Growing Dahlias in Colorado: Planting, Soil,Watering & Climate Guide for Front Range + Western Slope Gardeners
When to Plant Dahlias in Colorado
Colorado gardeners are largely defined by frost dates, not just USDA zone maps.
Front Range frost windows:
Avg. last frost: May 8–15
- Safe planting date: Mid–Late May
- First blooms: August
- Peak production: August–October
Western Slope (Grand Junction + surrounding valleys):
- Warmer + longer season
- Planting can begin: Early May
- Higher heat tolerance + strong performance
Dahlias are not frost-hardy — plant too early and cold soil can delay or stunt growth.
Rule of thumb:
Plant in May → Enjoy blooms August–October.
Colorado Soil: Heavy Clay, Amending, & Drainage
One of the biggest differentiators for Colorado growers is soil structure, especially along the Front Range where heavy clay is common.
Clay soils:
✔ Warm slowly
✔ Drain poorly (risking rot if overwatered early)
✔ Get concrete-hard in mid-summer heat
Strategies to improve performance:
- Add compost + coarse organic matter
- Avoid peat-only mixes (can compact + repel water when dry)
- Use raised beds or mounded rows for drainage
- Don’t over-amend with sand (can create brick-like layers)
Dahlias perform extremely well in:
✔ loose, friable soil
✔ compost-rich beds
Western Slope soils tend to be warmer, sandier and lower in organic content — compost additions still help but drainage is rarely the constraint.
Watering Dahlias in Colorado
Watering is where many Colorado gardeners struggle — especially with drip systems in clay soil.
Starter rule for tubers (no foliage yet):
- Water sparingly until sprouted
- Moist but not wet soil
- Overwatering pre-sprout is the #1 cause of rot
Once foliage is established:
- 2x per week early summer
- 3x per week mid-summer (heat + wind)
- Increase frequency during hot/dry wind events
For drip systems:
- Aim for 45 minutes per session
- Clay soils may need longer intervals, not shorter
Check soil 6–8” down — if it’s wet or cold, reduce frequency; if dry mid-day, increased
Heat, Sun, & Shade Cloth
Staking & Wind Support
Most dahlias reach 4–5ft+ by August and require support.
Front Range winds make staking essential, not optional.
Options:
- T-posts + Hortonova netting
- Wooden stakes + twine corral
- Metal cages (smaller plantings)
Without support, plants can:
- snap mid-season
- flop onto neighbors
- ruin wedding-quality stems
Support early—don’t wait until they’re 4 ft tall.
Insects & Pests in Colorado Dahlias
-
Japanese Beetles
- Active mid-summer
- Target blooms + foliage
- Manual removal & traps are effective
- Avoid spraying blooms (reduces pollination + Worse in drought years
-
Earwigs
- Hide inside blooms
- Create cosmetic damage - oval holes
- Baiting + strategic trap placement works well
-
Grasshoppers
- Damage foliage + ragged petal edges
- Barrier fabrics + garden perimeter treatments help
Cutting Dahlias for Long Stems
-
Cut flower stems deeply
One of the reasons Colorado gardeners fall in love with dahlias is their incredible beauty, variety, and colors. To get florist-quality stems great for bouquets and flower arrangements - the key technique is cutting deeply.
Deep cuts:
✔ encourage stronger future stems
✔ create longer usable stems for arrangements
✔ signal the plant to branch low, improving airflow and production
How to cut:
• Use clean snips
• Follow the stem down 2–3 nodes (where leaves form)
• Cut above a pair of outward-facing leaves
This encourages new branching from lower nodes, not just the top.
-
Disbudding
Disbudding means removing smaller side buds and leaving a single main bud to bloom.
Benefits of disbudding:
✔ larger blooms (especially dinnerplates)
✔ longer stems
✔ more uniform presentation (important for weddings/photography)
Disbudding is optional for most backyard gardeners, but wedding florists, collectors, and show growers use it to maximize bloom quality.
When to disbud:
- Do it when buds are still small and easy to pinch
- Focus on varieties where bloom size or presentation matters (e.g., Cafe au Lait, Break Out, Cornel Bronze for show stems)
Digging, Dividing & Storing Dahlia Tubers in Colorado
-
When to dig
After the first killing frost:
- Wait 7-14 days for the tubers to firm up and the eyes to swell up
- Label the variety with flagging tape
- Cut stems down to ~6 inches
- Dig up the tubers carefully
-
Washing & dividing
Why divide quickly in Colorado
Colorado’s low humidity can desiccate tubers rapidly. Most Front Range and Western Slope growers:✔ dig
✔ wash
✔ divide
✔ and store within 1–3 days.
This prevents shriveling and loss of viability.
Washing & dividing
- Wash soil off gently with a hose (don’t pressure-wash eyes off)
- Divide using a sharp knife or snips
- Include at least 1 eye per tuber
-
Storage method for Colorado climates
Because the air is dry, tubers need moisture buffering.
A reliable Colorado method:
✔ Pack in lightly moistened vermiculite or peat moss
✔ Store in plastic totes with a lid (helps prevent desiccation)
✔ Keep at ~45°F
Monitoring in storage
Check tubers monthly:
- Remove any that look soft or moldy
- If shriveling, mist lightly (only the medium, not directly onto tubers)
Spring wake-up
Bring totes up to 55–60°F before planting time to “wake” tubers.
Popular Dahlia Forms - dahlias come in dozens of forms
-
Ball Dahlias
✔ round, tight petals
✔ long vase life
✔ strong stems (great for wind)
✔ excellent for cutting gardens
Popular varieties:
-
Dinnerplate Dahlias
✔ large, dramatic blooms (8–12”)
✔ showstoppers for weddings + photos
Popular varieties:- Cafe au Lait (bridal favorite)
- Break Out (peachy blush, elegant)
Dinnerplates benefit more from staking due to bloom size, head weight, & wind.
