasing color, correct height, density and even an exciting flowering personality.
Other options are primroses and coral bells -- both are stalwart survivors in dense shade. You can see examples of both at Martha and Charles Oliver's Primrose Path Nursery, in Scottdale. My next choice would be a collection of astible. To see it growing successfully, visit the outside garden at Phipps Conservatory. However, after this plant finishes blooming and if it is not watered, it can become unkempt.
Although it is almost impossible to mow under a maple tree because of surface roots, if the tree has already been trimmed up to allow light, you could try planting Poa trivialis, a woodland-occurring bluegrass that is usually the only grass species you will find covering the sunny spots in tall forests. This is even better than fescue grass, which is recommended for shady lawns. Lift the mower blade to 4 inches.
And finally, you can allow the branches on many trees (like beech, crabapples and weeping species) to come completely to the ground. Shrubs, especially the evergreen shrubs, will keep all weedy growth out and are dense enough that no one can see under the tree or shrub. Therefore, a nice edge and mulch one-foot beyond the foliage looks great. Just last week, I almost stopped along the road to keep a homeowner from trimming a "cripsii" (golden) falsecypress. Not only had he trimmed off all of the gold but also had allowed the light for weeds to grow where they are difficult to pull.