I would say a combination of 'yellow archangel' (also called false lamium, and sometimes goutweed, though 'archangel' is what it's listed as in the hortiplex here) and crown vetch would be your best bet...liberally studded with yucca plants, if you can find a nice strong back to put them in place. they don't seem to mind clay soil as long as it's on a slope...

I'm a pennsy native, and the combination of slope and shale is daunting- my parents added the third S- shade. the archangel is the ONLY think that grows on their property besides mayapples...but I got my original plugs from a lady who had it in full sun as a groundcover for when the deer ate everything else.

groundcover roses, lavendar and artemesia also make good second-string choices, once the others have established themselves...

and I wouldn't worry about the weeds too much- my mom got over them when she retired, and just has me scythe things off at knee height round about july (going over there this weekend, the rain's been helping things along)

wish I were closer (I'm out on the delaware) I'd come give you a hand!

Cround Vetch is bad news and takes over ajoining open areas and refuses to be removed from where it is not wanted. I would not reccomend planting it, as it is very invasive and exludes everything else where it grows densely-including yucca, wich might be crowded out in a little as 3 years.

Table Mountain Pine Grows naturally that sort of ecotype (almost exlusivly actually) and has low sweeping limbs that prevent the rain from washing the soil away. its pretty and has great wildlife value, and would probably help stabilize the soil better than just low-growing weeds.

Other attractive shrubby plants that would go well with table mountain pine are: Bear oak (Quercus ilicifolia), mapleleaf viburnum (Viburnum acerifolium), and low sweet blueberry (Vaccinium angustifolium) are the most important stand components in the northern part of the range of Table Mountain pine and all are very attractive to humans and wldlife alike, unlike tha groutweed and crown vetch, wich would be reletevly unappealing to wildlife, and those plants invade and destroy existing wildlife habitat.
Yoy could try little bluestem as gass, tough it takes a few years before it really gets top growth going- it invests most of its early energy into root growth.

Here is a link that might be useful: IMPACTS AND THREATS POSED BY CORONILLA VARIA (Crown Vetch)

Heed the advice of LOL on Crown Vetch as it is almost evil in nature. (Sorry Chinagirl). Look into Gro-low sumac. It is extremely drought tolerant, spreads nearly 8' wide, and has a root system suited for slope retention. Excellent fall color is also a plus. Most weeds cannot compete with it, with the exception of crown vetch! It gets almost 3' high where I grow it. Early yellow flowers are ok but not worth writing home about. Good luck!

why is PA, the home of crown vetch (compliments of Penn State ag school, who were trying to develop a nitrogen-fixing, slope-holding ground cover)

the only place it doesn't seem to be a total pest?

low bush blueberry is a great idea, though- especially if there are younguns in the area who'd care to harvest them for a share of the spoils ;)

a low-growing sumac? ooh! yum! glorious ! MUCH prettier than crown vetch ;)!

Let's face it, neither low grow sumac or crown vetch is very pretty. I would not use the words yum and glorious to describe either. No disrespect intended lol.

Sometimes you have to pick from a short list of plant alternatives. Perhaps I am wrong about crown vetch, but I am seeing it advance at an alarming rate. Have seen it overtake groundcovers, invade grass, continue up a hill of shrubs. I am beginning to think it is the worst weed I have ever had to deal with. ooh! yummy!

I agree with sage lover about crown vetch. A nasty weed.

Has anyone suggested sedum? There are many varieties in various heights and would make a lovely pattern.

Check this site out- low prices on small groundcover plants.

They say they're well rated by GardenWatchdog-

Here is a link that might be useful: Classy Groundcovers

I'm also in zone 5 in NY and have a similar problem to you - steep slope along driveway, major soil erosion and grass won't grow but I also have a group of Norway maples that are nutrient hogs and provide heavy shade. Three years ago I planted a combination of pachyasandra, vinca and ajuga. The vinca has been winning the battle on being fruitful and multiplying without any terracing or special treatment. But it's been a slow process. One thing I am tempted to try this fall is to lay down landscape fabric over a part of my slope and then create holes in the fabric to plant additional vinca. The fabric prevents self-sowing so any vinca I plant will have to grow upwards and sideways, but I'm thinking the fabric may prevent the soil and nutrient run-off so I'm going to give it a try.

Hey I am apparantly from the same area as you---getting older too---steep roadside bank too---clay rocks and fullsun. I planted creeping phlox, daffodils, grape hyacinths, and daylillies. Purple coneflowers reseeded onto the bank and I have also started transplanting Iris. They all do great. What I did was spray a total vegetation killer in a blocked out area at a time (an area I knew I would be able to get planted that season) It has taken me 3 seasons, but I am on my last small area. The last 20 feet!!! I had a 220' stretch of bank to do. The plants all do well on their own, the creeping phlox keeps the weeds down, while allowing the iris, daylilies and coneflowers to come up through. Please don't put that awful crownvetch in---it is one of the worst things to kill off, as bad as creeping charlie. Ann

While it may be useful on highway cuts, it should be against the law to sell crown vetch to civilians! Terrible, invasive stuff.
Rhus aromatica 'Gro-lo' is attractive. And another shrubby spreader is Hypericum calycinum. Good for exactly the situation described.

Juniperus horizontalis 'Bar Harbor'

There are also other low spreading groundcover junipers that have yellow and blue foliage to give a tapastry effect. This is assuming you want to plant it and leave it and not be out tinkering in it as they are prickly.

You can also interplant with heathers, Calluna vulgaris.
They are evergreen, love good drainage and sun and bloom and are hardy to zone 4 mostly. Ericas aren't all hardy, you want Callunas.

Oops. 'Bar Harbor' is blue, contrast with bright green and yellow.