7 Things Every Southwest Colorado Gardener Should Do Before Winter

Most winter plant loss in the Four Corners comes from drought and sun, not cold. Between October and March, Cortez, Dolores, and Mancos often go weeks without snow cover while the sun stays strong and the wind keeps blowing. Skipping fall watering, mulching, or wrapping often means your plants won’t leaf out in the spring.

The good news is that winter prep at our elevation is mostly about seven tasks, and most of them take an afternoon. Get them done between now and the ground freezing, usually mid to late November at lower elevations in Montezuma and La Plata counties, and your trees, perennials, and vegetable beds will come through in far better shape.

Below is the list in the order we recommend tackling it, with timing for gardens between 6,000 and 7,500 feet, watering numbers from Colorado State University Extension, and answers to the questions we hear most at the nursery this time of year. If you still have planting to do, read our post on why fall is the best time to plant in Southwest Colorado first, then come back here.

1. Keep Watering Until the Ground Freezes

The single most important thing you can do before winter is to keep watering or continue to water watering in October. Irrigation systems get shut down, leaves drop, and it is easy to assume plants are done for the year. Roots are not. They keep growing until soil temperature falls below about 40°F, and they need moisture to do it.

Water trees, shrubs, and perennials deeply every 7 to 10 days from now until the ground freezes. For trees, CSU Extension recommends about 10 gallons of water per inch of trunk diameter at each watering. A 2-inch caliper tree gets 20 gallons. Apply it slowly over the root zone so it soaks 12 inches deep rather than running off our clay.

Anything planted this year, all evergreens, and shallow-rooted trees like maple, birch, and aspen are the highest priority. These plants are most likely to show winter drought damage next June, when it is too late to fix.

2. Set Up a Winter Watering Routine Now

Fall watering is only half the job. CSU Extension notes that many Colorado locations get little or no snow cover between October and March, and dry soil during that stretch is what kills new transplants and stresses evergreens. Decide now how you will water starting in December, before the hoses are packed away and the routine is forgotten.

The rules are simple:

• Water once or twice a month from December through March during dry spells.
• Only water when the temperature is above 40°F, and the soil is not frozen.
• Water at midday so moisture soaks in before nighttime freezing.
• Use a five-gallon bucket with a small hole, a soaker hose, or a slow trickle from a hose you reconnect for the afternoon.

Plants that dry out over winter often look fine in April and then decline in June, so the damage is easy to blame on something else.

3. Mulch Beds and Root Zones After the First Hard Frost

Mulch is the cheapest winter insurance you can buy, but timing matters. Applied too early, it keeps soil warm and delays dormancy. Applied after the ground has cooled and the first few hard frosts have hit, usually late October to mid-November here, it holds soil temperature steady, slows moisture loss, and prevents the freeze-thaw heaving that pushes shallow-rooted perennials out of the ground.

Spread 3 to 4 inches of shredded bark, wood chips, or straw over the root zones of trees and shrubs and across perennial beds. Keep mulch 3 to 6 inches away from trunks and crowns so it does not trap moisture against bark and stems. Newly planted perennials, strawberries, garlic beds, and marginally hardy plants like lavender and some salvias benefit the most.

If you have leaves, shred them with the mower and use those. They are free, and they improve the soil as they break down.

4. Wrap Young and Thin-Barked Trees Against Sunscald

Sunscald is one of the most common tree injuries we see in the Four Corners, and it is entirely preventable. On a clear January afternoon, our strong high-elevation sun warms the south and southwest side of a trunk enough to wake up the cells beneath the bark. When the sun drops and temperatures crash, those cells freeze and die. The result is a long, sunken, cracked strip of dead bark that shows up in spring and invites borers and disease.

Young trees and thin-barked species are the most vulnerable: maples, honeylocust, ash, linden, crabapples, and all fruit trees. CSU Extension recommends wrapping the trunk from the ground to the first branches with commercial tree wrap in late October or November and removing it in April. Start at the base and overlap upward like shingles so water sheds off. Do not leave wrap on through summer, where it holds moisture and hides insect damage.

Plan to wrap any tree you have planted in the last three or four years.

5. Drain Irrigation, Store Hoses, and Protect Spigots

Spending an hour winterizing your irrigation system in the fall saves you the spring headache of frozen drip lines and split sprinkler heads. 

Work through this checklist before the first hard freeze:

• Shut off the water supply to your irrigation system and open the drain valves.
• Blow out sprinkler lines with compressed air or have a professional do it. Drip systems can often be drained by opening end caps and letting gravity work.
• Disconnect all garden hoses from spigots, drain them, and store them out of the sun.
• Cover outdoor spigots with foam faucet covers or an old towel and a bag.
• Empty and store rain barrels so ice does not crack them.

Keep one hose accessible and drained for winter watering days. A hose that lives in the garage and gets hooked up for an afternoon during colder months is all you need.

6. Clean Up the Vegetable Garden and Feed the Soil

The vegetable garden is where fall cleanup pays off most. Diseased tomato vines, squash foliage with powdery mildew, and spent plants left standing over winter give pests and pathogens a place to overwinter. Pull them, and put anything diseased in the trash rather than the compost pile.

The best time of year to buy soil is when beds are clear. Spread 2 to 3 inches of compost over each bed and either work it in lightly or leave it on the surface for worms and freeze-thaw cycles to incorporate. Our alkaline clay improves a little every year you do this. Fall is also a good time for a soil test, since results come back faster than in spring and you can amend before planting. Our post on 10 soil secrets every gardener should know covers what to add and what to skip.

If you can get it done by early October, sow a cover crop of winter rye or a rye and hairy vetch mix. It holds soil through the windy season, adds organic matter, and gets turned under in April. Spread straw or shredded leaves over unplanted beds to protect topsoil from winter wind erosion.

7. Move Tender Plants and Containers Before the First Frost

The first frost in the Cortez and Dolores area typically arrives in early October, and earlier above 7,000 feet. Protect or bring inside all cold-sensitive plants before temperatures plunge, not the morning after.

Bring porch-dwelling houseplants and tropicals indoors while nighttime lows remain in the 40s. Check them for aphids, spider mites, and whiteflies first, rinse the foliage, and give them a week in a garage or covered area to adjust before moving them to a sunny window. Bring in geraniums and other annuals you want to overwinter the same way.

Empty ceramic and terracotta pots, or move them somewhere dry. Wet soil expands when it freezes and cracks pottery. Perennials in containers are far less winter-hardy than the same plant in the ground, so sink the pot into a garden bed, move it against a north wall, or cluster pots together and mulch over them. Hybrid tea roses need a 10-to-12-inch mound of soil or compost over the crown after the first hard frost; shrub roses and most natives can be left alone.

The Short Version

Winter in Southwest Colorado is dry, sunny, and windy more than it is bitterly cold, so protect your garden for those conditions. Keep watering until the ground freezes and once or twice a month after that. Mulch after the first hard frosts. Wrap young tree trunks. Drain the irrigation, clean up the vegetable beds, and get tender plants indoors before the first frost in early October. Seven tasks, one or two weekends, and a much better spring.

Stop by Four Seasons Greenhouse & Nursery at 26650 Road P between Cortez and Dolores, open 9 a.m. to 5 p.m. seven days a week, or call (970) 565-8274. Fresh greenhouse produce continues through winter, and the Winter Market opens November 1.

Frequently Asked Questions About Preparing a Garden for Winter in Southwest Colorado

When does the ground freeze in Southwest Colorado?

In the lower valleys around Cortez, Dolores, and Mancos, the ground usually freezes solid in mid to late November. Soil above 7,000 feet can freeze in early November. The first killing frost arrives earlier, typically the first week of October, but soil holds heat much longer than air does.

That gap between first frost and ground freeze is your winter prep window. Roots continue growing as long as soil temperature stays above about 40°F, so trees and perennials are still actively using water through most of November even though the tops look dormant. Plan to finish deep watering, mulching, and tree wrapping by Thanksgiving in most years. Ground freeze also varies a lot from year to year and from one side of a property to another. A south-facing bed against a wall may stay workable weeks longer than a shaded north slope. If you can push a trowel in, roots are still active, and the plant can still take up water.

How often should I water trees in winter in Colorado?

Water trees once or twice a month from December through March in Colorado, during dry stretches with no snow cover. CSU Extension recommends about 10 gallons per inch of trunk diameter at each watering, applied only when air temperature is above 40°F, and the soil is not frozen.

Water at midday so it soaks in before evening temperatures drop. Apply it slowly over the entire root zone, which extends well past the drip line on established trees, rather than dumping it at the base of the trunk. A five-gallon bucket with a small hole drilled in the bottom delivers a slow soak with no attention. Newly planted trees, evergreens, and shallow-rooted species like maple, birch, aspen, and spruce need this most. Established native trees like piñon and juniper generally do fine without it. If a month goes by with a good snowfall that melts into the soil, you can skip that watering. The goal is to keep the root zone from drying out completely, not to keep it saturated.

Should I cut back perennials in the fall or leave them?

Leave most perennials standing until spring. The stems and seed heads protect the crown from cold and wind, trap snow for insulation, feed birds, and shelter overwintering native bees and beneficial insects. Cut them back in March or April once new growth appears at the base.

There are exceptions. Cut back anything that had foliar disease this year, such as peonies with botrytis or bee balm with powdery mildew, and dispose of the debris in the trash. Cut your iris leaves back to about 6 inches to remove overwintering iris borer eggs. Hostas and daylilies collapse into mush after frost and are easier to clean up in fall than in spring. Ornamental grasses, coneflower, black-eyed Susan, sedum, Russian sage, agastache, and yarrow all look good through winter and should stay. If you prefer a tidier look, compromise by cutting back the front of the bed and leaving the back. Leave leaf litter under shrubs where you can, since many pollinators overwinter in it.

How do I protect roses for winter in Colorado?

Mound 10 to 12 inches of soil, compost, or shredded bark over the base of hybrid tea, floribunda, and grandiflora roses after the first hard frost, usually late October to early November in the Cortez area. Water deeply first. Remove the mound gradually in April as growth begins.

Do not prune roses hard in fall. Trim only canes long enough to whip around in the wind, cutting them to about 24 to 30 inches, and save real pruning for spring after you can see what survived. Stop fertilizing by mid-August so the plant hardens off. Rose collars filled with mulch work well in exposed sites, and an extra layer of straw or evergreen boughs over the mound helps above 7,000 feet. Shrub roses, rugosas, and most own-root landscape roses are hardy in the Four Corners without mounding, though a layer of mulch over the root zone and a monthly winter watering still help. Freezing temperatures threaten grafted roses because winter cold easily destroys the tender bud union. Set the union 2 inches below grade at planting and the whole job gets easier.

Can I still plant garlic and bulbs in October in Southwest Colorado?

Yes, October is the right month. Plant garlic and spring bulbs by October 15 in the Cortez, Dolores, and Mancos area. 

Wait for soil temperatures to drop below about 60°F, which usually happens by early October at our elevation. Plant garlic cloves pointed end up, 2 inches deep and 6 inches apart, and cover the bed with 3 to 4 inches of straw after the first hard frost. Hardneck varieties handle our winters best. Plant tulips, daffodils, crocus, and alliums two to three times as deep as the bulb is tall in a spot with good drainage. Skip bone meal in our alkaline soil and use a phosphorus fertilizer at planting instead. Water once after planting and again during dry stretches until the ground freezes. Choose the largest bulbs you can find, since bulb size predicts flower size.

What should I do with my vegetable garden at the end of the season?

Pull spent and diseased plants, add 2 to 3 inches of compost, and cover bare soil with a cover crop, straw, or shredded leaves. Fall soil building does more for next year’s harvest than anything you can do in spring, and it protects beds from wind erosion all winter.

Dispose of tomato, squash, and cucumber plants with disease in the trash rather than the compost pile, since blight and powdery mildew overwinter on debris. Compost healthy plant debris, or chop it up and leave it as protective mulch. Pull weeds before they set seed. If you have hardy greens like kale, spinach, or chard still producing, leave them and cover with row cover or a low tunnel; they will keep going into November and often taste sweeter after frost. Our guide to extending your growing season has more on that. Fall is also a good time to send off a soil test, note what grew well and where, and sketch next year’s rotation while it is fresh in your mind.

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