When to plant Cosmos in Washington County, IL
Washington County's climate puts the Cosmos spring window between April 9 and April 30. time plantings around the expected last-frost window for best survival.
When to Plant Cosmos in Washington County, IL
Cosmos (Cosmos bipinnatus) is an airy, feathery-foliaged cottage garden annual from Mexico that thrives on neglect. It produces delicate daisy-like blooms in shades of pink, white, and magenta from midsummer until frost. Cosmos is a prolific self-sower — once established in a garden it often returns year after year without replanting. Excellent habitat plant for beneficial insects.
Washington County, Illinois is in USDA Zone 6b. The average last spring frost is April 9 and the first fall frost is October 20, giving you a growing season of approximately 194 days.
At an elevation of 1,126 feet, Washington County receives approximately 33.7 inches of rainfall annually with predominantly silt loam soil. Summer highs average 87°F, providing good warmth for Cosmos during the growing season.
Washington County Soil Profile
Soil Type
Silt Loam
Soil pH
5.9-7.2
Drainage
Well Drained
Monthly Watering Guide for Cosmos
Cosmos needs approximately 1 inches of water per week (4.3" per month). Here's how your county's rainfall compares month by month.
| Month | Cosmos Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 1.3" | 0" | ❄️ Dormant |
| Feb | — | 1.5" | 0" | ❄️ Dormant |
| Mar | — | 2.4" | 0" | ❄️ Dormant |
| Apr | 4.3" | 3.7" | 0.6" | 💧 Light watering |
| May | 4.3" | 3.4" | 0.9" | 💧 Light watering |
| Jun | 4.3" | 4.3" | 0" | ✅ Rainfall sufficient |
| Jul | 4.3" | 3.9" | 0.4" | 💧 Light watering |
| Aug | 4.3" | 3.8" | 0.5" | 💧 Light watering |
| Sep | 4.3" | 2.8" | 1.5" | 💧 Light watering |
| Oct | 4.3" | 2.5" | 1.8" | 💧 Light watering |
| Nov | — | 2.2" | 0" | ❄️ Dormant |
| Dec | — | 1.8" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Apr–Oct in Washington County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Cosmos Planting Timeline — Washington County, IL
Cosmos Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 12 | Mar 12 – Mar 26 |
| Transplant Outdoors | April 9 | Apr 9 – Apr 23 |
| Direct Sow | April 9 | Apr 9 – Apr 30 |
| Bloom | June 18 | Jun 18 – Oct 1 |
Plant 0.3" deep · 12" apart · Rows 18" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | Start Indoors |
| April | Transplant Outdoors Direct Sow |
| May | — |
| June | Bloom |
| July | Bloom |
| August | Bloom |
| September | Bloom |
| October | Bloom |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
Low — drought tolerant
📅 Days to Maturity
60–90 days
🧪 Soil pH
Needs 6–8 · Your soil: N/A
🗺️ USDA Zone
Zone 6b
📆 Growing Season
194 days in Washington County
Growing Tips for Washington County
Direct-sow after last frost; cosmos germinates readily at 65-80°F in 7-10 days. Avoid rich soil — excess fertility produces lush foliage at the expense of blooms. Cosmos tolerates poor, dry soil exceptionally well. Pinch seedlings at 8 inches to encourage branching. Self-sows freely; allow some seed heads to mature and drop for a no-fuss perennial effect in warm climates.
Companion Planting
Good Companions
Check more plant combinations with our Companion Planting Checker →
Cosmos in Other Locations
Frequently Asked Questions
When should I plant Cosmos in Washington County, IL?
Washington County is in Zone 6b with an average last frost of April 9. Plan your Cosmos planting based on this frost date — see the calendar above for exact timing.
What planting zone is Washington County, IL?
Washington County, Illinois is in USDA Hardiness Zone 6b. The average last spring frost is April 9 and first fall frost is October 20.
When should I plant Cosmos in Washington County, IL?
In Washington County, IL, plant Cosmos after the last frost (around April 9) and before the first frost (around October 20). Best results when soil holds above 50°F.
What growing zone is Washington County, IL for Cosmos?
Washington County sits in USDA Zone 6b. Cosmos grows reliably in zones 2a through 11b, so it's a good fit here.
Can Cosmos grow in Washington County's climate?
Yes — Cosmos grows well in Washington County's temperate climate. Washington County averages a 194-day frost-free season, with last frost around April 9 and first frost around October 20.
Your Washington County Garden Planner — Free
A 22-page printable planner built for Washington 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.