When to Plant Astilbe in Kittitas County, WA
July in the garden — Kittitas County, Washington
Each item below is timed to Kittitas County, Washington's frost dates and soil temperatures. Skip nothing, stress about nothing.
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Indoor seed-starting week for astilbe
Give them 6–8 weeks indoors before the last frost and you'll transplant into warm soil with seedlings that are already leaping.
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Collect astilbe at their peak
This is the payoff month. Bring a basket, bring a friend, and get into the beds.
Looking ahead to August
- 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.
Kittitas County, Washington is in USDA Zone 7a. The average last spring frost is May 7 and the first fall frost is October 2, giving you a growing season of approximately 148 days.
At an elevation of 2,468 feet, Kittitas County receives approximately 18.9 inches of rainfall annually with predominantly silt loam soil. Summer highs average 90°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.
Kittitas County Soil Profile
Soil Type
Silt Loam
Soil pH
5.5-6.7
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 Kittitas County
How your county's soil matches Astilbe's growing requirements.
Soil pH
Your soil pH (5.5–6.7) overlaps with Astilbe's range (6.0–8.0), though not a perfect match.
Soil Texture
The silt loam soil in Kittitas County is excellent for Astilbe — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is excellent (4.4%) — Astilbe will thrive.
How to Plant Astilbe
Succession Planting Astilbe
Sow every 8 weeks. Last sowing by Jun 24 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 | — | 2.9" | 0" | ❄️ Dormant |
| Feb | — | 2" | 0" | ❄️ Dormant |
| Mar | — | 1.8" | 0" | ❄️ Dormant |
| Apr | — | 1.7" | 0" | ❄️ Dormant |
| May | 6.5" | 1.2" | 5.3" | 🚿 Regular watering |
| Jun | 6.5" | 0.8" | 5.7" | 🚿 Regular watering |
| Jul | 6.5" | 0.3" | 6.2" | 🚿 Regular watering |
| Aug | 6.5" | 0.4" | 6.1" | 🚿 Regular watering |
| Sep | 6.5" | 0.8" | 5.7" | 🚿 Regular watering |
| Oct | 6.5" | 1.7" | 4.8" | 🚿 Regular watering |
| Nov | — | 2.8" | 0" | ❄️ Dormant |
| Dec | — | 2.6" | 0" | ❄️ Dormant |
Water needs are for active growing months only (May–Oct in Kittitas 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 — Kittitas County, WA
Astilbe Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 5 | Mar 5 – Mar 19 |
| Transplant Outdoors | May 14 | May 14 – May 28 |
| Bloom | July 23 | Jul 23 – Sep 17 |
Plant 1.5" deep · 18" apart · Rows 24" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| 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: acceptable
🗺️ USDA Zone
Zone 7a
📆 Growing Season
148 days in Kittitas County
Growing Tips for Astilbe in Kittitas County
Direct sow Astilbe outdoors after May 07 in Kittitas County when soil has warmed and frost danger has passed.
Kittitas County receives only 19" 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 Kittitas County, WA?
Kittitas County is in Zone 7a with an average last frost of May 7. Plan your Astilbe planting based on this frost date — see the calendar above for exact timing.
What planting zone is Kittitas County, WA?
Kittitas County, Washington is in USDA Hardiness Zone 7a. The average last spring frost is May 7 and first fall frost is October 2.
Your Kittitas County Garden Planner — Free
A 22-page printable planner built for Kittitas County (Zone 7a). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.