The Colorado Winter Garden

winterpansiesN7285Winter allows Colorado gardeners to rest—much like their gardens. But our approaching winter, coming after a summer drought, has forced gardeners to reconsider time-honored approaches. Horticultural experts are suggesting that we leave perennial beds alone, allowing the top growth to bend over and protect roots throughout the dry months. Applying mulches, winter watering and establishing a compost bin all take on an urgency. This winter, more than ever, requires planning for spring.


Although some gardeners have cut back perennials and shrubs as a matter of fall cleanup, this may be the year to let your perennials shelter each other. Nature encourages grasses and shrubs to sweep over one another as a winter blanket. Precious moisture is conserved and dry winters lose their ferocity. The birds will thank you, too, since seed heads and rose hips provide winter food.

wintergrassesbending7289“Leave your perennials to catch more snow,” says Robert Cox, Colorado State University horticultural agent for Jefferson County. “Like snow fencing, you can do a bit of water harvesting. Another school of thought believes that all the snow that ends up on the foliage evaporates before it reaches the ground. So you can cut back halfway to the ground. Either idea is valid.”

Harriet MacMillan, horticulturist at Echter’s Greenhouse in Arvada, adds, “I only remove the tops of foliage if there is an excess of debris. Unless you can see that snow will not get down to the roots of the plants, you can leave the foliage.”

wintersage7286The plants best suited to survive a dry winter are drought-resistant. That includes Colorado native plants as well as the exotic ornamentals like Russian sage (Perovskia‘Blue Spire’). Many of the Mediterranean herbs are hardy, too. Culinary sage is still useable in the garden now—the perfect accompaniment to holiday feasts. Thyme, oregano and mint will persevere through dry spells and even parsley, which requires much more water, will stay green for harvesting long after other crops have died.

Marilyn Raff, author of “The Intuitive Gardener,” adds compost during the winter to her perennials. “I try to give up to six inches of compost around the roots of shrub roses. But the grasses I leave until March, then I cut them from six to 12 inches to rejuvenate them,” she says.


winterrosehips7282In contrast, a vegetable garden left unattended through winter provides a cover for pests and disease. It’s still recommended that kitchen gardeners dispose of tomato vines and other plant debris that may protect the egg sacs of insects. But stripping the soil of all covering without snow is a recipe for erosion, so try planting a cover crop of rye, vetch or clover. It’s not too late.

“They will green up and grow in the spring,” says Carol O’Meara, Colorado State Extension assistant horticultural agent for Boulder County, “and although rye usually is the quickest to germinate, they will have such a long period of striation through the winter that any of those would be okay.” Striation is a period of cold that is required for some seeds to germinate.


Most gardeners are bracing for another summer of drought. But we may also have a winter of drought. Dry winds and meager snowfall are sure to damage trees and shrubs. “We are still recommending hand watering for shrubs and trees,” Carol says. Some tips will help trees to survive a tough winter and prepare for a difficult spring and summer, too. The website, sponsored by the Denver Water Board and CSU Extension gives information on winter care for shrubs and trees.

wintertrees7273Robert also recommends tree wraps for non-native young deciduous trees along the Front Range. Sunscald will damage a young tree up to three years of age. Usually found on the south or southeast side of a tree, the exposed trunk will appear bleached in spots. “Sunscald is not a problem in other parts of the country, but a tree wrap is beneficial here. Our day temperatures can be in the 60s and the tree will try to come out of dormancy. Then at night when temperatures drop below freezing, the tree will try to go back into dormancy.” Wraps can be applied in late November and removed in March.

City trees like lindens have fared poorly, Robert says, while hawthorns, flowering pears and hackberry trees remain stalwart. His major concern is for the native ponderosa and piñon pines. Both pines are drought-tolerant but four years of accumulative drought have weakened these tough mountain trees. Winters may be no better than summers when it comes to ongoing dry spells.

“Winter can be even more harmful to trees than summer,” Robert says, “Cold, dry spells are terrible for trees and shrubs. Water during an extended dry spell, say, three or four weeks.” In the metro areas, you’ll have to use a water device that is designed strictly for tree watering. Any sprinkler system has been banned.


Consider mulch to be your garden’s best friend in both winter and summer. Robert prefers bark mulch of varied sizes—like the chipped bits that come from tree trimmers. Pebbles, he says look nice “but hold the heat and make the plants warmer than they would be otherwise. The stuff that you buy bagged called bark mulch is expensive and the wind blows them. You can put down the mulch of tree trimmers about two and a half inches thick and cover that by more expensive mulch if you like that look.”

wintercompostbins7274Harriet never covers her perennials with mulch but simply spreads the mulch around the plant. “Perennials have a basal foliage—don’t cover that. Check perennials every four to six weeks and water as needed. We are learning that we don’t have to water as much as we once did, but we must water thoroughly.”

If you plant spinach seeds for an early spring harvest, or bulbs such as tulips, they will require regular watering all winter. Try to water when the temperature reaches 40 degrees. Otherwise, water will not filter through the soil but lie in a frozen pool on top. This is true for trees and shrubs as well.

In spring, expect to hear about drip irrigation. Farmers on the Western Slope are using drip irrigation for their wine grapes. Melon farmers in Rocky Ford have turned to drip irrigation, too. They dropped their use of water by 30 percent and gained a bumper yield. Drip irrigation is perfect for vegetable gardens, perennials, trees and shrubs.

And Robert says it may even by used for lawns, but will first be adopted by vegetable gardeners. “Instead of the hose being flat like the old soaker hose, drip irrigation hoses are round and porous to water. It’s great for vegetables because you can configure the hose to any way it fits your garden. Drip hoses don’t last a long time in sunlight. That’s why it’s recommended that they be covered by wood chip mulch.”

And finally, set up that compost bin that you’ve been meaning to get to. This is the perfect winter chore that will yield wonderful results in the future. Despite all the complicated literature out there, it’s remarkably easy. A wire bin will do. Fill it will leaves from the yard and kitchen vegetable scraps. Lemon rinds and pineapple peelings will take longer to decompose than tealeaves and coffee grinds. But eventually they will break down and provide terrific compost.

You’ll soon discover that there’s never quite enough compost for your needs. Marilyn buys compost by the truckload and spreads it throughout her garden all winter long.

Winter gardening doesn’t demand as much from us as the vigorous growing season, but there’s work to be accomplished. Marilyn recommends checking on the garden periodically for water needs, or to cut back a shrub or ornamental grass as needed. Perennials like Joe Pye weed(Eupatorium purpureum) might be cut back half in winter, then cut more severely in the spring. “It can be a gradual process,” she says, about pruning, watering and mulching, “there’s plenty to do in the winter.”