Clumping bamboo might work for your shady area if they can be grown in your area. They won't take over your yard like runners can.

Is your south slope compacted badly? Is it clay soil or something else?

I forgot I was still on the NW forum, so bamboo should grow just fine for you.

Japanese Holly, Ilex crenata, 'Convexa' keeps fairly dense in shade and responds well to shearing.
Formal Gardening under a large Acer macrophylla is going to be difficult. Besides the heavy shade, you're going to have to deal with roots and big leaves and winged seeds on the ground in the fall. You may want to rethink it.

Adding gravel to muddy ground won't make it drain better. Increase the slope and contour it as much as possible to direct the moisture away and down the slope. Where is the water coming from?
My neighbor put gravel in a puddle expecting it to drain away because of the rocks. He ended up with a puddle full of rocks.

I'm not sure what you mean by a gravel bed? I've heard terms like rain or bog garden as well as swell for drainage problems. I've read suggestions to dig down, make a pebble pool or line with a pond liner & add soil back for moisture loving plants. I just didn't have the heart to collect more water there, so did something different for our a similar drainage problem where grass would just rot in winter & die off despite additions of compost, aeration, etc.

Did you plant moisture loving or bog plants in the poor drainage area? Hosta and astilbe can take full sun if moist here in the NW. Many plants we consider shade plants are shade tolerant and would do fine in sun if moist. Dogwood might also help. Might also need to add more compost and organic matter so you have loam instead with sand added as well to give space in those soil particles.

I just picked up 28 bags of sand from Craigslist for amending my lasagna soil for a new herb bed. I am tired already & haven't unloaded the Suburban. I've posted a want herbs -trade garden supplies on the PNW Plant Exchange site if you have herbs & want some of what I have to offer.

Back to what we did for the beds in the low area...We've created a gravel path & mounded up lasagna style soil on both sides of it. In two spots we dug dry wells, so that the rain would fill them instead our driveway & lawn. We think we need to dig some in the gravel driveway as well to contain the flow from the top of the road as our place is low & the rest is higher.

Problem of water only during rain storms now, so we've made progress. The water has to go somewhere and surface of gravel is hard pan, not loose gravel anymore. Plantings are doing just fine and don't appear to be rotting in wet soil, though the combination of our clay + amendments is keeping the soil moist when I dig down to make a planting hole.

One other thing we've not done is divert the downspout flow to the dry well or to another area of that garden.

Let me know if you need pics. I've not yet taken any.

Does that help?
Corrine

The master gardener's site has some shrubs that do well in poor drainage. They also have another list for typical wet in winter, dry in summer, soils. I really like Aronia Viking for fruit, mine is in a very dry area in summer and gets little supplemental water. It is deciduous. I am considering getting a native barberry, Berberis fendleri, for fruit and hedge, it is also deciduous and gets large. The barberries are thorny so that makes them a good deer hedge. Some of the Asian ones are evergreen. Most probably need good drainage, perhaps if you correct the drainage they would work. The Ninebark or Red Osier dogwood on the list below sound good.
----------------From link-
Moisture-Loving Shrubs. Here are a variety of shrubs that can thrive with moist or wet conditions throughout the year, including poor drainage.
Aronia arbutifolia (red chokeberry)
Aronia melanocarpa (black chokeberry)
Aronia x prunifolia (purple chokeberry)
Calycanthus floridus (carolina allspice)
Clethra alnifolia (sweet pepperbush)
Cornus alba and cultivars (redtwig dogwood)
Cornus stolonifera and cultivars (red osier dogwood)
Lonicera involucrata (black twinberry)
Myrica californica (california wax myrtle)
Physocarpus opulifolius and cultivars (ninebark)
Salix discolor (pussy willow)
Salix purpurea (arctic willow)
Sambucus nigra (black elderberry)
Sambucus racemosa (red elderberry)
Sorbaria sorbifolia (false spirea)
Vaccinium corymbosum (high bush blueberry)

Here is a link that might be useful: shrubs for tough conditions

Planting larger plants that like wet soil can help suck the water out so it's not so mucky. Willows in particular, but they aren't using water in winter. They'd dry it out in spring once they leaf out. Red cedars and sitka spruce like damp soils and are active in winter. These get to be very very big trees though.

Dry wells to give the water a place to go as mentioned above. Just adding gravel to the soil won't do anything except give you wet muddy gravel. Perlite and compost both hold water, so would only improve drainage if the drainage is bad because the soil is a compacted clay. If the drainage is bad because there's a hardpan underneath, then adding perlite or ocmpost just makes the soil even muckier.

Our drainage problem was so bad that we were getting water under the house. The previous owners had piled up dirt and planted plants. Our contractor dug out all the soil on that side, like 5 or 6 feet down and 3 feet wide, then put in drain pipes with holes to take the water down to a lower level. He then had pipes in the lower system coming off the upper system to disburse the water. He then filled the upper side with rock, with treated lumber beside it. That solved all of our problems. I have now come out 3 more feet from the drain field and put a row of sasanqua camellias so that I do not have to look at the drain field. I would not try to plant over a drainage problem if it is near the house!