not sure you do prune Wallflowers..I would think digging clumps out would be it..and now would be fine...I imagine you could prune them now to if you really wanted to...as well...for the most part just cut out the non producing parts..cutting the tops off will most likely cause them to flourish to the sides...etc.

I thought gardeners bought a fresh lot of wallflowers at this time of the year' for next year' and discarded this years wallflowers. There is a perennial form of wallflower, perhaps you mean that type?

If it's the perennial ones, they don't take kindly to pruning. They're short-lived plants anyway, so just keep dead-heading, take cuttings if possible, or else discard them when they get too woody.