9 Reasons Fall Is the Best Time to Plant in Southwest Colorado

September through mid-October is the best planting window of the year in the Four Corners. Soil is still warm, air is cooling, and roots keep growing until the ground freezes, which at our elevation is usually well into November. Trees, shrubs, perennials, spring bulbs, garlic, and cool-season greens all do better planted now than in May.

If you have been waiting for spring to plant that shade tree, stop waiting. In Southwest Colorado, fall planting gives trees, shrubs, and perennials a six-to-eight-week head start on root growth that spring planting simply cannot match. The plant you put in this month will be established and ready to handle next June’s heat. The same plant set out in May will still be recovering from transplant when the hot, dry wind arrives.

Gardens around Cortez, Dolores, and Mancos sit between roughly 6,000 and 7,500 feet, with alkaline clay soil, strong UV, and a short frost-free season. Those conditions make timing matter more here than in most of the country. Below are nine reasons fall wins, followed by a planting timeline, watering guidance from Colorado State University Extension, and answers to the questions we hear most at the nursery.

1. Warm Soil and Cool Air Are Exactly What Roots Want

Soil holds summer heat long after the air cools off. In late September, afternoon air in Cortez may be in the 60s while soil a few inches down is still in the 60s or higher. That combination is the single best condition for root growth.

Roots keep growing as long as soil temperature stays above about 40°F. In the lower valleys of Montezuma and La Plata counties, soil usually stays above that mark into November. A tree planted September 15 gets roughly two months of underground growth before winter shuts things down.

2. The Plant Only Has One Job: Grow Roots

Trees and shrubs alternate between root growth and top growth, and the two run on opposite schedules. Roots put on a flush of growth in fall as soil cools and moisture moderates, then slow through midwinter, then peak again in early spring before leaves open.

A spring-planted tree has to grow roots, push leaves, and survive its first Colorado summer all at once. A fall-planted tree skips that juggling act. With no leaves to support, every bit of stored energy goes into anchoring the plant in your soil.

3. Fall-Planted Trees Enter Summer Already Established

This reason matters most at our elevation. Spring in the Four Corners is short and unpredictable. A tree planted in May can face a late frost, then 90°F afternoons, then weeks of dry wind, all within its first month in the ground and before it has grown a single new root into the surrounding soil.

A tree planted this fall meets next June with a root system that has been spreading since September, plus another growth spurt in March and April. Most fall-planted tree failures we see are not from cold. They come from people who stop watering in October. Keep watering until the ground freezes and the survival math is heavily in your favor.

4. You Will Water Less, and Less Often

Cooler air and shorter days mean far less water lost through leaves and from the soil surface. A new perennial planted in late August at this elevation may need water every day for the first week. The same plant set out in late September usually settles in on two or three deep waterings a week, and the monsoon leftovers help in years when the storms show up.

The tradeoff is that fall and winter in Colorado are dry. CSU Extension notes that many areas get little or no snow cover between October and March, and new transplants are the plants most at risk from winter drought. Water new plantings on warm winter days when air temperature is above 40°F, and the soil is not frozen, about once or twice a month during dry stretches. Water slowly so it soaks 12 inches deep.

5. Fall Is the Only Right Time for Spring Bulbs and Garlic

Tulips, daffodils, crocus, alliums, and hyacinths need a cold period to bloom, and they need roots in place before the ground freezes. CSU Extension says September and October are the best months to plant bulbs in Colorado, and bulbs planted after October may not root well enough to flower. Wait until soil temperatures drop below about 60°F, which in Cortez and Dolores usually means late September or early October.

Garlic follows the same clock. We recommend getting cloves in the ground before October 15 in most Colorado locations so they can root before freeze-up. Hardneck varieties handle our winters best and give you scapes in early summer. Plant cloves pointed end up, 2 inches deep, 6 inches apart, and mulch with 3 to 4 inches of straw.

Browse the seeds and bulbs we carry for this region. Bulbs and seed garlic sell through quickly, and the largest bulbs produce the largest flowers, so shop early for the best pick.

6. Perennials Come Back Stronger the Following Spring

Perennials planted in September spend the fall building roots and generally return next spring larger and better rooted than the same plant set out in May. Fall is also the right time to divide overgrown peonies, iris, and daylilies and replant the divisions, which gives you free plants and a better-looking bed. Our perennials are selected for high-elevation Four Corners yards.

Plant at least six weeks before the ground freezes, water consistently for the first six to eight weeks, and mulch after planting to hold moisture. The one thing to avoid is planting and then leaving town for two weeks with no irrigation.

7. Fewer Weeds, Fewer Pests, and Easier Digging

Bindweed, kochia, and cheatgrass are winding down in September, so a new planting bed faces far less competition than one dug in May. Aphids, grasshoppers, and most fungal problems taper off when the nights are cooler. And soil that has baked all summer is drier and easier to dig than the cold, wet clay you fight in April.

Fall also gives you more usable working days. Spring here swings from snow to mud to wind, often in the same week. September and early October are usually the most stable, pleasant stretch of the whole year for outdoor work.

8. September Is the Best Value of the Year at the Nursery

Nursery stock is at its most mature in September. Trees and shrubs that have been growing in their containers all season are bigger and better rooted than they were in May. This is when we run Fall Gold, our loyalty rewards that are redeemable between September 15 and 30. It is the last promotion of the year, and it lands squarely in the best planting window we get.

Take a look at our trees and shrubs grown for this elevation, and read our drought-resistant tree planting tips before you dig.

9. Cool-Season Vegetables Taste Better After a Frost

Fall is a real growing season for food, not just for ornamentals. Spinach, kale, chard, arugula, lettuce, and radishes prefer temperatures between 55°F and 75°F and lose quality in summer heat, according to the CSU Extension Vegetable Planting Guide. Cold nights convert starches to sugars in kale, spinach, and carrots, which is why they taste sweeter after a light frost.

Radishes mature in 25 to 30 days, arugula in about 30, and leaf lettuce and spinach in 40 to 50. A row cover or low tunnel buys another three to four weeks and carries hardy greens well into October. Our own greenhouses produce greens through the winter for the Winter Market for the same reason.

How Do You Water Fall Plantings Through a Colorado Winter?

Winter dehydration, not cold, is the number one killer of fall-planted trees and shrubs in Southwest Colorado. The fix is simple but easy to forget once the leaves are down.

• Water deeply every 7 to 10 days from planting until the ground freezes, usually mid to late November at lower elevations.
• Water once or twice a month from December through March during dry spells, on days above 40°F, at midday so it soaks in before nightfall.
• Apply water slowly so it reaches 12 inches deep. A soaker hose or a bucket with a small hole works well.
• Mulch 3 to 4 inches deep over the root zone and keep it 3 to 6 inches away from trunks and stems.
• Evergreens, new transplants, and shallow-rooted trees like maples and birch need this the most.

The Short Version

Fall is the strongest planting window we get in Southwest Colorado. Warm soil and cool air let roots grow without competing with leaves, and a plant established in September is far better equipped for next June than one planted in May. Bulbs and garlic have no other option. The only rule not to skip is water: keep it up until the ground freezes, then check monthly through winter.

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. Bring a photo of the spot you want to plant, and we will help you match the tree or perennial to your soil, sun, and water. For more regional guidance, see our high-altitude growing tips and 10 soil secrets every gardener should know.

Frequently Asked Questions About Fall Planting in Southwest Colorado

When is the best time to plant trees in Southwest Colorado?

September 1 through mid-October is the best time to plant trees in the Cortez, Dolores, and Mancos area. Soil is still warm from summer, air temperatures are dropping, and roots have six to eight weeks to grow before the ground freezes in November. That head start is the main advantage over spring planting.

The rule is to plant at least six weeks before the ground freezes. At lower elevations in Montezuma County, that usually means getting trees in by October 15. Above 7,000 feet, aim for October 1. Container-grown trees are the best choice for fall; bare-root stock should wait for late winter. Dig the hole two to three times the width of the root ball but no deeper; set the root flare at or slightly above grade, backfill with native soil, and water deeply. Then keep watering every week or so until freeze-up, and once or twice a month on warm winter days.

Is it too late to plant perennials in September in Colorado?

No. September is one of the best months to plant perennials in Colorado as long as you can water regularly for the following six to eight weeks. Perennials planted now build roots through fall and generally come back larger next spring than plants set out in May.

Try to finish perennial planting by early October at Four Corners elevations, so plants have several weeks of root growth before the soil chills. Choose plants already showing good root development in the pot rather than fresh transplants. Water two to three times a week for the first month, then weekly until the ground freezes. Mulch 2 to 3 inches deep after planting. Skip high-nitrogen fertilizer, which pushes tender top growth that will not harden off before frost. Compost worked into the planting hole is the safer choice. Late-blooming perennials like sedum, agastache, Russian sage, and rudbeckia also feed pollinators during the September nectar gap.

When should I plant spring bulbs in Colorado?

Plant tulips, daffodils, crocus, and other spring bulbs from late September through late October in Colorado. Once soil temperatures drop below about 60°F. CSU Extension names September and October as the best months and warns that bulbs planted after October may not root well enough to bloom.

In the Four Corners, that usually means the first two or three weeks of October. Plant bulbs two to three times as deep as the bulb is tall, pointed end up, in a spot with good drainage and at least six hours of sun. Amend heavy clay with compost, using up to one-third compost by volume. CSU research shows bone meal is not effective in our alkaline soils, so use a phosphorus fertilizer at planting instead. Buy early for the best selection and choose the largest bulbs you can find, since bulb size predicts flower size. Water once after planting and again during dry stretches until the ground freezes.

When do you plant garlic in Southwest Colorado?

Plant garlic in Southwest Colorado between late September and October 15. CSU Extension recommends planting  cloves in the ground before mid-October so they can develop roots before the ground freezes. Too early and cloves may sprout before cold sets in; too late and they will not root enough to survive winter.

Hardneck varieties such as Music, German Extra Hardy, and Chesnok Red handle Four Corners winters best and produce edible scapes in early summer. Break bulbs into cloves the day you plant, keeping the papery skin on. Plant pointed end up, 2 inches deep and 6 inches apart, in loose soil with compost worked in. After the first hard frost, cover the bed with 3 to 4 inches of straw mulch. Water in at planting, then leave the bed mostly alone until spring. Harvest in July when the lower leaves brown, and cure bulbs for two to three weeks in a shaded, airy spot before storing.

Do fall-planted trees need water in winter in Colorado?

Yes. Fall-planted trees and shrubs need supplemental water through winter in Colorado. CSU Extension notes that most of the state gets little snow cover from October through March, and recent transplants are the plants most at risk from winter drought. Water once or twice a month during dry spells.

Water only when the air is above 40°F and the soil is not frozen, and do it around midday so moisture soaks in before nightfall. Apply water slowly over the root ball and a few feet beyond it until it has reached about 12 inches deep. A five-gallon bucket with a small hole in the bottom, set next to the trunk, is an easy way to deliver a slow soak. Evergreens lose water through their needles all winter and need this most. Plants that dry out over winter often look normal in April, then decline in June when heat arrives, so the damage is easy to misdiagnose.

What vegetables can I still plant in the fall in the Four Corners?

Fast-maturing, frost-tolerant crops are the best fall vegetables in the Four Corners: radishes, arugula, spinach, leaf lettuce, kale, and chard. Sow them from early August through mid-September and use row cover to extend harvest into October. Garlic is the other fall crop, planted in October for a July harvest.

Count backward from the first frost, which arrives in early October around Cortez and earlier at higher elevations. Add a week for germination and another 10 days for slower growth as days shorten. Radishes take 25 to 30 days, arugula about 30, and lettuce and spinach 40 to 50. Anything over 60 days to harvest needs a cold frame or hoop house. Cool nights improve flavor in these crops, and kale and spinach often taste better after a light frost. Keep seedbeds moist during the warm days of early September, since soil dries fast at this elevation.

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