Euphorbia, that is. Why do I keep seeing gorgeous, thick clumps of chartreuse-blooming spurge all over the place, while the clump in my garden is....well...gangly would be the kindest way to describe it.
I've never quite known how to prune these beauties, and each type has different requirements. Lower growing clumps can just be sheared down after blooming, or if they get mildewed. But how to deal with the willowy show-stopper Euphorbia characias ssp. wulfenii?
My favorite all-time pruning book, The American Horticultural Society Pruning and Training, by Christopher Brickell (DK Publishing) to the rescue...Turns out that wulfenii stems are biennial, meaning that they develop in one year and flower the next. Here's my mistake - the stems should never be shortened; in midsummer, after the chartreuse flower domes have finished blooming, simply cut down spent stems to speed up the plant's natural cycle of renewal. Each bloomed-out stem should be cut down to the base of the plant. This won't look as bad as it sounds, because you should leave in place all the stems that haven't yet bloomed. And don't worry, this is a vigorous plant that will regenerate quickly.
So as soon as the flowers on this lanky wulfenii in my Whidbey garden fade, I'll cut it back to the ground. Remember, ALWAYS wear gloves when pruning any euphorbia, because the stems bleed an irritating, milky substance that can cause a nasty rash.