If you are referring to the shade of deciduous trees, it is not a problem. They don't produce as many flowers in the shade, but they will grow up to 15ft. or more in height.
To compensate for the reduced chlorophyll production in the shade, they would probably benefit from 2 or 3 applications of a balanced fertilizer each year.
The species and it's tall cultivars have a rather open branch structure. Annual pruning or "topping" of the plants can increase their fullness and width, but if fast growth is desired, you might suggest two rows of plants, 3 or 4ft. apart, with one row offset to cover the center of the other row.
Rb

Hemlocks make for a nice screen although, they may be a bit expensive. I have used Loropetalum chinense in Buckhead with partial sun and had similar growth to full sun.

Cherry laurel is a nice evergreen plant that tolerates shade. The cultivar Prunus caroliniana 'Compacta' is more dense.

Thank you all so much! We'll look at all of these - though I am very fond of loropetalum.