When to plant Astilbe in Bonner County, ID
Bonner County sits in cold Zone 6b. Plant Astilbe May 12–May 26 for the single annual harvest; the October 3 first frost closes the window.
When to Plant Astilbe in Bonner County, ID
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.
Bonner County, Idaho is in USDA Zone 6b. The average last spring frost is May 5 and the first fall frost is October 3, giving you a growing season of approximately 151 days.
At an elevation of 7,480 feet, Bonner County receives approximately 12.9 inches of rainfall annually with predominantly loam soil. Summer highs average 86°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.
Bonner County Soil Profile
Soil Type
Loam
Soil pH
6.0-7.0
Drainage
Well Drained
Astilbe Planting Timeline — Bonner County, ID
Astilbe Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 3 | Mar 3 – Mar 17 |
| Transplant Outdoors | May 12 | May 12 – May 26 |
| Bloom | July 21 | Jul 21 – Sep 29 |
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
High — keep soil consistently moist
📅 Days to Maturity
70–100 days
🧪 Soil pH
Needs 6–8 · Your soil: N/A
🗺️ USDA Zone
Zone 6b
📆 Growing Season
151 days in Bonner County
Growing Tips for Bonner County
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 Bonner County, ID?
Bonner County is in Zone 6b with an average last frost of May 5. Plan your Astilbe planting based on this frost date — see the calendar above for exact timing.
What planting zone is Bonner County, ID?
Bonner County, Idaho is in USDA Hardiness Zone 6b. The average last spring frost is May 5 and first fall frost is October 3.
When should I plant Astilbe in Bonner County, ID?
In Bonner County, ID, plant Astilbe after the last frost (around May 5) and before the first frost (around October 3). Best results when soil holds above 50°F.
What growing zone is Bonner County, ID for Astilbe?
Bonner 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 Bonner County's climate?
Yes — Astilbe grows well in Bonner County's temperate climate. Bonner County averages a 151-day frost-free season, with last frost around May 5 and first frost around October 3.
Your Bonner County Garden Planner — Free
A 22-page printable planner built for Bonner 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.