When to plant Basil in Jefferson County, CO
In Jefferson County, Basil is a spring-only crop. Plant May 21–June 11 once soil hits 50°F.
When to Plant Basil in Jefferson County, CO
Top priorities for Jefferson County, Colorado gardeners in July
Here's what deserves your attention in Jefferson County, Colorado this month. Everything below is tailored to Zone 6a and timed around your local frost dates.
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Start basil indoors
You're about 11 weeks out from your last frost — the perfect window to get these germinating indoors.
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Collect basil at their peak
This is the payoff month. Bring a basket, bring a friend, and get into the beds.
Coming up in August — start thinking about
- First harvests: basil
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.
Jefferson County, Colorado is in USDA Zone 6a. The average last spring frost is May 14 and the first fall frost is September 26, giving you a growing season of approximately 135 days.
At an elevation of 5,376 feet, Jefferson County receives approximately 22.7 inches of rainfall annually with predominantly loam soil. Summer highs average 84°F, so choose short-season varieties of Basil to ensure they mature before fall.
Jefferson County Soil Profile
Soil Type
Loam
Soil pH
6.8-7.7
Drainage
Well Drained
Basil 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 Jefferson County
How your county's soil matches Basil's growing requirements.
Soil pH
Your soil pH (6.8–7.7) is more alkaline than Basil prefers (6.0–7.0). Add sulfur or peat moss to lower pH.
Soil Texture
The loam soil in Jefferson County is excellent for Basil — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is moderate (2.6%). Annual compost additions will help Basil.
How to Plant Basil
Succession Planting Basil
Sow every 5.7 weeks. Last sowing by Jul 13 to harvest before frost.
Basil Water Budget
Water stress score is 8/10 — consider drought-tolerant varieties and mulching
Monthly Watering Guide for Basil
Basil needs approximately 0.6 inches of water per week (2.6" per month). Here's how your county's rainfall compares month by month.
| Month | Basil Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 1.8" | 0" | ❄️ Dormant |
| Feb | — | 1.3" | 0" | ❄️ Dormant |
| Mar | — | 1.9" | 0" | ❄️ Dormant |
| Apr | — | 2.7" | 0" | ❄️ Dormant |
| May | 2.6" | 2.6" | 0" | ✅ Rainfall sufficient |
| Jun | 2.6" | 1.8" | 0.8" | 💧 Light watering |
| Jul | 2.6" | 1.9" | 0.7" | 💧 Light watering |
| Aug | 2.6" | 2.4" | 0.2" | 💧 Light watering |
| Sep | 2.6" | 1.7" | 0.9" | 💧 Light watering |
| Oct | — | 1.8" | 0" | ❄️ Dormant |
| Nov | — | 1.4" | 0" | ❄️ Dormant |
| Dec | — | 1.4" | 0" | ❄️ Dormant |
Water needs are for active growing months only (May–Sep in Jefferson County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Basil 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.
Basil Planting Timeline — Jefferson County, CO
Basil Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 26 | Mar 26 – Apr 9 |
| Transplant Outdoors | May 28 | May 28 – Jun 11 |
| Direct Sow | May 21 | May 21 – Jun 11 |
| Harvest | July 23 | Jul 23 – Sep 24 |
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
0.6"/week · Natural rainfall sufficient
📅 Days to Maturity
50–75 days
🧪 Soil pH
Needs 6–7 · Your soil: too_alkaline
🗺️ USDA Zone
Zone 6a
📆 Growing Season
135 days in Jefferson County
Growing Tips for Basil in Jefferson County
Direct sow Basil outdoors after May 14 in Jefferson County when soil has warmed and frost danger has passed.
General growing tips
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
Check more plant combinations with our Companion Planting Checker →
Isolate 150 ft between varieties. Different basil species can cross.
Basil in Other Locations
Frequently Asked Questions
When should I plant Basil in Jefferson County, CO?
Jefferson County is in Zone 6a with an average last frost of May 14. Plan your Basil planting based on this frost date — see the calendar above for exact timing.
What planting zone is Jefferson County, CO?
Jefferson County, Colorado is in USDA Hardiness Zone 6a. The average last spring frost is May 14 and first fall frost is September 26.
When should I plant Basil in Jefferson County, CO?
In Jefferson County, CO, plant Basil after the last frost (around May 14) and before the first frost (around September 26). Best results when soil holds above 50°F.
What growing zone is Jefferson County, CO for Basil?
Jefferson County sits in USDA Zone 6a. Basil grows reliably in zones 4a through 11b, so it's a good fit here.
Can Basil grow in Jefferson County's climate?
Yes — Basil grows well in Jefferson County's temperate climate. Jefferson County averages a 135-day frost-free season, with last frost around May 14 and first frost around September 26.
Your Jefferson County Garden Planner — Free
A 22-page printable planner built for Jefferson County (Zone 6a). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.