“Dabney! No! Wait!” Just kidding. Dabney Blanton, our lovely and talented horticulturist, knows not to prune the Artemisia in the autumn.
I imagine most gardeners have experienced a frost or freeze by now [exceptions: our Southern Hemisphere readers (howdy to Jimbo)…or anyone in the deeeeep south].
The perennials here in Blacksburg have taken a couple of hits; time to start trimming things back. In the Hahn Horticulture Garden and in my own personal garden, we like to leave perennials and ornamental grasses up as long as possible – gives us something to look at besides mulch, plus the wee birdies enjoy it.
But some perennials just look yucky after a freeze.
Case in point: foliage of the popular perennial Artemisia ‘Powis Castle’ resembles graying Kleenexes, hanging on the tips of the branches. HOWEVER, do not cut this back in the fall. It, like many other shrubby perennials, is sensitive to early winter whacking, in my experience, Buddleia and Caryopteris also fall into this category. Apparently the severe pruning sends a message to the plant to break bud – new shoots can appear and then “zap!” Wait until new buds appear in the spring, and be careful not to cut back too hard. I’ve killed a few that way, thinking I was doing them a favor.
“Cut ‘em back, cut ‘em back, waaaaay back!”
The best resource ever on maintaining perennials is Tracy DiSabato-Aust’s The Well-tended Perennial Garden. I should get kickbacks, as much as I’ve promoted this book! Truly a wealth of info – when should you cut it back, will it rebloom if deadheaded, don’t do [whatever] or you’ll kill it – all broken out by genus. Outstanding!
The Well-Tended Perennial Garden is completely great! For subshrubs like artemisia, caryopteris, perovskia, lavender, etc., I also look to the April 2005 issue of Fine Gardening, in which Debra Knapke had a great article called Pruning Subshrubs, that outlines just when, why, how, etc. to deal with these plants.
I was going to make a point about pruning subshrubs, but it seems Deb beat me to it! And I love leaving ornamental grasses in over winter down here too – I think they add great form to a garden in an otherwise drab time of year. We had a pretty mild winter this year. We also had above average winter rainfall – something that hasn't happened down here for almost 10 years. The difference in spring gardens this year as opposed to the previous ten has been absolutely amazing. So much thriving plant life this year, it's wonderful.
Some other common plants best left up: Heucheras, Hardy Chrysanthemums & Hibiscus, Roses (except deadwood) in zone 5 or colder.
This is where zone differences start showing up. It's perfectly fine to prune back our native (or Pacific NW native-similar) species, because they've gone dormant. They won't break bud until they've received their cold requirement. But marginally-hardy non-natives can indeed get the wrong message, since they don't have a winter hardiness mechanism to keep them from regrowing.
Great comments, all!
It's usually February around here before the grasses and "structural" perennials (Sedum 'Autumn Joy', Echinacea, Solidago 'Fireworks' etc.) get cut back. When the first daffs bloom ('Feb. Gold'), we commence chopping!