When to plant Astilbe in Union County, GA
Plant Astilbe in Union County, between April 18 and May 2 — the only viable window. Zone 7b's short season (195 frost-free days) rules out a fall crop.
When to Plant Astilbe in Union County, GA
Your July game plan for Union County, Georgia
If you only do a handful of things in the garden this July, make it these. They're sequenced around your zone's frost timing.
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Bring in the astilbe
The more you pick, the more the plant produces. Letting fruit overripen tells the plant it's time to stop.
Get ahead of 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.
Union County, Georgia is in USDA Zone 7b. The average last spring frost is April 11 and the first fall frost is October 23, giving you a growing season of approximately 195 days.
At an elevation of 175 feet, Union County receives approximately 61.4 inches of rainfall annually with predominantly clay loam soil. Summer highs average 93°F, providing good warmth for Astilbe during the growing season. Clay soil retains moisture well for Astilbe, but amend with compost to improve drainage and prevent root rot. Ample rainfall means less supplemental watering, but ensure good drainage to prevent Astilbe root diseases.
Union County Soil Profile
Soil Type
Clay Loam
Soil pH
5.8-6.2
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 Union County
How your county's soil matches Astilbe's growing requirements.
Soil pH
Your soil pH (5.8–6.2) overlaps with Astilbe's range (6.0–8.0), though not a perfect match.
Soil Texture
The clay loam soil in Union County is excellent for Astilbe — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is moderate (2.7%). Annual compost additions will help Astilbe.
How to Plant Astilbe
Succession Planting Astilbe
Sow every 8 weeks. Last sowing by Jul 15 to harvest before frost.
Astilbe Water Budget
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 | — | 6" | 0" | ❄️ Dormant |
| Feb | — | 4.6" | 0" | ❄️ Dormant |
| Mar | — | 5.8" | 0" | ❄️ Dormant |
| Apr | 6.5" | 4.5" | 2" | 💧 Light watering |
| May | 6.5" | 5.3" | 1.2" | 💧 Light watering |
| Jun | 6.5" | 5.1" | 1.4" | 💧 Light watering |
| Jul | 6.5" | 5.7" | 0.8" | 💧 Light watering |
| Aug | 6.5" | 6.2" | 0.3" | 💧 Light watering |
| Sep | 6.5" | 4.8" | 1.7" | 💧 Light watering |
| Oct | 6.5" | 3.6" | 2.9" | 💧 Light watering |
| Nov | — | 4.2" | 0" | ❄️ Dormant |
| Dec | — | 5.6" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Apr–Oct in Union 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 — Union County, GA
Astilbe Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | February 7 | Feb 7 – Feb 21 |
| Transplant Outdoors | April 18 | Apr 18 – May 2 |
| Bloom | June 27 | Jun 27 – Aug 22 |
Plant 1.5" deep · 18" apart · Rows 24" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | Start Indoors |
| March | — |
| April | Transplant Outdoors |
| May | Transplant Outdoors |
| June | Bloom |
| July | Bloom |
| August | Bloom |
| September | — |
| October | — |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Partial Shade (3-6 hours)
💧 Water
1.5"/week · Only during dry spells
📅 Days to Maturity
70–100 days
🧪 Soil pH
Needs 6–8 · Your soil: acceptable
🗺️ USDA Zone
Zone 7b
📆 Growing Season
195 days in Union County
Growing Tips for Astilbe in Union County
Direct sow Astilbe outdoors after April 11 in Union County when soil has warmed and frost danger has passed.
With Union County's clay soil (28% clay), work in 3-4 inches of compost before planting Astilbe. Avoid tilling when soil is wet to prevent compaction.
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 Union County, GA?
Union County is in Zone 7b with an average last frost of April 11. Plan your Astilbe planting based on this frost date — see the calendar above for exact timing.
What planting zone is Union County, GA?
Union County, Georgia is in USDA Hardiness Zone 7b. The average last spring frost is April 11 and first fall frost is October 23.
When should I plant Astilbe in Union County, GA?
In Union County, GA, plant Astilbe after the last frost (around April 11) and before the first frost (around October 23). Best results when soil holds above 50°F.
What growing zone is Union County, GA for Astilbe?
Union County sits in USDA Zone 7b. Astilbe grows reliably in zones 3a through 8b, so it's a good fit here.
Can Astilbe grow in Union County's climate?
Yes — Astilbe grows well in Union County's temperate climate. Union County averages a 195-day frost-free season, with last frost around April 11 and first frost around October 23.
Your Union County Garden Planner — Free
A 22-page printable planner built for Union County (Zone 7b). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.