Hi UVG - I have very similar problems although perhaps not as steep of a slope. Does your fence contribute to heat up the area due to reflected western light? My fence is open, but it still gets blazing hot over there and maples and bittersweet compete with the whole bed. I have planted and removed numerous things that did not appreciate that area! Things that have worked include: hostas (varieties that don't burn easily), lady's mantle, lamium, geraniums (look at "Elke" which is supposed to very vigorous in all kinds of conditions and is a groundcover type), columbine, polemonium, monkshood, japanese anemone. Also, take a look at High Country Gardens for ideas, they have decent info on cultural needs. I have tons of tulips in that area that do really well because they bloom before the maples leaf out and they like it dry. As for shrubs, you could try witch hazel. I'm new to shrubs at this point, but I'm trying oakleaf hydrangea in that area (although that is huge, and I can't vouch for it liking the area yet!) There are some really pretty small hydrangeas out that are named after European cities: "Paris" "Venice" etc. Maybe someone could also chime in with ideas for vines to climb on your fence. I recently read that clematis really need constant moisture so that's probably not what you would want to go for, although I have a sweet autumn clematis that is in a lot of shade (until 4 pm) that is doing really well. Is it too steep to mulch?

I have 1 large Silver maple, 1 large Sugar maple, and used to have 5 large Norway maples in this yard. In my experience, there is a significant difference amongst the 3. The Silver maple is very greedy about water and has large gnarly surface roots that grow aggressively into the gardens that are irrigated. These trees have a high anaerobic tolerance, can tolerate seasonal flooding, and I wouldn't worry in the slightest about piling mulch or soil in the root zone (1 foot of soil is a bit much - on the other hand, the roots might be gleeful to have more soil to grow into). I also regularly hack away at large roots to cut them back from the perennials and septic system, with little apparent effect. It's not easy to grow under these trees, but drought tolerant plants do okay. The Sugar maple has much more well-behaved roots. Only, these trees don't tolerate root disturbance, salt, suffocation, or compaction. I dug out 2 large Burning bush from one side of this tree and within months it suffered die back on the trunk on that side and a strip of bark peeled off. So I only dig gently around this tree or not at all. Norways are near impossible. They have dense shade, allelopathic roots, and they suck the soil dry. Not to mention they are extremely invasive. I had 4 of them cut down. The only thing growing happily in the root zone of the remaining tree is Vinca minor. I love the native maples, but they aren't easy to garden under, and I'm not interested in pampering plants to be able to do so. But I have other places to garden.

I hope no one minds my making a push for native plants, especially under a native tree like Silver Maple. Very happy under our Silver Maple: Golden Groundsel, False Solomon's Seal, American Spikenard, Oakleaf Hydrangea, Pagoda Dogwood, Spicebush, Bluestem Goldenrod, White Snakeroot, Wood Aster, Sweet Joe Pye Weed, Native Columbine, Royal Ferns, Cardinal Flower, Dwarf Crested Iris. Birds love this area with all the underplantings, and plants that supply lots of caterpillars for their young, and berries later. Also great for bees and butterflies. One trick is putting a bird bath under the tree, and putting some of the plants needing extra moisture, like the Cardinal Flower, near that so they get watered when you hose the bird bath. I am actually trying to get rid of the lily of the valley that is also there, that was there when we moved in. It is super-poisonous to pets, and looks just awful after it's done blooming. I wish we could totally eradicate it.

Big maples are atrocious root zone "hogs". If it's anything like the ones I have (had, got rid of several) you will need an axe to get even the smallest planting hole dug. For ones I needed to retain for shade, I ran a Cat 1 middleplow about 20' out from the trunk and severed the roots. Probably not applicable to your situation - although you could do the same thing with a rented ditch witch - but it does stop the roots from robbing water and nutrients beyond the line. Easy to see in summer where the side near the tree has brown grass and the side past the cut has green grass. Of course you only want to do this to 50% or less of the tree's root zone. Alternately you can just do what you've done, which is to water whatever you plant under them scrupulously. For me that wasn't really an option because that area of my garden is over 200' away from any hose taps.