When to Plant Basil in Jefferson County, MT
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, Montana is in USDA Zone 4b. The average last spring frost is June 15 and the first fall frost is September 7, giving you a growing season of approximately 84 days.
At an elevation of 7,214 feet, Jefferson County receives approximately 21.5 inches of rainfall annually with predominantly loam soil. Summer highs average 82°F, so choose short-season varieties of Basil to ensure they mature before fall.
Jefferson County Soil Profile
Soil Type
Loam
Soil pH
6.4-7.9
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 Jefferson County
How your county's soil matches Basil's growing requirements.
Soil pH
Your soil pH (6.4–7.9) 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.
Drainage
Drainage is adequate for Basil.
Organic Matter
Organic matter is moderate (2.5%). Annual compost additions will help Basil.
How to Plant Basil
Plant 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 | — | 1.5" | 0" | ❄️ Dormant |
| Feb | — | 1.4" | 0" | ❄️ Dormant |
| Mar | — | 2" | 0" | ❄️ Dormant |
| Apr | — | 2" | 0" | ❄️ Dormant |
| May | — | 2.5" | 0" | ❄️ Dormant |
| Jun | 2.6" | 1.5" | 1.1" | 💧 Light watering |
| Jul | 2.6" | 2" | 0.6" | 💧 Light watering |
| Aug | 2.6" | 2" | 0.6" | 💧 Light watering |
| Sep | 2.6" | 2" | 0.6" | 💧 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 (Jun–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, MT
Basil Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | April 20 | Apr 20 – May 4 |
| Transplant Outdoors | July 6 | Jul 6 – Jul 20 |
| Direct Sow | June 22 | Jun 22 – Jul 13 |
| Harvest | August 31 | Aug 31 – Nov 2 |
Plant 0.5" deep · 8" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | — |
| April | Start Indoors |
| May | Start Indoors |
| June | Direct Sow |
| July | Transplant Outdoors Direct Sow |
| August | Harvest |
| September | Harvest |
| October | Harvest |
| November | Harvest |
| 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 4b
📆 Growing Season
84 days in Jefferson County
Growing Tips for Basil in Jefferson County
Direct sow Basil outdoors after June 15 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, MT?
Jefferson County is in Zone 4b with an average last frost of June 15. Plan your Basil planting based on this frost date — see the calendar above for exact timing.
What planting zone is Jefferson County, MT?
Jefferson County, Montana is in USDA Hardiness Zone 4b. The average last spring frost is June 15 and first fall frost is September 7.
Plan Your Garden with Confidence
Get our free Garden Planner — designed to help Jefferson County gardeners in Zone 4b organize planting dates, track what's growing, and never miss a planting window.
Get Your Free Garden Planner →Free download. Plan your entire garden season in minutes.