Colorado’s high altitude and cool nights make late May the best time to plant chrysanthemums, ensuring they survive the first frost. If you plant too early, a sudden spring snow can kill them. Too late, and the roots won’t establish before winter. This guide walks you through exactly when and how to plant mums in Colorado for vibrant fall blooms.
Chrysanthemums, or mums, are a fall favorite across the Front Range and mountain towns. But Colorado’s unique climate—with its intense sun, dry air, and unpredictable freezes—requires careful timing. The best time to plant chrysanthemum in Colorado is late May to early June, after the last frost date has passed in your area.
Best Time To Plant Chrysanthemum In Colorado
Let’s break down why late May works so well. Colorado’s last spring frost typically occurs between May 5 and May 20 in Denver and lower elevations. In higher mountain areas, it can be as late as June 10. Planting after this window gives mums time to root deeply before the heat of July and August.
Mums are photoperiodic—they bloom when nights get longer in late summer. If you plant them too late in June or July, they may not have enough time to grow strong roots and produce flowers before the first fall frost, which can hit as early as mid-September in some parts of Colorado.
Why Late May Is The Sweet Spot
Here are the key reasons late May planting works best:
- Soil temperatures are warm enough (above 50°F) for root growth
- Risk of a killing frost is low in most areas
- Mums have 12-14 weeks to establish before fall blooming
- They can handle the summer heat if watered consistently
- You avoid the stress of transplanting during peak summer heat
One common mistake is planting mums in early spring, like April. The soil is still cold, and a late snow can damage tender new growth. Another mistake is waiting until August, when you buy potted mums from garden centers. Those are already in bloom and won’t survive Colorado’s winter if planted that late.
Regional Variations Within Colorado
Colorado is not one climate. Your exact planting date depends on your elevation and location.
Denver Metro And Front Range (5,000-6,000 Feet)
Late May is ideal. The average last frost is around May 5-10. Plant after Mother’s Day for safety. You can push to early June if you’re in a colder pocket like Parker or Castle Rock.
Colorado Springs (6,000-7,000 Feet)
Plant in late May to early June. The last frost can be as late as May 15-20. Watch for cold snaps in early June.
Mountain Towns (8,000+ Feet)
Wait until mid-June. Places like Breckenridge, Leadville, and Estes Park can see frost into June. Plant after June 10 for best results.
Western Slope (Grand Junction, Montrose)
Late May works here too, but you may have warmer soil earlier. Still, stick to late May to avoid a surprise frost.
How To Plant Chrysanthemums In Colorado Soil
Once you’ve picked the right time, proper planting is crucial. Colorado soil is often clay-heavy or sandy, neither of which is ideal for mums. Here’s a step-by-step guide.
Step 1: Choose The Right Mum Variety
Not all mums are created equal for Colorado. Look for hardy garden mums, not florist mums. Hardy varieties like ‘Sheffield Pink’, ‘Ruby Mound’, and ‘Clara Curtis’ survive winter better. Florist mums are tender and usually die in Colorado’s cold.
Step 2: Prepare The Soil
Mums need well-draining soil. Colorado clay holds water and can rot roots. Mix in 2-3 inches of compost or aged manure. If your soil is sandy, add organic matter to retain moisture. Test the pH—mums prefer slightly acidic to neutral (6.5-7.0).
Step 3: Dig The Hole
Dig a hole twice as wide as the root ball but no deeper. Place the mum so the top of the root ball is level with the soil surface. Backfill with amended soil and press gently to remove air pockets.
Step 4: Water Thoroughly
After planting, water deeply. Mums need consistent moisture, especially in Colorado’s dry air. Water at the base, not on the leaves, to prevent fungal diseases. Use a soaker hose or drip irrigation for best results.
Step 5: Mulch To Protect Roots
Apply 2-3 inches of organic mulch like wood chips or straw. This keeps soil cool, retains moisture, and prevents weeds. In Colorado’s intense sun, mulch is a lifesaver for young mums.
Caring For Mums Through Colorado’s Summer
After planting in late May, your mums need regular care to thrive through the hot, dry summer.
Watering Schedule
Water mums deeply once or twice a week, depending on rainfall. Colorado gets little summer rain, so don’t rely on it. Check soil moisture 2 inches down—if dry, water. Avoid overhead watering to prevent powdery mildew.
Fertilizing
Feed mums with a balanced fertilizer (10-10-10) in early June and again in mid-July. Stop fertilizing after August 1 to encourage bud formation. Too much nitrogen late in the season produces leafy growth but few flowers.
Pinching For Bushy Growth
Pinch back the tips of stems when they reach 6 inches tall. This encourages branching and more blooms. Stop pinching by mid-July, or you’ll remove flower buds. In Colorado’s short growing season, timing matters.
Pest And Disease Management
Common issues in Colorado include aphids, spider mites, and powdery mildew. Spray aphids off with water or use insecticidal soap. For powdery mildew, ensure good air circulation and avoid wetting leaves. Colorado’s dry climate actually helps reduce fungal problems, but it’s still a risk.
Preparing Mums For Colorado’s Winter
Mums can survive Colorado’s cold winters if you prepare them correctly. The key is protecting the roots from freeze-thaw cycles.
Fall Care After Blooming
After the first hard frost, cut back the stems to 4-6 inches above the ground. Do not cut them to the ground—the stubs help catch snow and insulate the crown. Leave the foliage in place until spring.
Mulching For Winter
Apply a thick layer of mulch (4-6 inches) after the ground freezes. Use straw, leaves, or wood chips. This prevents heaving, where soil freezes and thaws, pushing roots out of the ground. In Colorado, heaving is a major cause of winter kill.
Container Mums
If you planted mums in pots, move them to a sheltered location like an unheated garage or against a south-facing wall. Wrap pots in burlap or bubble wrap to insulate roots. Water sparingly every few weeks if the soil is dry.
Common Mistakes When Planting Mums In Colorado
Avoid these pitfalls to ensure success.
- Planting too early in spring—wait until late May
- Using florist mums instead of hardy garden varieties
- Planting in heavy clay without amending soil
- Overwatering, which causes root rot in cool soil
- Not mulching for winter protection
- Fertilizing after August, which delays blooming
- Ignoring the first frost date in your specific area
One more thing: don’t buy mums in full bloom from garden centers in September and expect them to survive winter. Those are often forced blooms and won’t establish roots before the ground freezes. Plant in spring for perennial success.
Frequently Asked Questions
Can I Plant Chrysanthemums In Fall In Colorado?
It’s risky. Fall-planted mums often don’t have enough time to root before winter. If you must plant in fall, do it by early September and mulch heavily. But spring planting is far more reliable.
How Late Can I Plant Mums In Colorado?
The latest safe planting date is early June for most areas. If you plant after mid-June, the mums may not bloom before the first fall frost. For mountain areas, plant by early June.
Do Mums Come Back Every Year In Colorado?
Yes, if you choose hardy garden mums and protect them over winter. Many gardeners in Denver and Colorado Springs have success with perennial mums. Florist mums are annuals and won’t survive.
What Is The Best Mulch For Mums In Colorado?
Organic mulches like straw, shredded leaves, or wood chips work best. Avoid rock mulch, which heats up and dries out soil. Apply 4-6 inches after the ground freezes for winter protection.
Should I Water Mums In Winter In Colorado?
Only if there’s a prolonged dry spell. Colorado winters are dry, so a deep watering once a month on a warm day (above 40°F) can help roots. But don’t overwater—dormant mums need little moisture.
Final Thoughts On Planting Mums In Colorado
Timing is everything with mums in Colorado. Stick to late May for most areas, and you’ll give your plants the best chance to thrive. Prepare the soil, water consistently, and protect them over winter. With the right care, your mums will reward you with brilliant fall color year after year.
Remember, the best time to plant chrysanthemum in colorado is late May, but always check your local frost dates. A little planning now means a lot of blooms later. Happy gardening, and enjoy those autumn colors against Colorado’s blue skies.
If you have clay soil, don’t skip the compost. If you’re in the mountains, wait an extra week. And if you’re ever unsure, ask at your local nursery—they know your microclimate best. Mums are tough plants, but they need a good start in Colorado’s challenging conditions.
One last tip: plant mums in groups of three or more for a bold display. Space them 18-24 inches apart. They’ll fill in nicely by late summer. And don’t forget to deadhead spent blooms to encourage more flowers until the first hard frost.
With these steps, you’ll have healthy, blooming mums that survive Colorado’s winters and come back stronger each year. The key is starting at the right time—late May—and giving them consistent care through the growing season. Enjoy your garden!