What will grow under Norway maples?
Here is the range of responses to this question ranging from nothing to quite a selection. The low light, dry soil, surface roots and the seedlings present a challenge. (Limbing up (removing lower branches) and planting away from the trunk will improve your choices. (Ed.)
Nothing seems to grow under a mature Norway Maple. I would cut it down, buy a new tree and start from scratch. I hate to be so negative but I've had to do it.
It is dry in the shade of just about any maple, but Norway Maples in particular cast very dense shade. You might be able to get something to grow under there, but it will be a real challenge finding plants that can take the lack of moisture and light.
My grass does grow quite well under it
We have Elephant Ear, Caladium, Coleus, Impatiens, Azaleas and Lilies growing under our Norway Maple The Azaleas and spring bulbs have bloomed before the tree leafs out completely and the others grow wonderfully in the moist/shady conditions provided by the dense canopy. (Moist shade? Ed.)
Epimediums are an excellent choice for dry shade.
I started a shade garden under 30 year old maple about 4 years ago. The farther from the base of the tree, the more will grow and the more lush the plants. What has grown best for me, Hosta and Christmas fern. For spring flowers hardy Geraniums "Karmina" and "Biokovo". I planted them last year and they not only tripled in size but bloomed profusely. Stay away from most Astilbe, they need moisture. They may "exist" but will not perform. I have had luck with one variety, though, A. Chinensis. It is dwarf, blooms in August, and has spread into a nice ground cover. Toad lilies for fall. I really love them. You may want to give Plumbago larpentae (Certostigma plumbaginoides) a try. It is now in bloom at the base of the tree.
Don't plant too close, and plant so you'll get some sun. But you'll always have to pull up gazillions of unwanted seedlings every spring, And you'll always have to remove the leaves in the spring, since maple leaves compact and plants can't grow through them.
I have had luck with Iris, Lamium, specimen grasses (Miscanthus), Columbines, Penstemmon, Sedums, Pansies, Violas, and Geraniums (Johnsons blue and natives) in dry shade. I also only set out small plants that do not require me to dig deep holes.
I grow Daffodils and Bluebells under maples and also find that Azaleas and Camellias do well as flowering shrubs. My Hellebores also love living in the mulch. My neighbor has success with Japanese anemonies, also known as windflowers
Pulmanaria does well for me under dense lilacs
Thalictrum does great under dry shade. My Toad Lily needs a lot of moisture
Sweet Williams are growing wonderfully under my Maple...as are Daffodils, Hyacinth's (including the little Grape Hyacinth), Solomons Seal, Day Lily, Widows Tears (or Trinity Plant), Shasta Daises, Astilbe, Hostas (Sum and Substance), Coreopsis (Sunray), Creeping Phlox too.
Another strong plant that tolerates these conditions is Lamiastrum 'Herman's Pride' (the one that is NOT invasive)--beautiful silvery green foliage and pretty yellow flowers in spring But Dicentra (wild and common) do fine, as do Toad Lilies, Solomons Seal, Filipendula, several ornamental grasses, of course ferns, Heuchera, Aconitum (Monkshood), Epimediums, Yews, Pieris andromeda, Kalmia (Mountain Laurel), shade-loving vines.