I completely agree that it is a lot easier to select plants that will tolerate the conditions than it is to change the conditions on the hillside. However, some cut banks have newly exposed clay that might not support much vegetation for a number of years while natural processes slowly change a clay subsoil into a clay soil that can support plants. If this is the case, then you might need to do something to the soil to make planting wildflowers - even wildflowers adapted to clay - feasible. I would consider planting a cover crop. This would be a fast growing ANNUAL crop that will create lots of organic matter, break up the soil with its roots, then die. Oats are popular for this. Annual rye grass is too, but make sure you plant only annual rye, not perennial rye. You might need to break up or at least scratch the surface of the soil before you sow the seeds. I would plant the oats really thickly. For color you could add a few sunflowers to the oats - just use sunflower seed sold for feeding wild birds. Don't plant any perennial plants. If you ask around, you'll get lots of recommendations for perennial plants to cover slopes, and some of these would probably grow, but they would keep growing ifor years and prevent you from eventually planting wildlfowers. If the oats grow well this summer, next spring you can plant wildflower seeds into the dead oats. I'd select species that are native, tolerate clay, and you like. I would not plant any "wildflower" seed mix. Most of the seeds in mixes are not native, and many won't be well adapted for your hill. I think picking out species is the best part of the process and will entertain you over the winter. There are lots of websites that describe wildflowers and how to grow them. I usually try to compare several websites or books decribing each plant to make sure I know a little about each plant before I try to grow it. You can expect despite careful planning that some of the plants you select will thrive, while others won't grow well, This can't be avoided. Eventually you'll know what grows well and looks good on your hillside, but it will take a few years. If there are similar slopes in the area, check out what grows on them this summer for ideas. Expect that most of the plants along a road or behind a building will be non-n ative weeds you wouldn't want to plant, but a few will be natives.

Wildflowers do best if selected specifically for your area or growing conditions. For example, prairie type wildflowers are not as suitable for woodland conditions and west coast wildflowers not appropriate for southern or east coast gardens. The attached link has some very good info on wildflower types and for various parts of the country and climates. Not all wildflowers are equally hardy or even desirable in all locales. And planting time is generally going to be early spring as self-seeding annuals are often included in these mixes in a good percentage and they are unlikely to germinate well enough this late in the season. Otherwise you may want to contact your local (state?) dept. of natural resources or other center for native plant info. Native plants usually include a variety of wildflowers but tend to be better adapted to locale and often less weedy. IME, tossing down some wildflower seeds and ignoring them is not highly successful.......they may look good for the first season but are typically overcome by weeds and/or native plants in subsequent years and then look a mess. Here is a link that might be useful: wildflower gardening

Erodium.

Thanks all! One might rather choose to grow its near-relative Cosmos caudatus instead though, because it apparently has healthy, edible leaves that taste like mangoes!!! Cosmos caudatus has pale pink flowers – but it is mostly grown for its leaves. The young shoots taste refreshing. A friend likened its taste to that of a mango, and he’s right. I’d gladly eat a whole bunch of cosmos caudatus – it is that tasty, and more so since it is said to improve blood circulation, lower uric acid, reduce body ‘heat’ and is a good source of fibre.