I looked into the wood chip idea I just got a fresh truckload of them for Spring. A few things you can expect: The chips are rougher and coarser than store bought. If this bothers you, you can throw down a thick layer of the cheap stuff and then a thin coat of expensive ones on top. they come in various colors. After a while if you dig around in it you may see white/ off white threads running around in it, or worms crawling around down there, or even mushrooms on top of it. These are decomposers. They are busy changing it from wood chips into plant food. They won't bother you or your plants, they only like dead things. The chips start off a brightish white and fade slowly through grey and get soft and blackish as they meld into the soil. The only concern I have with wood chips is the runoff where the next grand canyon is forming -- it is a veritable river when it gets flowing A valid concern. Can you run a heap of rocks down the canyon for the water to flow through without moving them? Maybe have a series of lashed stick dams to let water through but hold the chips? Lay branches across it? I read that with chips you normally put down 4-6 inches of it on bare dirt. Would that be enough to prevent rushing water from carrying it away? I'm not sure. Or would I be better off building a temporary drainage system to route the water under the tree bed until the plants can grow outward and hold the soil together? Maybe lay a perforated pipe on top of the ground, bury it in chips? I guess I wrongfully assumed that I would need to plant the pachysandra all over the area, but your suggestion about letting it grow outward over several years sounds much more logical. There are various ways to handle this. The rings were meant to give you something decorative, something orderly to look at while it's developing. You could plant them in a loose even scatter across the whole bed. This won't look like much at first but might be faster. You could buy and install more plants whenever it's convenient (you just move the chips out of the way and plant) You could subdivide and move the existing plants every few years. You could plant once and let them do their thing. They'll all work. Looking at the the second picture I see I misjudged something. I had thought the trees were centered in the bed. They're not, they're along one edge. This means a ring around each tree won't be starting them in the middle, it'll be starting along one side. This is not a deal breaker. You could do rings around the trees and start some sprinkled along the left side of that second picture so it keeps up with the tree side. Patience will be key. The rule of thump with Pachysandra is: The first year it sleeps. The second year it creeps. The third year it leaps. Thank you again for your reply. You've definitely given me a silver lining on what I thought would be a daunting and expensive project! I love it when this Internet stuff works. 8-)

If you live in the greater Seattle area or anywhere close to Puget Sound, you are zone 8. Zone 7 is not until you are up in the Cascade foothills. Woody groundcovers are the best for erosion control and these are never available by seed. A 75 degree slope is extremely steep and I would suggest using geotextiles to secure the slope before planting. Plants that could work for you are kinnikinnick (Arctostaphylos uva-ursi), bearberry (Cotoneaster dammeri), creeping raspberry (Rubus calycinoides), salal (Gaultheria shallon) and low Oregon grape (Mahonia repens). All will tolerate partial shade, all are evergreen and the kinnikinnick, salal and Oregon grape are native plants so minimal maintenance required once established. Another excellent plant for slope stabilization that is not a groundcover is our native western sword fern, Polystichum munitum.

Nature's answer is to cover it with any kind of plant material, but probably the most aggressive and invasive type, as that's what's trying to spread the most. To follow the same general principal in a more civilized kind of way, is to cover the area with some kind of groundcover. The difference is that you'll have to help the civilized plants along, watering them through the establishment period according to the weather patterns. What's coming to mind as a possibility, if it grows there, is ordinary fountain grass, Pennisetum setaceum. It gets about 3' tall with an equal spread, is easy to grow and reseeds itself, which helps it to fill in any bare spots that might appear. It's quite nice looking for a long period of time in a warm climate.

Susan - I don't think it's a settling issue. I'm at almost the bottom of a hill, and further down (and actually part of my yard) are some very large retention areas for water run-off. As far as I can tell, this is just water being water and finding the path of least resistance. There's actually a retaining wall between the backyard and the house... about 7 feet at the top where the deck is, down to around 2 feet at the corner of the house where there's a door to the basement. If I wanted to get professional advice... what sort of professional am I looking for? I do plan on eventually planting some bushes and other plants along the upslope part of the fence to provide a privacy screen between me an my neighbor, which may help some, but that is probably a few years away. Unless I decide that it becomes important as part of stabilizing the slope and shift my priorities around.