When to Plant Watermelon in Johnson County, WY
Watermelon is a sprawling vine crop that produces sweet, juicy fruits in hot weather. Varieties range from personal-sized icebox types to 50-pound giants.
Johnson County, Wyoming is in USDA Zone 4a. The average last spring frost is May 17 and the first fall frost is September 21, giving you a growing season of approximately 127 days.
At an elevation of 8,281 feet, Johnson County receives approximately 23.7 inches of rainfall annually with predominantly loam soil. Summer highs average 81°F, so choose short-season varieties of Watermelon to ensure they mature before fall.
Johnson County Soil Profile
Soil Type
Loam
Soil pH
6.8-7.8
Drainage
Well Drained
Plant 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 Johnson County
How your county's soil matches Watermelon's growing requirements.
Soil pH
Your soil pH (6.8–7.8) overlaps with Watermelon's range (6.0–7.5), though not a perfect match.
Soil Texture
The loam soil in Johnson County is excellent for Watermelon — good drainage, moisture retention, and nutrient holding capacity.
Drainage
Drainage is adequate for Watermelon.
Organic Matter
Organic matter is moderate (2.2%). Annual compost additions will help Watermelon.
How to Plant Watermelon
Succession Planting Watermelon
Sow every 8 weeks. Last sowing by Jun 13 to harvest before frost.
Plant Water Budget
Water stress score is 6/10 — consider drought-tolerant varieties and mulching
Monthly Watering Guide for Watermelon
Watermelon 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 | Watermelon Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 1.8" | 0" | ❄️ Dormant |
| Feb | — | 1.5" | 0" | ❄️ Dormant |
| Mar | — | 1.9" | 0" | ❄️ Dormant |
| Apr | — | 2.1" | 0" | ❄️ Dormant |
| May | 6.5" | 2.8" | 3.7" | 🚿 Regular watering |
| Jun | 6.5" | 1.6" | 4.9" | 🚿 Regular watering |
| Jul | 6.5" | 2.3" | 4.2" | 🚿 Regular watering |
| Aug | 6.5" | 2.5" | 4" | 🚿 Regular watering |
| Sep | 6.5" | 2.1" | 4.4" | 🚿 Regular watering |
| Oct | — | 2.1" | 0" | ❄️ Dormant |
| Nov | — | 1.5" | 0" | ❄️ Dormant |
| Dec | — | 1.5" | 0" | ❄️ Dormant |
Water needs are for active growing months only (May–Sep in Johnson County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Watermelon 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.
Watermelon Planting Timeline — Johnson County, WY
Watermelon Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | April 5 | Apr 5 – Apr 19 |
| Transplant Outdoors | June 7 | Jun 7 – Jun 21 |
| Direct Sow | May 31 | May 31 – Jun 21 |
| Harvest | August 16 | Aug 16 – Oct 4 |
Plant 1" deep · 30" apart · Rows 42" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | — |
| April | Start Indoors |
| May | Direct Sow |
| June | Transplant Outdoors Direct Sow |
| July | — |
| August | Harvest |
| September | Harvest |
| October | Harvest |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
1.5"/week · 2-3 times/week
📅 Days to Maturity
70–100 days
🧪 Soil pH
Needs 6–7.5 · Your soil: acceptable
🗺️ USDA Zone
Zone 4a
📆 Growing Season
127 days in Johnson County
Growing Tips for Watermelon in Johnson County
Direct sow Watermelon outdoors after May 17 in Johnson County when soil has warmed and frost danger has passed.
Common pests for Watermelon in this region include squash vine borer and cucumber beetles. Use row covers early in the season and inspect plants weekly.
Johnson County receives only 24" of rain annually. Watermelon needs consistent moisture — install drip irrigation or water deeply 2-3 times per week.
General growing tips
Start seeds indoors 3-4 weeks early or direct sow after soil is warm. Plant on mounds with plenty of space. Check ripeness by looking for a yellow ground spot and dull thump when tapped.
Recommended Watermelon Varieties for Johnson County
Compact, early melons for shorter seasons
Companion Planting
Good Companions
Avoid Planting Near
Check more plant combinations with our Companion Planting Checker →
Watermelon in Other Locations
Frequently Asked Questions
When should I plant Watermelon in Johnson County, WY?
Johnson County is in Zone 4a with an average last frost of May 17. Plan your Watermelon planting based on this frost date — see the calendar above for exact timing.
What planting zone is Johnson County, WY?
Johnson County, Wyoming is in USDA Hardiness Zone 4a. The average last spring frost is May 17 and first fall frost is September 21.
Plan Your Garden with Confidence
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