Boise, ID Frost Dates
Average frost dates, USDA hardiness zone, and growing season length for Boise, Idaho.
Gardening in Boise
Boise's Treasure Valley is aptly named — the rich volcanic soil and long growing season make it one of the best gardening secrets in the Pacific Northwest. While Seattle gets the headlines, Boise gardeners quietly grow tomatoes the size of softballs in conditions that combine the best of western and mountain gardening.
The Boise Valley's 168-day growing season, combined with hot summer days and cool nights (the classic high-desert pattern), produces incredibly flavorful food. The warm days drive growth; the cool nights develop sugars. Boise's volcanic-derived soil is naturally fertile and well-drained. Water comes from mountain snowmelt via an extensive irrigation network that turns high desert into garden paradise.
The city's explosive growth has brought gardeners from Portland, San Francisco, and Salt Lake, each bringing their own traditions. The Boise Farmers Market is a Saturday morning institution. The Capitol City Public Market connects garden culture with Boise's increasingly sophisticated food scene. And Idaho's famous potatoes? You can grow even better ones in your backyard.
What This Means for Boise Gardeners
The average last spring frost in Boise is around April 25, and the average first fall frost arrives around October 10. That gives you approximately 168 frost-free days to work with.
At 168 days, you're working with a compressed but productive window. Choose varieties by their days-to-maturity number — anything under 75 days is safe, 75-90 requires indoor starting, and 90+ is a calculated risk. The tradeoff: your cool, moderate summers are excellent for crops that heat-zone gardeners struggle with. Your lettuce doesn't bolt in June. Your peas produce for weeks longer. Cool-season crops are your superpower.
These dates are based on NOAA 30-year Climate Normal data for the Boise area. Your actual frost dates could shift 2-3 weeks in either direction in any given year. Learn more about our data sources.
What to Grow in Boise
Boise's 168-day season gives you plenty of time for most vegetables with good planning. Start warm-season crops indoors to maximize your window. Cool-season crops thrive in your spring and fall shoulder seasons. Recommended starting points: tomatoes, peppers, lettuce, carrots, beans, broccoli, garlic, and basil.
See the full Idaho planting guide for all 40 plants: Idaho Planting Calendar. Or enter your zip code for exact planting dates personalized to Boise.
More About Zone 6B
Boise is in USDA Hardiness Zone 6B, which means average annual extreme minimum temperatures between -5°F to 0°F. View the full Zone 6B planting guide.
See the complete planting calendar for Idaho: Idaho Planting Calendar.
Other Cities in Idaho
Frequently Asked Questions
These dates are based on NOAA's 30-year Climate Normal data for the Boise area. They represent historical averages, not predictions. In any given year, the actual last frost could be 2-3 weeks earlier or later. Microclimates within Boise (urban heat islands, hilltops, low-lying valleys) can also shift your local frost dates by a week or more.
Start warm-season seeds indoors 6-8 weeks before your last frost (April 25) to maximize your 168-day window. Direct sow cold-hardy crops like peas and lettuce 3-4 weeks before last frost. Every week of early indoor starting matters at this season length. Enter your zip code for exact dates.