Answer: There are any number of shrubs you could use, depending on the growing conditions where you are putting the arbor and the overall look you want to achieve. Often you will see roses or clematis or other vining plants trained on an arbor to grow up it and trail gracefully at the top. Then to each side you might see a fairly symmetrical planting of a pyramidal evergreen and several smaller deciduous shrubs, possibly some flowers at the base as well. In a shady location however your choices are limited to plants that will do well in the amount of shade you have -- how long it is shady and at what time of day.
Unfortunately, hollies and most dwarf evergreens need full sun all day long or at least a half a day of direct sun to grow well, as do nearly all flowering vines and roses. For a truly shady location with little direct sun, your choices will be quite limited. You might try a pyramidal yew along with a three to four foot boxwood and possibly Hydrangea arborescens and perhaps some larger hostas. If the shade is from deciduous trees you could also try some early spring flowering bulbs to the front of the planting such as daffodils and crocus. If the shade is dappled light or brighter you might try a sweet autumn clematis on the arbor itself.
Your professionally trained nurseryman might also have some suggestions if you can bring him a photo of the arbor and its setting (marked with the direction north), approximate size of the area to be planted, and an idea of what is casting the shade -- building shade and tree shade are not quite the same. In the meantime, I hope this gives you some ideas.
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