Perennial Fall Chores

Carol O'Meara, Colorado State University Extension

Carol O’Meara, Colorado State University Extension

BOULDER COUNTY – Perfect gardeners are those that work with the rhythm of the seasons, rolling with the vagaries of the weather. Rain or sun doesn’t ruffle their feathers; they simply are one with the earth and its little mood swings.

I am not a perfect gardener. If I were, the lingering heat wave wouldn’t bother me. But I’m shocked at the temperatures whenever I step outside, my mind insisting that Mother Nature is going to have to use the same calendar as the rest of us, darn it, and start cooling off. This deep into September, it’s time to start planning for fall, not hosting a pool party.

Each season brings with it a list of chores that promote good plant health, and in fall, perennial beds and borders should be rejuvenated with a little late season planting and cleanup. Local garden centers offer an excellent assortment of these long-lived plants, bringing in fresh material for shoppers’ delight.

Cleaning up after plants stop growing for the season removes insects, their eggs, and any diseases that over-winter on fallen leaves. But in good gardener fashion, there are several schools of thought on how to care for perennial beds in fall. For those who like their beds tidy, cutting back the foliage once it is dead gives it a neat appearance over the winter.

Others subscribe to the “do-it-later” tack of leaving all the plants in place, frozen into a winter tableau of browned leaves, spent seed heads, and dried flowers. Both techniques have pros and cons; cutting some perennials back will open up stems to drying winds of winter and accelerate winter-kill, while leaving dead, decomposing plants in the garden increases risk of spreading disease.

But the biggest advantage for leaving plants standing into winter is the nesting sites they provide for overwintering pollinators. Many solitary bees use hollow stems to lay eggs, and leaving stems standing is a good way to help pollinators throughout the winter. Clean up other garden debris, such as fallen leaves, to remove the risk of plant diseases.

Hedge your bets by cutting some perennials back after it dies to the ground but leave ornamental grasses, seed heads of Rudbeckia, Echinacea, or poppies until late winter for texture and food for birds. If you do this, leave only healthy plants standing; if they’re diseased, remove them and throw them out.

Leaving your plant clean up until spring 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.

Dig and store tender summer flowering bulbs and corms after frost has nipped the foliage and leaves are blackened. Gladiolas, cannas, and caladiums need to be lifted and kept in a cool location over winter. Dig carefully to avoid injuring corms since wounds are often entry points for disease organisms. Clip off and destroy plant tops immediately, then let the bulbs dry for a few days before storing them in a cool, dry area.

Our Colorado Master Gardener program in Boulder County is currently taking applications for the spring class. If you are interested in helping others garden, the Colorado Master Gardener program is for you! Classes run January through March and will be held every Friday, 8:30 a.m. to 4 p.m. Please contact the Colorado State University Extension Office in Boulder County at 303-678-6238 to receive an application.

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, e-mail [email protected] or visit