As aspen leaves turn gold and the first frosts sweep down from the Rockies, Colorado gardeners face one of the most rewarding seasons in the yard. Fall is the time to work with your landscape rather than against it by protecting plants, replenishing soil and setting the stage for a vibrant spring. But the old instinct to strip beds bare and haul every leaf to the curb is giving way to a more ecologically informed approach.
Researchers, horticulturists and conservationists increasingly encourage gardeners to balance tidiness with ecological benefit. In Colorado, where temperature swings are dramatic and native pollinators depend on winter habitat, thoughtful fall yard work pays dividends far beyond curb appeal.
Rethink the fall clean-up
Traditionally, fall clean-up meant cutting every perennial to the ground, bagging leaves and clearing debris to the curb. While that delivers a tidy appearance, it strips away valuable organic matter and destroys critical winter habitat. Many experts now recommend leaving some plant material standing until late winter or early spring.
Seed heads left on purple coneflower, blanket flower, black-eyed Susans and other seed-bearing perennials and grasses become a critical food source for finches, chickadees, sparrows, and other seed-eating birds through the leanest months of the year. Hollow or pithy stems found in many perennials can serve as winter shelter for native bees and other beneficial insects, many of which overwinter as larvae tucked inside old plant stalks. Even fallen leaves insulate plant roots while decomposing into rich humus. The challenge for Colorado gardeners is finding the right balance between aesthetics, pest prevention and ecosystem health.
Do cut back plants with diseased foliage (peonies with powdery mildew, for example) to prevent reinfection next year. Dispose of diseased material in the trash rather than compost it. Also remove dead, invasive or aggressively self-seeding plants before they drop seed. For everything else, consider leaving it standing through the season.
Make the most of fallen leaves
Few tasks define fall more than raking leaves. Across Colorado, aspen, cottonwood, maple, and ash trees can shed thousands of leaves in a single yard. On lawns, thick mats smother grass and can promote snow mold, especially through wet spells. Shred leaves with a mulching mower to feed your turf. Set the mower deck as high as possible and make multiple passes until green grass shows through the shredded layer.
In garden beds, a light layer of shredded leaves acts as natural mulch, insulating roots and conserving soil moisture while breaking down into humus over time. For wildlife, beneficial insects like butterfly caterpillars, moth pupae and beetles can overwinter in leaf litter. Piling leaves in corners or under shrubs creates refuges for these species.
If you have more leaves than your garden can handle, compost rather than send them to a landfill. Many municipalities offer seasonal leaf recycling programs. Check with your local municipality if you’re unsure whether your community participates.
Bulbs, tender plants and smart planting
Fall is prime planting time for spring-blooming bulbs. Tulips, daffodils, crocuses and hyacinths should be planted by mid-October along the Front Range and earlier at higher elevations. Plant them at a depth of two to three times the bulb’s diameter, and choose a spot with good drainage. Colorado’s clay soils can rot bulbs left in standing water. A light application of bone meal or a low-nitrogen, high-phosphorus fertilizer at planting gives roots a strong start. Don’t forget to water your new bulbs and perennials once or twice a month during extended winter dry spells.
Tender bulbs and tubers like dahlias, gladiolus, tuberous begonias, and cannas cannot survive Colorado winters in the ground. After the first killing frost blackens their foliage, wait for a dry day and gently lift them with a garden fork. Allow them to cure in a cool, dry spot for one to two weeks, then store in cardboard boxes with newspaper, vermiculite, or sawdust in a location that stays above freezing. A basement corner that stays around 45 to 50 degrees Fahrenheit is ideal. Check stored bulbs monthly and discard any showing signs of rot.
Fall lawn care
Cool-season grasses – like Kentucky bluegrass and tall fescue – enter their most active root growth period in fall, making September and October the best window for overseeding thin areas and aerating compacted soil. Aeration allows water, air and nutrients to penetrate more deeply, reducing runoff on Colorado’s often dry, hard soils. Because grass roots take up nutrients more efficiently during this active growth window, fertilization of Kentucky bluegrass and other cool-season grass lawns is ordinarily recommended in fall.
For those facing water restrictions, fertilizing and aerating aren’t strictly necessary, though it can still be worthwhile if you missed doing it in spring. The key is to consider the condition of your lawn: for mostly green or patchy lawns, apply fertilizer as recommended and water it in with a minimum of half an inch of water before any water cutoff takes effect. A lawn that is dormant or fully brown for a month or more won’t benefit from fertilizing since roots won’t take it up.
Continue mowing until growth stops, keeping turf at its recommended height. Cutting too short before winter stresses the grass and exposes its roots to temperature extremes. Stop irrigating warm-season grasses once they go dormant but continue deep, infrequent watering for cool-season lawns through October as water restrictions allow.
Protect trees and shrubs
Save major pruning of trees and shrubs for late winter when plants are fully dormant. Fall pruning can stimulate tender new growth that is easily killed by cold. However, it is wise to remove dead, damaged, or crossed branches now before heavy snow loads add weight. Pay special attention to limbs over structures, fences and walkways.
To prevent sunscald and frost cracks, wrap trunks of thin-barked and new trees with brown crepe paper wrap, available at garden centers. If vole damage is a problem, a cylinder of hardware cloth around the trunk will protect it.
Broadleaf evergreens like pine, spruce and junipers can suffer desiccation during Colorado’s windy, sunny winter days. An anti-desiccant spray applied in late October or November helps retain moisture in the foliage.
Water all trees and shrubs deeply before the ground freezes, and throughout the winter on days when the temperature exceeds 40 degrees and there has been no snow cover for four weeks. This single step significantly improves winter survival. An added benefit to winter watering your trees and shrubs is the water your lawn will receive because all those turf and woody roots are growing together.
Work with the season
Fall gardening is less about finishing up and more about setting intentions. Every bulb planted, every cover crop sown, every leaf left for a solitary bee to shelter under, and every tree and shrub watered deeply is an investment in next year’s garden. The season rewards those who pay attention to it and who resist the urge to leave nothing standing but bare soil. Let the garden rest on its own terms and it will reward you all the more come spring.
Pam Rosendal is a Colorado Master Gardener.
