Carol O'Meara - Colorado State University Extension

Carol O’Meara – Colorado State University Extension

BOULDER –  Stepping from my house I was stopped by the sight of a single, perfect flower on the lavender shrub next to the door.  The stem extended horizontally so the blossom would gently caress the leg of a passerby, a ghost reminding me of summer glory long past. “That’s odd,” I mused, “you’re supposed to be asleep in the ground.” It is, after all, time for Halloween.

Lifting my eyes, a niggling worry began to take shape: the roses are still in bloom. Like anyone in a horror movie, I didn’t take the hint, climbing into my car to go to work.  There, the penstemon was in full bloom, along with the chocolate flower (Berlandiera lyrata).  Reports of hyssop and pincushion flower blooming still, and iris flowering again came in to the Help Desk, setting off the theme from the Exorcist in my head.

As October closes and November dawns, it’s worse than putting a toddler to bed in the garden; the plants are refusing to lie down and go to sleep.  And if they don’t before deep cold hits, we’ll have a perennial version of the Walking Dead.

To help our plants, make sure they get water.  We’re still in a moderate drought and the days are warm enough to keep the plants growing.  But whatever you do, don’t deadhead them.  Yes, those late roses are tempting and would make a lovely centerpiece.  Deadheading and pruning encourage new growth, which won’t be hardened off for the winter.  Put down the pruners and back away.

There are several schools of thought on how to care for perennials once they’ve gone dormant for the winter.  For those who like their beds well-made, cutting back the foliage once it’s dead gives it a neat, tidy appearance.  Others subscribe to the “heck-with-it” philosophy of leaving all the plants in place, frozen into a winter tableau of browned leaves, spent seed heads, and crisp flowers.

Both have their strengths and drawbacks – cutting some perennials back will open up stems to drying winds of our winters and accelerate winter-kill.  However, leaving dead, decomposing plants in the garden may increase risk of splashing/blowing fungal spores and other diseases.

How to achieve balance?  After perennial foliage dies off, you can remove it, though you might want to leave ornamental grasses, seed heads of Rudbeckia, Echinacea, or poppies until late winter for the texture and food for birds they provide.  One note of caution – leave only the healthy ones to stand.  If they are diseased, remove them and throw them out.  Birds may appreciate a nice seed snack, but nobody, bird or human alike, appreciates a disease filled meal.

Leaving your plant clean up until spring also allows the plant to capture more snow, funneling moisture to the soil. Snow, along with mulch, gathered at the base of plants sitting close to each other in a winter garden also gives them some added protection from wind.  After the ground freezes, apply mulch to stabilize soil temperature and prevent alternate freezing and thawing of soil, which can lift crowns above soil levels.

In Colorado, roses do not have to be capped for winter protection, and, due to our intense, sunny days, capping is discouraged.  The best protection for roses against winter kill, particularly for the hybrid teas and grandifloras, is to mulch over the bud union and lower portion of the canes to a height of six to eight inches with loose soil, leaves, or similar material. This protection is particularly important in late winter and early spring to protect the vital parts of the plants from extreme changes in temperatures.

Colorado State University Extension, together with Boulder County Parks and Open Space, provides unbiased, research-based information about consumer and family issues, horticulture, natural resources, agriculture and
4-H youth development. For more information contact Extension at the Boulder County Fairgrounds, 9595 Nelson Rd., Box B, Longmont, 303.678.6238, or visit