When to plant Astilbe in Delta County, CO
Delta County's short 160-day growing season means one Astilbe planting between May 8 and May 22. No fall crop in Zone 6b.
When to Plant Astilbe in Delta County, CO
June in the garden — Delta County, Colorado
A quick June briefing for Delta County, Colorado gardeners — what's urgent, what's next, and what can wait.
To set up a strong July, finish these tasks
- Starting indoors: astilbe
- First harvests: astilbe
Astilbe (Astilbe x arendsii) is a premier perennial for shaded, moist gardens, producing feathery plume-like flower spikes in shades of pink, red, white, and lavender above deeply cut, ferny foliage. Originating in Asia and naturalized in shade gardens worldwide, astilbe thrives where many sun-lovers fail: under trees, beside water features, or in persistently moist woodland borders. The dried flower plumes remain attractive through fall and winter. Different cultivars extend the bloom season from early summer through early fall when several varieties are combined.
Delta County, Colorado is in USDA Zone 6b. The average last spring frost is May 1 and the first fall frost is October 8, giving you a growing season of approximately 160 days.
At an elevation of 4,470 feet, Delta County receives approximately 13.4 inches of rainfall annually with predominantly loam soil. Summer highs average 87°F, providing good warmth for Astilbe during the growing season. With low rainfall, drip irrigation is essential for growing Astilbe successfully. Mulch heavily to conserve soil moisture.
Delta County Soil Profile
Soil Type
Loam
Soil pH
6.7-7.8
Drainage
Well Drained
Astilbe Planting Risk Windows
Percentages indicate frost risk at transplant. The 70% safe window means there is a 30% chance of frost after transplant — suitable for cold-hardy crops or gardeners with frost protection. The 90% safe window is best for tender plants.
Soil Compatibility in Delta County
How your county's soil matches Astilbe's growing requirements.
Soil pH
Your soil pH (6.7–7.8) is within Astilbe's preferred range (6.0–8.0).
Soil Texture
The loam soil in Delta County is excellent for Astilbe — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is moderate (2.2%). Annual compost additions will help Astilbe.
How to Plant Astilbe
Succession Planting Astilbe
Sow every 8 weeks. Last sowing by Jun 30 to harvest before frost.
Astilbe Water Budget
Water stress score is 6/10 — consider drought-tolerant varieties and mulching
Monthly Watering Guide for Astilbe
Astilbe needs approximately 1.5 inches of water per week (6.5" per month). Here's how your county's rainfall compares month by month.
| Month | Astilbe Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 1" | 0" | ❄️ Dormant |
| Feb | — | 0.7" | 0" | ❄️ Dormant |
| Mar | — | 1.2" | 0" | ❄️ Dormant |
| Apr | — | 1.4" | 0" | ❄️ Dormant |
| May | 6.5" | 1.4" | 5.1" | 🚿 Regular watering |
| Jun | 6.5" | 0.9" | 5.6" | 🚿 Regular watering |
| Jul | 6.5" | 1.3" | 5.2" | 🚿 Regular watering |
| Aug | 6.5" | 1.4" | 5.1" | 🚿 Regular watering |
| Sep | 6.5" | 1.1" | 5.4" | 🚿 Regular watering |
| Oct | 6.5" | 1.1" | 5.4" | 🚿 Regular watering |
| Nov | — | 1.1" | 0" | ❄️ Dormant |
| Dec | — | 0.8" | 0" | ❄️ Dormant |
Water needs are for active growing months only (May–Oct in Delta County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Astilbe Heat Requirements (GDD)
What are Growing Degree Days (GDD)?
Growing Degree Days measure the total warmth your plants receive during the growing season. Think of it as a "heat bank" — every day above 50°F deposits warmth that helps your plants grow.
Each plant needs a certain amount of accumulated heat to mature. If your county provides more GDD than the plant needs, it's a great fit. If it's close, you may want to choose faster-maturing varieties or start seeds indoors to get a head start.
Astilbe Planting Timeline — Delta County, CO
Astilbe Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | February 27 | Feb 27 – Mar 13 |
| Transplant Outdoors | May 8 | May 8 – May 22 |
| Bloom | July 17 | Jul 17 – Sep 25 |
Plant 1.5" deep · 18" apart · Rows 24" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | Start Indoors |
| March | Start Indoors |
| April | — |
| May | Transplant Outdoors |
| June | — |
| July | Bloom |
| August | Bloom |
| September | Bloom |
| October | — |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Partial Shade (3-6 hours)
💧 Water
1.5"/week · 2-3 times/week
📅 Days to Maturity
70–100 days
🧪 Soil pH
Needs 6–8 · Your soil: ideal
🗺️ USDA Zone
Zone 6b
📆 Growing Season
160 days in Delta County
Growing Tips for Astilbe in Delta County
Direct sow Astilbe outdoors after May 01 in Delta County when soil has warmed and frost danger has passed.
Delta County receives only 13" of rain annually. Astilbe needs consistent moisture — install drip irrigation or water deeply 2-3 times per week.
General growing tips
Plant bare-root crowns in spring as soon as the ground is workable, setting eyes 1–2 inches below soil level. Fall planting (Zones 4+) is equally effective. Consistent moisture is non-negotiable — astilbe will wilt and scorch in drought. Amend with generous compost to improve moisture retention. Partial shade (morning sun, afternoon shade) is ideal; deep shade reduces bloom but foliage remains. Fertilize lightly in spring with a balanced slow-release granular. Divide every 3–5 years in early spring as clumps become congested. Leave plumes standing through winter for ornamental interest and wildlife value. Year 2+ plants produce the fullest bloom spikes; first-year crowns may flower lightly or not at all.
Companion Planting
Good Companions
Check more plant combinations with our Companion Planting Checker →
Astilbe in Other Locations
Frequently Asked Questions
When should I plant Astilbe in Delta County, CO?
Delta County is in Zone 6b with an average last frost of May 1. Plan your Astilbe planting based on this frost date — see the calendar above for exact timing.
What planting zone is Delta County, CO?
Delta County, Colorado is in USDA Hardiness Zone 6b. The average last spring frost is May 1 and first fall frost is October 8.
When should I plant Astilbe in Delta County, CO?
In Delta County, CO, plant Astilbe after the last frost (around May 1) and before the first frost (around October 8). Best results when soil holds above 50°F.
What growing zone is Delta County, CO for Astilbe?
Delta County sits in USDA Zone 6b. Astilbe grows reliably in zones 3a through 8b, so it's a good fit here.
Can Astilbe grow in Delta County's climate?
Yes — Astilbe grows well in Delta County's temperate climate. Delta County averages a 160-day frost-free season, with last frost around May 1 and first frost around October 8.
Your Delta County Garden Planner — Free
A 22-page printable planner built for Delta County (Zone 6b). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.