If you want a spectacular fall display in your Colorado garden, timing is everything. Knowing exactly when to plant mums in Colorado is the key to success against our unique climate challenges. Our dramatic temperature swings, intense sun, and unpredictable early snows can make gardening tricky. But with the right schedule, your mums will thrive and provide that iconic burst of autumn color.
When to Plant Mums in Colorado
This is the golden rule for Colorado gardeners: plant mums in the spring. Aim for after your last average frost date, when the soil is workable and warming up. For most of the Front Range, this is from mid-May to early June. In higher elevations, you may need to wait until early June or even late June.
Spring planting is non-negotiable here. It gives the plant’s roots all summer to establish a strong, deep system. A mum with a robust root structure is far more likely to survive its first winter and return as a hardy perennial. Fall-planted mums, often bought in full bloom from garden centers, simply don’t have enough time to anchor themselves before the ground freezes.
Why Spring Planting is a Must
Colorado’s climate presents specific hurdles for mums, also called chrysanthemums. Our conditions include:
- Rapid Temperature Drops: We can go from a warm fall day to a hard freeze overnight. A spring-planted mum is better equipped to handle this shock.
- Dry Air & Intense Sun: Strong roots can access deeper soil moisture, preventing the plant from drying out and scorching.
- Poor Winter Survival: The number one reason mums fail here is being planted too late. They are often treated as annuals, but with proper timing, they can be lovely perennials.
Choosing the Right Mums for Colorado
Not all mums are created equal, especially for our climate. Look for varieties labeled as “hardy garden mums” or “Minnesota mums,” as these are bred for colder zones. Some reliable types for Colorado include:
- ‘Sheffield’
- ‘Cambodian Queen’
- ‘Venus’
- ‘Maiden’s Blush’
- ‘Apricot Courtier’
When you shop, avoid the compact, gift-style mums if you want a perennial. Instead, seek out mums from local nurseries in the spring; they will stock varieties suited to our area.
The Step-by-Step Planting Guide
Once you have your hardy mums and the spring weather has settled, follow these steps.
1. Select the Perfect Spot
Mums need full sun in Colorado—at least 6 hours of direct light. Morning sun is especially beneficial. They also require excellent drainage. If your soil is heavy clay (common here), you must amend it. Avoid low spots where water collects or cold air settles.
2. Prepare the Soil
Our native soil often needs help. Work in 3 to 4 inches of compost or well-rotted manure into the top 8-12 inches of soil. This improves drainage, adds nutrients, and helps retain some moisture. A slightly acidic to neutral pH is best.
3. Planting Correctly
Dig a hole twice as wide as the root ball but no deeper. Gently loosen the roots if they are pot-bound. Place the plant in the hole so the top of the root ball is level with the soil surface. Backfill with your amended soil and pat it down gently to remove air pockets.
4. Watering and Initial Care
Water deeply immediately after planting. Continue to water regularly, keeping the soil consistently moist (but not soggy) for the first few weeks as the plant establishes. A 2-inch layer of mulch around the base will help conserve moisture and regulate soil temperature.
Seasonal Care for Colorado Mums
Your job isn’t done after planting. Ongoing care through the year ensures healthy plants and better blooms.
Spring and Summer Care
- Pinching: This is crucial for bushy, bloom-heavy plants. Starting in late spring, when shoots are about 6 inches tall, use your fingers to pinch off the top inch of each stem. Repeat this every 2-3 weeks until about the 4th of July. Then stop to allow flower buds to form.
- Watering: Mums have shallow roots. Water deeply when the top inch of soil feels dry, especially during our hot, dry summer spells.
- Fertilizing: Feed with a balanced, all-purpose fertilizer in early summer. You can switch to a fertilizer higher in phosphorus (the middle number) as bud begin to form in late summer.
Fall and Winter Care
- Enjoy the Blooms: Deadhead spent flowers to encourage more blooms until the show is over.
- Do NOT Cut Back in Fall: Leave the dead foliage and stems standing over winter. They provide crucial insulation for the crown of the plant.
- Winter Mulching: After the ground has frozen hard (usually late November or December), apply a thick, loose layer of straw or shredded leaves over the plant. This protects it from freeze-thaw cycles. Do not use heavy, matting mulch.
- Spring Cleanup: In early spring, once you see new green growth at the base, you can carefully cut away the old, dead stems from the previous year.
Troubleshooting Common Problems
Even with the best care, issues can arise. Here’s how to handle common Colorado mum troubles.
- Leggy, Floppy Growth: Usually means not enough sun or not enough pinching in spring. Ensure a full sun location and be diligent with your pinching schedule next year.
- Few or No Blooms: Likely caused by too much shade, over-fertilizing with nitrogen (which promotes leaves, not flowers), or pinching back too late in the summer.
- Winter Die-Off: If a spring-planted mum doesn’t return, it’s often due to a lack of winter mulch, poor drainage causing the crown to rot, or an exceptionally severe winter. Try a different, hardier variety.
- Pests: Watch for aphids and spider mites, especially in hot weather. A strong spray of water from the hose is often enough to dislodge them.
FAQ: Mums in Colorado
Can I plant potted mums in the fall?
You can, but treat them as annuals. Their chance of surviving the winter is very low because the root system won’t establish in time. For a permanent garden fixture, always plant in spring.
What are the best mums for high altitude gardens?
Stick with the hardiest varieties mentioned earlier. Focus on improving soil drainage even more and providing winter mulch without fail. Planting on a slight slope can also help with cold air drainage.
How often should I water mums in Denver’s climate?
There’s no set schedule. Check the soil! During the hot, windy summer, you might need to water 2-3 times a week. In cooler spring and fall weather, once a week may be plenty. Always water at the base, not the foliage.
Should I divide my mums?
Yes, dividing every 2-3 years in the spring keeps them vigorous and prevents the center from dying out. Simply dig up the clump, use a sharp shovel or knife to cut it into smaller sections (each with roots and shoots), and replant immediately.
Getting the timing right makes all the difference for Colorado gardeners. By choosing hardy mums and planting them in the spring, you give them the best possible start. With some attentive pinching, careful watering, and thoughtful winter protection, you can enjoy these vibrant fall flowers for many seasons to come. The effort is well worth it when your garden is glowing with color against the backdrop of our blue autumn skies.