I started to reply to this a few days ago but am not sure I'm on the same page as the OP. I think of an understory planting as meant to set off the trunks of tall trees, not fill in all the space between them, effectively obscuring that nice, somewhat open, woodsy feeling. So, personally, I would not plant anything massive and lump-shaped like kerria or yew. I'd go for smaller, more open shapes, either low or with a few trunks, and ground-covers, like early spring bulbs, wild strawberry, or hellebores, around those. If your understory plants reach the height of your lower tree branches, and fill in that space, that's a totally different look, good for screening but not ... special. If that's what you want, then your plant list is fine, but if you want a real understory planting, that's something else completely. You might add ilex glabra to the list, it's a native, non-spiny evergreen that likes shade and always looks good. Black berries on females if males are also planted. I've got blueberries in light shade, and they do really well there, too, although the birds get most of the berries. Vaccinium is s a pretty shrub, with great fall color, and comes in many sizes.

American elm? Here is a picture that shows someone's hands so you can see if it matches the size of yours. Ulmus americana

Carolina buckthorn? Frangula caroliniana fka Rhamnus caroliniana Link This post was edited by marti8a on Sun, Oct 5, 14 at 22:01

I agree with the fellow. Here is why. The redbud, Forest Pansy will grow about 25ft wide. You can double check , by doing a google of the name. If you planted 3 ft from house the branches would have no where to grow. Start with of piece of graph paper and measure you house, lot, deck etc. and draw your back yard on the graph paper. Then make a list of the plants that you like, and find out their mature size and place the circle on your graph paper for each plant Use the mature size so that you have enough room for each shrub. Making a plan will allow you to select the right size plant for you beds. Work with the fellow at the local garden center. He propbably has expereience with which shrubs will do best in you conditions