When to Plant Cosmos in Sublette County, WY
What to do in June
June rewards gardeners who work with the weather, not against it. Here's how to stay in step this month in Sublette County, Wyoming.
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Set out cosmos seedlings
Frost risk is low now in Sublette County, Wyoming. If you've been covering beds overnight, you can stop.
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Put cosmos seeds straight in the ground
These tolerate cool soil, so you're not gambling by sowing now.
Coming up in July — start thinking about
- Starting indoors: cosmos
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.
Sublette County, Wyoming is in USDA Zone 4b. The average last spring frost is June 22 and the first fall frost is August 24, giving you a growing season of approximately 63 days.
At an elevation of 5,005 feet, Sublette County receives approximately 22.8 inches of rainfall annually with predominantly loam soil. Summer highs average 81°F, so choose short-season varieties of Cosmos to ensure they mature before fall.
Sublette County Soil Profile
Soil Type
Loam
Soil pH
6.7-7.8
Drainage
Well Drained
Cosmos 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 Sublette County
How your county's soil matches Cosmos's growing requirements.
Soil pH
Your soil pH (6.7–7.8) is within Cosmos's preferred range (6.0–8.0).
Soil Texture
The loam soil in Sublette County is excellent for Cosmos — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is moderate (2.2%). Annual compost additions will help Cosmos.
How to Plant Cosmos
Cosmos Water Budget
Water stress score is 6/10 — consider drought-tolerant varieties and mulching
Monthly Watering Guide for Cosmos
Cosmos needs approximately 0.5 inches of water per week (2.2" per month). Here's how your county's rainfall compares month by month.
| Month | Cosmos Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 1.8" | 0" | ❄️ Dormant |
| Feb | — | 1.5" | 0" | ❄️ Dormant |
| Mar | — | 2.1" | 0" | ❄️ Dormant |
| Apr | — | 2.6" | 0" | ❄️ Dormant |
| May | — | 2.5" | 0" | ❄️ Dormant |
| Jun | 2.2" | 1.5" | 0.7" | 💧 Light watering |
| Jul | 2.2" | 2.2" | 0" | ✅ Rainfall sufficient |
| Aug | 2.2" | 2.1" | 0.1" | 💧 Light watering |
| Sep | — | 1.7" | 0" | ❄️ Dormant |
| Oct | — | 2" | 0" | ❄️ Dormant |
| Nov | — | 1.4" | 0" | ❄️ Dormant |
| Dec | — | 1.4" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Jun–Aug in Sublette County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Cosmos 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.
Cosmos Planting Timeline — Sublette County, WY
Cosmos Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | May 25 | May 25 – Jun 8 |
| Transplant Outdoors | June 29 | Jun 29 – Jul 13 |
| Direct Sow | June 29 | Jun 29 – Jul 20 |
| Bloom | September 7 | Sep 7 – Nov 30 |
Plant 0.3" deep · 12" apart · Rows 18" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | — |
| April | — |
| May | Start Indoors |
| June | Start Indoors Transplant Outdoors Direct Sow |
| July | Transplant Outdoors Direct Sow |
| August | — |
| September | Bloom |
| October | Bloom |
| November | Bloom |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
0.5"/week · Natural rainfall sufficient
📅 Days to Maturity
60–90 days
🧪 Soil pH
Needs 6–8 · Your soil: ideal
🗺️ USDA Zone
Zone 4b
📆 Growing Season
63 days in Sublette County
Growing Tips for Cosmos in Sublette County
Direct sow Cosmos outdoors after June 22 in Sublette County when soil has warmed and frost danger has passed.
Your 63.0-day growing season in Sublette County is tight for Cosmos (60.0-90.0 days to maturity). Start indoors and choose early-maturing varieties.
Common pests for Cosmos in this region include aphids and slugs. Use row covers early in the season and inspect plants weekly.
Sublette County receives only 23" of rain annually. Cosmos needs consistent moisture — install drip irrigation or water deeply 2-3 times per week.
General growing tips
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 Sublette County, WY?
Sublette County is in Zone 4b with an average last frost of June 22. Plan your Cosmos planting based on this frost date — see the calendar above for exact timing.
What planting zone is Sublette County, WY?
Sublette County, Wyoming is in USDA Hardiness Zone 4b. The average last spring frost is June 22 and first fall frost is August 24.
Your Sublette County Garden Planner — Free
A 22-page printable planner built for Sublette County (Zone 4b). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.