Invasive plants are a state of mind because everyone sees life from a different perspective and plants only become invasive because people don't pay attention. Woody plants may not bloom except in sunny areas which I presume you have if the soil is cracked and one that I beleive would do well in a sunny location would be potentilla fruticosa varieties, 4 diffenet colors. Vinca would be ideal if you learn how to control it, because it will double in two years under optimum conditions. I have included a website that might give you some ideas of additional perennials.

Here is a link that might be useful: Propagating Perennials

Vinca will escape very happily into your woods.

Steep slope, shade, dry, and competing with maples - yikes! Can't imagine much tougher conditions to grow anything, but I agree that Vinca minor and Bishop's weed would probably grow there. However, they are both invasive and I wouldn't recommend planting them. If you saw how much Vinca I am pulling out/smothering/mowing down in my yard. Decades of benign neglect on the part of the previous owner and I have thousands of square feet of it.

A couple native perennials that might grow there are Blue Wood Aster (Aster cordifolius) and White snakeroot (Eupatorium rugosum). Both reseed prolifically and will tolerate dry shade. Not sure about shrubs.

If it is not dense shade, you might consider the native shrub Symphoricarpos albus (Snowberry). It is tolerant of difficult conditions and hardy to zone 3. I find the blue-green color of the leaves a nice complement to the brighter greens of ferns, etc. The white berries are nice, too. It will spread by suckering, but probably not too much with a lot of competition from maples, etc.

-Caroline

Here is a link that might be useful: snowberry

I'm in your zone (4), have clay soil, and dry shade populated with mature maples -- so I thought I'd share what is surviving under mine.

1. Hostas (and the large blue species ones reseed prolifically!)
2. Ostrich fern (I would not have expected a fern to tolerate dry shade, but they have been colonizing nicely!)
3. Thalictrum aquilegiafolium
4. Lily of the Valley (careful, here - they are invasive, but can handle this tough environment!)
5. Lamium maculatum is doing well, but prefers the brighter parts of the shaded area. It is a true ground cover (spreader), unlike plants 1-3 I mentioned.

Hope this helps! I've had this area planted for many years now, and these are what have survived/thrived under these conditions.

Regards,
- Becky

I also have zone 4 mn, clay, dry shade and can second Becky's suggestions for Hosta (if deer are not an issue), Ostrich fern, Lamium (weeds still grow through this).

I'd also recommend you look at Pulmonaria, and epimidium, which grow quickly and can be split to fill an area. Also macrorrhizum geranium which spreads on it's own very nicely on my dry slope.

Another one I've considered but do not have yet and sounds like it can get away from you is Sorbaria sorbifolia--Ural False Spirea.

Good luck and remember that for at least the first season you'll need to water to get it established.

Thanks so much, everyone! I think I will probably not really get going on planting this slope until next year - right now it's the only way to reach my backyard area with heavy equipment, and I have a retaining wall that needs replacing...and it's not in the budget this year, what with Phase I of the landscaping, etc., going on. But I love the suggestions and will take a look for the ones with which I'm not yet familiar. I am having the front and other (north) side of my house landscaped professionally this year, and some of the plants you've mentioned will be used there, so they are good thoughts for bringing some unity. The front of the house has a short, semi-shaded lawn that runs pretty quickly into a deep slope to shaded, leaf-covered woods - we're putting ostrich ferns as a sort of soft divider between the lawn and the leaves. On the north side of the house, there's a very long bed that will have, among other things, epimedium x rubrum, as well as some snowberry shrubs. I do also have lilies of the valley at the base of my (u-shaped) driveway that I'm encouraging to grow more. And finally, I (I am a beginner here!) actually bought and planted some hostas for another area in the front. I am getting way ahead of myself looking at this section of the property, but after walking around the whole area and accessing parts I don't usually see (while pulling bags and bags worth of garlic mustard), I was pretty appalled at the state of that hill.

those of you with this somewhat dry, clay soil - how did you prep the soil before planting? Is this something I should start on this year, for planting next year? Should I weed and dig down and mulch, etc.?

For areas like that, I would cover with newspapers topped off with mulch. The newspapers will kill the weeds and with the mulch will get the soil in better condition for planting next year.
Ferns are an excellent idea for such a bank - I dug some up along the highway (NY ferns?) that are very decorative and spread. Also, deer don't eat them. I also like sweet woodruff - a pretty little plant which spreads but is easy to pull up if you don't want it to go further. And you can make May wine with the flowers.

can you provide a picture? I'm curious whether your situation is like mine. If it approximates it, I've had a success I'll be glad to tell you more about. But start with oldroser's recommendation. Get tons of newspapers, open each section in half, so what you lay down is about 4-5 pages thick. Overlap and cover with at least 2 inches of mulch. By next spring, you'll have a couple of inches of decent material to plant in and no weeds. So start gathering every neighbor's papers each week, or go to the grocery and get cardboard boxes and break them down. Hire a couple of strong, responsible teenagers. With help you can prepare the hillside in a few days, for a lot less money than any landscaper can. It works! If money is an issue, call a tree removal company and see if they'll dump a load of wood chips. These are coarse, but free, and in a year they;ll be dark. You could spend a fortune on good quality mulch, and it really is not necessary. Put it towards some beautiful viburnums next year.

My prep of areas depends on a number of factors - how steep that section is, how easy it is to access either from top or bottom, how picky is the plant I'm planning to put there and how quickly I want it to fill in.

In the steepest sections or parts that are hard to access there has been no prep, just perch myself carefully with two feet and one hand then dig a small depression and plug in plant. Not easy work.

In other sections I've used cardboard with leaf mulch on top - that works really well. In yet another area that was somewhat flat I built a big compost pile, then the next year I spread it out right there and planted the area.

By the time you are ready to do the back section, the Ostrich fern out front will have multiplied enough to move some.

If it's your only access to the back, you may not want to put expensive or hard to replace plants in case you do have to run machines over the area again.