What is behind the boxwood hedge? Is it a wall, fence, building? Japanese anemone 'Andrea Atkinson' is a tall single white one and will grow in part shade and not too dry soil. It will spread underground, however, which can be good or bad, depending on where it's planted. In my area it blooms in September. 'David' phlox might work as long as it got enough air circulation. It's a mid to late summer bloomer. White Regal lilies would be great for late spring. Those are a few suggestions, anyway.

Behind the hedge is my front porch. Just a short concrete step up (about 8-9 inches high off the ground.) Do anemones stay narrow, or do they get bushy like Phlox. It's hard to tell by googling pictures, because I always wonder how many plants are planted in the pic! Wondering if I could keep the plants narrow by limiting the amount I plant....

Other ideas I've come across (please advise) are allium and verbascum. Thank you for the lily idea---I can't believe I hadn't thought of them! That actually helps a lot!

Japanese anemones spread and spread from the root. They are not clumpers. One foot is an extremely narrow space. Hard to think of a perennial that will get tall enough to be seen but stay confined to a space that narrow except for lilies.

I agree that 1 foot is't enough room to grow much, besides you may have shrub roots in that space competing for nutrients and water

Yikes.... didn't realize it would be too small. :(
What about just lilies back there? If I plant 2 or 3 different varieties I could still have something blooming back there May-Sept. maybe?

It really sounds to me as though you only have room for the boxwood hedge, especially if you plan on continually grooming to keep it at a specific height... you'll need to walk behind the hedge to work on it, won't you? That'll be a lot easier if you can step into the 12" space without trying to dodge lilies.

Perhaps the way to go is to put something (perennial or annual) in pots behind the hedge. This way, you don't have to worry about root competition, the fact that the plant would be raised up a bit would take away some of the width lower down, you could move them for maintenance work on the hedge, and you could change it seasonally and always have something in bloom.

:)
Dee

Dee,
Brilliant suggestion.

What about obedient plant or cleome? They get tall, have nice white flowers and don't need to be staked.

The obedient plant spreads but pretty slowly if you have zone 5 clay soil. Cleome will reseed and not stay put, but you should be able to pull seedlings if you weed often enough.

Large white lilies may look nice. Orienpets are an oriental/trumpet lily hybrid that get tall without staking and don't spread wildly.

I might also consider white liatris for a spiky white bloom.

You've got tons of choices! And if they don't work for you, rip 'em out and try somethings else! That's part of the beauty of gardening, really.