When to Plant Basil in Washington County, CO
Basil is a fragrant warm-season herb essential to Italian and Thai cuisines. It comes in many varieties including sweet, Thai, purple, and lemon types.
Washington County, Colorado is in USDA Zone 5a. The average last spring frost is May 10 and the first fall frost is October 5, giving you a growing season of approximately 148 days.
At an elevation of 6,091 feet, Washington County receives approximately 13 inches of rainfall annually with predominantly loam soil. Summer highs average 85°F, providing good warmth for Basil during the growing season. With low rainfall, drip irrigation is essential for growing Basil successfully. Mulch heavily to conserve soil moisture.
Washington County Soil Profile
Soil Type
Loam
Soil pH
6.8-8.3
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.
Plant Water Budget
Water stress score is 10/10 — consider drought-tolerant varieties and mulching
Basil Planting Timeline — Washington County, CO
Basil Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 22 | Mar 22 – Apr 5 |
| Transplant Outdoors | May 24 | May 24 – Jun 7 |
| Direct Sow | May 17 | May 17 – Jun 7 |
| Harvest | July 19 | Jul 19 – Sep 20 |
Plant 0.5" deep · 8" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | Start Indoors |
| April | Start Indoors |
| May | Transplant Outdoors Direct Sow |
| June | Transplant Outdoors Direct Sow |
| July | Harvest |
| August | Harvest |
| September | Harvest |
| October | — |
| November | — |
| December | — |
Growing Conditions
Sun
Full Sun (6-8+ hours)
Water
Moderate — regular watering
Days to Maturity
50–75 days
Soil pH
6 – 7
USDA Zone
Zone 5a
Growing Season
148 days
Growing Tips for Washington County
Start seeds indoors or direct sow after last frost. Pinch flower buds to extend leaf production. Harvest leaves from the top down, cutting just above a leaf pair.
Companion Planting
Good Companions
Avoid Planting Near
Level Up Your Garden
Isolate 150 ft between varieties. Different basil species can cross.
Basil in Other Locations
Frequently Asked Questions
When should I plant Basil in Washington County, CO?
Washington County is in Zone 5a with an average last frost of May 10. Plan your Basil planting based on this frost date — see the calendar above for exact timing.
What planting zone is Washington County, CO?
Washington County, Colorado is in USDA Hardiness Zone 5a. The average last spring frost is May 10 and first fall frost is October 5.
Plan Your Garden with Confidence
Get our free Garden Planner — designed to help Washington County gardeners in Zone 5a organize planting dates, track what's growing, and never miss a planting window.
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