It's the roots that hold the soil.

It may be too late to plant in your zone, and anything planted now will not have time to grow enough to hold the soil this winter. You could get some jute fabric and stake it down over the slope to help hold it for now.

Thanks so much - that's a big help!

Val

Val, I agree with Creatix, the jute will definitely slow down or stop erosion for now. When the time comes for planting you can leave it in place and cut a hole in it wherever you want to plant something. That way it will keep working for you until your plants have time to establish and spread. It will eventually just rot away naturally. If you use wooden stakes you would not have to remove them either.
Cheers.
Dee.

There is a large list of plants that would be suitable in your area for use as a permanent and evergreen groundcover. You will have the best luck at erosion control if you chose a sturdy broadleaf or needleleaf evergreen. Use a biodegradable erosion control netting over the winter and plant in the spring.

What's at the top of the slope? And what is the pitch of the slope?

If the batter is not too great you could lay bundles of brushy twigs across the slope pinned down by rocks or hoops of stiff wire. They will definitely slow the flow and catch any debris from further uphill.

If the top of the slope is on your property consider planting there as well - something with fibrous roots. It doesn't have to be long-lived, either. If the area gets good sun, grasses could be useful as a start. Lupins also, if they do well in your area and the soil is light enough. They're not strong on clay, however.

Another possible is to put small untreated poles across the slope and wedge them in place to break the flow, catch the soil, build a settling area which will be a bit more level for planting. Over time the logs rot away, adding to the soil fertility and stability.

Vines may be useful - even the traditionally 'weedy' sorts, if you can keep them checked. Parthenocissus, Hedera, Clematis, Vitis - and ones which root as they go are worth considering, too.

If you are going to plant into the slope, think about cutting an L-shape rather than a basin, with the long leg of the L against the slope. The short leg makes a flat surface for planting into. Works well in clay.

First up, though, see if you can reduce the water flow from upslope. It may be useful to form an ephemeral soak with associated bog-dwelling plants and trees to blot up most of it. Alders, small willows and similar sturdy damp lovers.

I am a bamboo lover... and if I were you, that's what I will do.

I will go look for some cold hardy running kind of bamboos and plant them all over the slope there are different type of bamboos, do some home works about bamboos and which kind you like and which will survive the winter in your zone... you don't have to plant a whole lot of them now, but when these bamboos shoot up their new canes comes next spring, you can transplant them and help them spread, running bamboos are known for their Erosion controls... also the benefit of it is when you have a lot of them, you can dig some of them up and sell them on Ebay :) in fact, that's how I got mine from!

This is my 2 cents and hope it helps

Roger from AR