Ask Mr. Smarty Plants

First, read our How-To Article on Gardening with Native Plants. Next, since you specified high wildlife value, read our How-To Articles on Wildlife Gardening and Butterfly Gardening. We are not civil engineers so the slope values are a foreign language. You would have to make your own decisions on whether a tree would tolerate being planted on a sloped surface. Since we recommend only plants native not only to North America but to those areas where the plant grows naturally, we will go to our Native Plant Database and, using the parameters you have given us of sun (6 hours or more of sun a day) and part shade (2 to 6 hours), native to Maryland in the various habits (shrub, tree, herbaceous blooming perennials) and give you some examples for each. Once you have become acquainted with our Native Plant Database, you will be able to make your own selections. Follow each plant link on our list to determine the growing conditions for that plant, light, water needs, etc. before making a decision.

We would suggest that you first map out the sunny and/or part shade areas of your plot, watching it for a few days and noting the times on your map to make choices more relevant to the space. The clay soil is going to be a problem, and we recommend that you amend any area where you are planting with a good quality organic compost to assist in drainage and to allow the new young rootlets air space in the soil in which to extend. We regret that you have ruled out grasses, as they are the very best plants for controlling erosion, with their long fibrous roots. Just in case, we are going to recommend a couple of grasses that  would not be mowed  but are ornamental. We will also throw in a vine that might go at the top of the steeper slope and trail down and some low groundcovers.

So, we will begin with herbaceous blooming plant (herbs). First round, we will go to our Native Plant Database, select on Maryland, herbs for Habit, both sun and partial shade for Light Requirements. There are other specifications you can put in such as expected height, bloom color and time or soil moisture, but we can only use the conditions you listed. One last bit of advice, Summer is not a good time to be planting, especially the woody plants, trees and shrubs.

Herbaceous blooming plants - Asclepias tuberosa (Butterflyweed) and Capsicum annuum (Chile pequin)

Shrubs - Callicarpa americana (American beautyberry) and Comptonia peregrina (Sweet fern)

Trees - Amelanchier laevis (Allegheny service-berry) and Cercis canadensis (Eastern redbud)

Grasses - Chasmanthium latifolium (Inland sea oats) and Muhlenbergia capillaris (Gulf muhly)

Vines - Bignonia capreolata (Crossvine) and Passiflora incarnata (Purple passionflower)

Low groundcover - Antennaria plantaginifolia (Plantain-leaf pussytoes) and Cornus canadensis (Bunchberry dogwood)