Ask Mr. Smarty Plants

You might want to just plant shrubs that will grow in your poor soil.  You can mulch them with your composted horse manure to give them a little boost.  They will survive with less care than if you put them in pots.  I think you will still have to protect them by putting three or four stakes and a six foot fence in a circle around each plant until it is big enough that a few horse nibbles doesn’t decimate the entire plant. The fence will have to be five or six feet tall and be large enough in diameter to prevent the horses from reaching the plant, even as it grows wider.  I can find what is not poisonous for your horses in Cornell’s list of toxic plants, but I don’t think there is a definitive list of what horses won’t eat.  I could find they eat everything from roses to palmettos.  You might want to join some forums for horse owners and ask them if the horses will eat these plants.  I suspect horses are like deer.  There are no plants that some deer,  somewhere, won't eat.

Here are a few shrubs that will grow in your soil and not be poisonous to your horses. They all are perennials. That’s one of the neatest things about natives.  There are always many that are adapted to your soil, no matter how problematic it is for gardening.

1)      Smooth Sumac, Rhus glabra.  This makes a large enough plant to look good against the front of your barn. It grows in waste soils but mulching it will make it grow even better.

2)      Atlantic ninebark Physocarpus opulifolius – this fast-growing plant will grow in dry clay soils and is insect and disease resistant.

3)      Leadplant amorpha, Amorpha canescens. This is another beautiful shrub.  It likes rocky, well-drained soils.  You might want to plant it in small mounds to make sure it has enough drainage.  I usually just dig a hole about half as deep as I need, then mound the soil to the top of the dirt around the plant.

If these plants don’t fit your landscaping scheme, you might want to look at the recommended plant list for Missouri which I already narrowed down to plants that are perennials, want full sun and dry soils. You could combine several of these.  But I suggest that you check to see if they will grow in rocky clay and go ahead and plant them in the ground.  The horses will probably eat the grasses, and some of the wildflowers.  But sideoats gamma is supposed to grow better when the land is overgrazed so may survive being eaten to regrow.  Just be sure to check each plant to see if it is poisonous to horses.

You might want to try these sources to find your plants:

Missouri Department of Conservation/ George O. White State Forest Nursery

Missouri Wildflower Nursery

Rhus glabra

Physocarpus opulifolius

Amorpha canescens