Putting your Colorado garden to bed for the winter

Autumn weather so far is resembling summer, other than the brief cold snap last month.

Along with recent 80-degree days, there are dangerous fires still burning in parts of the state. The city of Fort Collins is on water restrictions because of drought, the Cameron Peak fire and the maintenance project on the Horsetooth Reservoir.

Next week, temperatures should cool to the 60s with little to no moisture relief in sight.

Will sweater and parka weather arrive soon? Your guess is as good as mine. It is Colorado, after all, and winter can arrive any minute, impolitely skipping a gradual cool-wet fall season that gardeners and landscape plants prefer.

Let’s all make the best of it: Get some exercise outside on these beautiful October days and put the landscape to bed properly.


Our landscapes are dry. We’ve had only one moisture-producing storm of late along the Front Range. (You remember Sept. 8 and 9, when it snowed and gardeners quietly cursed.) For an already dry region that only receives roughly 15 inches of precipitation yearly, we are currently at 7½ inches. Nature has some catching up to do.

Landscape plant roots absolutely need to be moist going into cold weather prior to the ground freezing. Dry roots can spell disaster for perennial plants that went in the ground this past spring, summer or last week. Dry tree roots, coupled with lack of winter moisture, can lead to root and branch death, less foliage, scorched foliage, no foliage or no tree next year.

If you are unsure if your landscape is dry, the simplest way to assess is to poke a screwdriver straight down in landscaped areas, like mulched beds, lawns and around trees. If it goes down easily, you’re probably not too dry. Conversely, if you’re using a bit of effort, there’s your answer.

Water all plants weekly until temperatures remain below 40 degrees and decent rain and snow arrive. Water deeply so all landscapes plants enter winter with adequate soil moisture. Trees need to be watered to a depth of 12 inches. For all other landscape plants, apply water so that the plant itself, and close-by surrounding soil, is moist to a depth of a couple of inches (not wet, but moist). A 2- to 4-inch layer of organic mulch like shredded bark or chopped leaves mixed with chemical-free lawn clippings are readily becoming available as trees shed leaves and you’re still mowing.

If you are new to Colorado, winters can be bone dry for long stretches. That means you need to drag out the hoses and give every plant another deep drink or two between snow events.

Garden cleanup

It is a gardener’s choice whether to cut back ornamental perennials with dead foliage in the fall or spring. Plants receive additional insulation and protection from our frequent freeze/thaw winter cycles when foliage is left in place. Snow-covered foliage can also add interest during the winter months. Birds appreciate seed heads and using the foliage for screening.

Any recent spring- or fall-planted perennials and shrubs should not be cut back in the fall.

Do not cut back woody plants, including butterfly bush, culinary sage, lavender and other late-summer or fall-blooming plants. Established perennials that may have had a disease like powdery mildew or harbored pest insects can be cut back in the fall, including plants like bee balm, phlox, salvia and Japanese anemone.

Remove spent vegetables, all the foliage (even dropped leaves) and roots from the vegetable garden. Toss in the garbage if diseased; if not, add to the compost pile. Root vegetables that are up and growing (beets, carrots and parsnips) and hardy spinach can be thickly mulched with good-draining organic materials (6-8 inches) and harvested through the cold months or until the ground freezes. There might be time to seed very quick-maturing leafy greens and radishes before that next snow arrives.

Continue enjoying summer- and fall-planted lettuce, mesclun mixes and mustard, then let them go to seed; next spring, dropped seeds may germinate and reward you with an early crop.

The days are about numbered for any remaining tomatoes, peppers, eggplant and other warm-season edible vegetables and herbs. If you are still covering at night and they are ripening, keep harvesting but preserve the extras. Preserve Smart is a helpful, local website to guide you through all types of preserving how-tos for fruit, vegetables and herbs.

Clean off vegetable cages, posts, stakes, trellises and garden tools, then disinfect before putting away for the season. Plant diseases can winter over. Mix a gallon of water with a half cup of bleach in a sprayer or wipe all supports and tools. Rinse with water, dry in the sun and store.

Planting and plant care

The rock star of many cuisines is garlic, and it’s one of the easiest herbs to plant for all levels of gardeners. Fall is also the best time to plant garlic to give it nine to 10 months to grow into large, healthy bulbs. There are several garlic varieties to grow at home that fall under the category of being either hard-neck or soft-neck. Their tastes vary (they’re all good) and once you try home-grown garlic, you’ll never be satisfied with what’s sold in grocery stores. Start with healthy garlic planting stock, sold only at reputable garden centers and online. Avoid planting garlic from grocery stores; many are sprayed or treated to prolonged storage. Next spring when you harvest, save some of the healthiest bulbs to replant in the fall again; garlic is truly a self-sustaining crop for gardeners.

Plant the leftover, smaller garlic cloves indoors in a container and grow indoors as quick-maturing garlic chives. Plant several cloves in one container. Just poke cloves down in the soil (pointy side up) a half-inch or so and water. Place under grow lights or near a sunny window.

Shallots have a mild onion flavor and are easily grown at home like garlic. Purchase shallot planting stock, just like garlic. Fall plant in Zone 5 or warmer an inch or 2 deep, 6 to 8 inches apart in a sunny location. Mulch with a 3-inch layer of shredded leaves (renew through the winter) and water if moisture is scarce.

Continue planting spring-blooming bulbs until the ground freezes solid, which can be anytime through November or possibly December. Your planting efforts now will be well rewarded next spring. Label the plantings so you know where they are located. To deter critters like squirrels, voles and mice from bothering newly planted flowering bulbs, place chicken wire over the planting hole, or sprinkle or roll each bulb in an animal-repellant powder during planting. Sprinkle more repellant or hot pepper flakes on top of the soil and grab any tunics from bulbs that fell off near the planting site, since even the smell from the tunics can attract them.

Use your own plants as a seed source. Many annual, perennial and herb flower seeds grown over the summer are easy to collect, store and use next spring. Cut off mature, dried seed heads from milkweed seed pods, moonflowers, cosmos, zinnias, dill and garlic chives. Break open and shake seeds into a paper bag and transfer to jars or envelopes. Label, then store in a cool, dry place.

Mid- to late fall is a great time to directly seed outdoors native wildflowers, grasses and perennials. Carefully read seed packages and avoid seeds of plants that become invasive.

Winterize hardy water lilies so the rhizomes don’t freeze or dry out by lowering them to the deepest part of the pond (at least a foot or more) or move them into a garage or cellar where temperatures remain around forty degrees.

After a few freezing nights, dig up non-winter-hardy summer bulbs, including gladiola, cannas, tuberous begonias and dahlia. Dry for a few days and place in boxes or crates filled with sawdust, vermiculite or perlite in a cool, dry place where they will not freeze over the winter.

General landscape

Get in your sprinkler company’s queue if you’re not a DIY and schedule draining and winterizing water features and automatic sprinkler systems.

Many homeowners choose to drain their pipes or use an air compressor to prepare automatic sprinkler systems for winter protection. Be aware that some compressors may not have the appropriate pressure and air volume needed to completely blow out all the water. If not blown out completely, costly damage can cause pipes, fittings or pumps to crack or burst. Too much air pressure may cause the nozzles to blow off.

Air compressor pounds per square inch should range from 40 to 80 pounds, depending on the type of pipes (rigid PVC or flexible black pipe) and nozzles installed on the system. Check the manufacturer’s home page for the ratings. Also, if just relying on draining the system, know that over time sprinkler lines may settle, creating low spots and possible areas for water to remain in the pipes.

Fall lawn aeration followed by fertilization is very beneficial before winter. The fertilizer moves into the holes left from the plugs and gets right to the root system. Be sure the lawn is moist to pull deeper plugs. Water the lawn a day or two prior to aeration.

Rake leaves from the lawn often or as soon as the trees are bare. A mass of heavy leaves that remain during the winter can smother and damage the lawn.

In my book, fallen leaves rank high on my “never throw away” list. Rake them into paper bags and take to a leaf drop, where they are used for low-cost compost for others in the community. Or rake and toss them into a pile or hole and start your own compost pile to use in next spring’s garden. Don’t like to rake and bag? Dry leaves can be mowed into the lawn, adding back valuable organic matter to the soil. Set the mower height high and make several passes over the leaves.

This is truly tucking in the garden in fall: Run over dry leaves with the bag attachment which picks up lawn clippings, too. Place chicken wire around newly planted perennials and shrubs and place the mulched leaves inside the cage for extra plant insulation through the winter. And my favorite tip: Layer the leaf mixture over open soil in the vegetable area or other open areas to protect soil from blowing away. Water it after placing so it can freeze in place over time.

Avoid blowing leaves into the street or tossing them in the garbage; many municipalities have collection or drop off sites through early December. Denver leaf drop information is at 311 or denvergov.org.


October is a good month to prompt Christmas cactus to bloom anywhere from Thanksgiving to Christmas. They need cooler temperatures (68-degree nights) and nine hours of sunlight daily for approximately six weeks. Reduce watering when the flower buds form, then weekly as the buds swell. Flower color deepens when the plant can dry out between watering (too dry and the flowers will drop).

Take stem cuttings from outdoor annual geraniums for new plants next year. Root 4- to 6-inch cuttings in fresh potting soil and keep in bright light. Also take cuttings from coleus, fibrous begonias, sweet potato vine and place in water until rooted, then pot up and grow as houseplants near a sunny window.

Plant amaryllis bulbs indoors in October for December bloom. Shop now for the best selection.

Additional resources

  • The case for not cutting back perennials in the fall
  • Fall & winter watering
  • Planting garlic
  • Preserve smart
  • Re-blooming Christmas cactus

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