When to plant Phlox in Black Hawk County, IA
The best window to plant Phlox in Black Hawk County, is May 13–June 3, when soil warms to 50°F. Last frost typically hits April 29; first frost October 7.
When to Plant Phlox in Black Hawk County, IA
Garden Phlox (Phlox paniculata) is a beloved native perennial of eastern North America, producing large, domed clusters of fragrant flowers atop upright stems from mid-summer into fall. Its sweet honey-like fragrance carries on summer evenings and draws hummingbirds, butterflies, and sphinx moths. Modern cultivars offer colors spanning white, pink, salmon, red, purple, and bicolors. A classic cottage garden stalwart, phlox combines well with black-eyed Susans, echinacea, and ornamental grasses in naturalistic plantings. Select mildew-resistant cultivars for best long-term performance.
Black Hawk County, Iowa is in USDA Zone 5a. The average last spring frost is April 29 and the first fall frost is October 7, giving you a growing season of approximately 161 days.
At an elevation of 1,380 feet, Black Hawk County receives approximately 38.3 inches of rainfall annually with predominantly silt loam soil. Summer highs average 84°F, so choose short-season varieties of Phlox to ensure they mature before fall.
Black Hawk County Soil Profile
Soil Type
Silt Loam
Soil pH
6.0-7.0
Drainage
Well Drained
Phlox Planting Timeline — Black Hawk County, IA
Phlox Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | February 25 | Feb 25 – Mar 11 |
| Transplant Outdoors | May 13 | May 13 – May 27 |
| Direct Sow | May 13 | May 13 – Jun 3 |
| Bloom | July 29 | Jul 29 – Oct 14 |
Plant 0.3" deep · 18" apart · Rows 24" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | Start Indoors |
| March | Start Indoors |
| April | — |
| May | Transplant Outdoors Direct Sow |
| June | Direct Sow |
| July | Bloom |
| August | Bloom |
| September | Bloom |
| October | Bloom |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
Moderate — regular watering
📅 Days to Maturity
80–110 days
🧪 Soil pH
Needs 6–7 · Your soil: N/A
🗺️ USDA Zone
Zone 5a
📆 Growing Season
161 days in Black Hawk County
Growing Tips for Black Hawk County
Start seeds indoors 8–10 weeks before last frost, or transplant container divisions in spring. Named cultivar seeds may not come true; divisions from named plants are the preferred propagation method. Space generously (18–24 inches) and avoid overhead watering to reduce powdery mildew risk. Good air circulation is critical — thin clumps to the strongest 5–7 stems per plant in spring. Deadhead after the primary bloom flush to encourage secondary flowering. Division every 2–3 years in spring keeps plants vigorous. Fall planting of divisions (Zones 5+) is equally effective. Year 2+ plants develop into full clumps with the most prolific bloom.
Companion Planting
Good Companions
Check more plant combinations with our Companion Planting Checker →
Phlox in Other Locations
Frequently Asked Questions
When should I plant Phlox in Black Hawk County, IA?
Black Hawk County is in Zone 5a with an average last frost of April 29. Plan your Phlox planting based on this frost date — see the calendar above for exact timing.
What planting zone is Black Hawk County, IA?
Black Hawk County, Iowa is in USDA Hardiness Zone 5a. The average last spring frost is April 29 and first fall frost is October 7.
When should I plant Phlox in Black Hawk County, IA?
In Black Hawk County, IA, plant Phlox after the last frost (around April 29) and before the first frost (around October 7). Best results when soil holds above 50°F.
What growing zone is Black Hawk County, IA for Phlox?
Black Hawk County sits in USDA Zone 5a. Phlox grows reliably in zones 3a through 9a, so it's a good fit here.
Can Phlox grow in Black Hawk County's climate?
Yes — Phlox grows well in Black Hawk County's temperate climate. Black Hawk County averages a 161-day frost-free season, with last frost around April 29 and first frost around October 7.
Your Black Hawk County Garden Planner — Free
A 22-page printable planner built for Black Hawk County (Zone 5a). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.