When to plant Hydrangeas in St. Louis County, MO
St. Louis County's 194-day season only supports one Hydrangeas planting per year. Sow between April 20 and May 4 for the best chance at full maturity before October 24.
When to Plant Hydrangeas in St. Louis County, MO
Hydrangeas (Hydrangea spp.) are among the most spectacular summer-blooming shrubs, with large mophead, lacecap, or panicle flower clusters lasting weeks in the garden and drying beautifully for arrangements. Native to Asia and North America alike, the genus spans several garden species with different hardiness and blooming habits. Panicle hydrangeas (H. paniculata, e.g., Limelight) are the most cold-hardy (Zone 3) and most reliable bloomers; smooth hydrangeas (H. arborescens, e.g., Annabelle) are equally tough. Bigleaf hydrangeas (H. macrophylla) are prized for blue/pink color-shifting blooms but require reliable snow cover or winter protection in Zones 5–6. Flower color in macrophylla types is determined by soil pH (acidic = blue, alkaline = pink).
St. Louis County, Missouri is in USDA Zone 7a. The average last spring frost is April 13 and the first fall frost is October 24, giving you a growing season of approximately 194 days.
At an elevation of 895 feet, St. Louis County receives approximately 40.1 inches of rainfall annually with predominantly silt loam soil. Summer highs average 86°F, providing good warmth for Hydrangeas during the growing season.
St. Louis County Soil Profile
Soil Type
Silt Loam
Soil pH
6.0-7.0
Drainage
Well Drained
Hydrangeas Planting Timeline — St. Louis County, MO
Hydrangeas Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | February 2 | Feb 2 – Feb 16 |
| Transplant Outdoors | April 20 | Apr 20 – May 4 |
| Bloom | June 29 | Jun 29 – Oct 19 |
Plant 1" deep · 48" apart · Rows 60" 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 | Bloom |
| October | Bloom |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Partial Shade (3-6 hours)
💧 Water
Moderate — regular watering
📅 Days to Maturity
90–150 days
🧪 Soil pH
Needs 5.5–6.5 · Your soil: N/A
🗺️ USDA Zone
Zone 7a
📆 Growing Season
194 days in St. Louis County
Growing Tips for St. Louis County
Plant container-grown specimens in spring or fall, spacing at least 3–5 feet apart to allow for mature shrub spread. Most hydrangeas prefer morning sun with afternoon shade, especially in Zones 7+. Keep consistently moist — the name derives from the Greek for water vessel. Prune panicle and smooth types in late winter/early spring (they bloom on new wood). Prune bigleaf types only lightly after bloom; cutting stems in fall removes next year's buds. In Zone 5–6, protect bigleaf varieties with burlap or wire cages filled with leaves over winter. Fall planting (Zones 5+) gives excellent root establishment before summer heat. Year 2+ plants reach full size and bloom.
Companion Planting
Good Companions
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Hydrangeas in Other Locations
Frequently Asked Questions
When should I plant Hydrangeas in St. Louis County, MO?
St. Louis County is in Zone 7a with an average last frost of April 13. Plan your Hydrangeas planting based on this frost date — see the calendar above for exact timing.
What planting zone is St. Louis County, MO?
St. Louis County, Missouri is in USDA Hardiness Zone 7a. The average last spring frost is April 13 and first fall frost is October 24.
When should I plant Hydrangeas in St. Louis County, MO?
In St. Louis County, MO, plant Hydrangeas after the last frost (around April 13) and before the first frost (around October 24). Best results when soil holds above 50°F.
What growing zone is St. Louis County, MO for Hydrangeas?
St. Louis County sits in USDA Zone 7a. Hydrangeas grows reliably in zones 3a through 9a, so it's a good fit here.
Can Hydrangeas grow in St. Louis County's climate?
Yes — Hydrangeas grows well in St. Louis County's temperate climate. St. Louis County averages a 194-day frost-free season, with last frost around April 13 and first frost around October 24.
Your St. Louis County Garden Planner — Free
A 22-page printable planner built for St. Louis 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.