When to Plant Basil in Idaho
The king of herbs. Basil and tomatoes are best friends in the garden and in the kitchen.
The Short Answer
Idaho Frost Dates
Your planting dates depend on which part of Idaho you're in. Here are the frost date ranges by region:
| Region | Zones | Last Frost (Spring) | First Frost (Fall) |
|---|---|---|---|
| Northern Idaho | 5a, 5b, 6a | May 5 - May 25 | Sep 15 - Oct 5 |
| Boise Area | 6b, 7a | Apr 20 - May 5 | Oct 5 - Oct 20 |
| Eastern Idaho | 3b, 4a, 4b, 5a | May 20 - Jun 10 | Sep 1 - Sep 20 |
Basil Planting Schedule for Idaho
Northern Idaho (Zones 5a, 5b, 6a)
Average last frost: May 5 - May 25 · Average first frost: Sep 15 - Oct 5
Boise Area (Zones 6b, 7a)
Average last frost: Apr 20 - May 5 · Average first frost: Oct 5 - Oct 20
Eastern Idaho (Zones 3b, 4a, 4b, 5a)
Average last frost: May 20 - Jun 10 · Average first frost: Sep 1 - Sep 20
Growing Basil in Idaho
Basil in Idaho's Climate
Basil needs warmth and dies at the first hint of frost. Start seeds indoors 6 weeks before your last frost and don't transplant until nights stay above 55°F — often 2-3 weeks after your official last frost date. Your growing window may be only 10-14 weeks, so make them count: pinch flower buds aggressively and harvest often. Consider growing in containers you can move indoors during unexpected cold snaps.
Soil Considerations for Idaho
Volcanic ash soils in south — excellent for gardening. Rocky soils in mountains. Alkaline in many areas. Make sure soil has warmed to at least 60°F before planting basil outside.
Idaho Climate & Growing Season
Arid climate. Low humidity. Hot days and cool nights. Irrigation essential. Short season at higher elevations. Basil cannot tolerate any frost, so wait until all frost danger has passed before transplanting outside. Watch local forecasts carefully in spring.
Growing season length varies across Idaho: Northern Idaho (5a, 5b, 6a) has a last frost around May 5 - May 25, while Eastern Idaho (3b, 4a, 4b, 5a) sees frost end around May 20 - Jun 10. This difference matters for basil — transplant timing shifts by several weeks across the state.
Growing Tips
Pinch off flower buds to keep leaves producing. Harvest from the top down, cutting just above a leaf pair. Succession plant for season-long supply.
Companion Planting
Plant basil alongside these companions for better growth:
Keep basil away from:
The Bottom Line
Last reviewed: March 29, 2026