Planting Guides

When to Plant Basil in Boise: Complete Guide + Best Varieties for Zone 6a

Boise, Idaho

USDA Zone 6a

Last Frost: May 5

Last updated: October 30, 2025

Learn when to plant basil in Boise with specific dates for Zone 6a. Compare 5 varieties, get timeline, discover which basil grow best in Idaho climate.

LLily Nakamura

October 30, 2025

Basil plants growing successfully in Boise Idaho garden with mountain foothills backdrop — — Image © PlantReference.org 2026

Quick Answer

Start basil seeds indoors March 15-30 in Boise. Transplant outdoors May 10-20 after soil reaches 60°F consistently. Choose heat-tolerant varieties for Zone 6a success.

TL;DR

Plant basil in Boise after May 5th when soil temperatures reach 60°F consistently. Start seeds indoors March 15-30, transplant outdoors May 10-20 for 158-day growing season. Genovese and Thai varieties perform best in Zone 6a conditions with proper heat accumulation.

Frequently Asked Questions

When is it safe to plant basil outside in Boise?

Plant basil outdoors in Boise after May 10th when soil temperatures consistently reach 60°F. While our average last frost is May 5th, cold soil damages basil more than air temperature. Check soil temperature daily and wait for consistent warmth. Cold snaps can occur through mid-May, so monitor weather forecasts closely.

Which basil varieties perform best in Boise's hot summers?

Ocimum basilicum 'Thai' and Ocimum basilicum 'Genovese' perform exceptionally well in Boise's Zone 6a climate. Thai basil handles extreme heat best, thriving in 95°F+ temperatures. Genovese produces excellent yields with afternoon shade protection. Avoid delicate varieties like Lemon basil unless you can provide consistent moisture and protection from intense heat.

Can I direct sow basil seeds in Boise?

Limited direct sowing is possible in Boise, but timing is critical. Sow seeds May 20-June 1 when soil reaches 65°F consistently. Choose fast-maturing varieties like Lemon basil (60-75 days) for best results. Starting transplants indoors remains more reliable for our short growing season, ensuring full harvest before October frost.

How do I prevent my basil from bolting in Boise's heat?

Prevent bolting by providing afternoon shade during July-August when temperatures exceed 90°F. Maintain consistent soil moisture with drip irrigation or soaker hoses. Pinch flower buds immediately when they appear. Choose slow-bolt varieties and plant succession crops every 3-4 weeks for continuous harvest throughout the season.

What soil amendments work best for basil in Boise?

Amend Boise's alkaline clay soils with 2-3 inches of compost annually to improve drainage and lower pH toward basil's preferred 6.0-7.0 range. Avoid quick-fix pH adjusters that can damage soil biology. Organic matter from compost provides slow pH buffering while improving water retention in our arid climate.

How late can I plant basil for fall harvest in Boise?

Plant final basil crops by June 15th for fall harvest before our October 10th first frost. Choose 60-day varieties and provide row cover protection for extending season. Late plantings often outperform heat-stressed early crops during September's ideal growing conditions.

Should I grow basil in containers or ground in Boise?

Both methods work well in Boise, each with advantages. Containers allow moving plants for optimal sun/shade balance throughout the season and protect from soil temperature fluctuations. Ground planting in raised beds provides more root space and consistent moisture. Choose containers for purple basil requiring maximum light control.

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Tagged with

#basil planting #Boise gardening #Zone 6a herbs #Idaho vegetable gardening #herb growing #basil varieties #spring planting #frost dates #container herbs #succession planting

Written By

Lily Nakamura

Lily is a Master Gardener and high-desert homesteader outside Boise. She and her husband moved to Idaho from the Bay Area and had to completely relearn gardening for a climate with alkaline soil, intense sun, hard freezes, and limited water. Lily now grows a large vegetable garden, maintains a small orchard of cold-hardy fruit trees, and raises cut flowers for the local farmers market. She writes about the specific challenges of intermountain gardening—short seasons, temperature swings, and the importance of soil amendment in high-pH soils. Lily is honest about the learning curve: high-desert gardening is humbling, and she thinks more gardening writers should admit when conditions are genuinely difficult.