Sioux City, IA Frost Dates
Average frost dates, USDA hardiness zone, and growing season length for Sioux City, Iowa.
Gardening in Sioux City
Where Iowa, Nebraska, and South Dakota meet on the Missouri River. The Loess Hills — a globally unique geological formation — provide some of the most interesting garden soil in the country.
Zone 5a with 160 frost-free days. The Missouri River bottomland and Loess Hills windblown silt soils are deep and fertile. Prairie wind exposure is significant.
The Loess Hills are one of only two places in the world with extensive loess formations (the other is China). Sioux City gardeners grow in soil that's literally been wind-delivered over millennia.
What This Means for Sioux City Gardeners
The average last spring frost in Sioux City is around April 28, and the average first fall frost arrives around October 5. That gives you approximately 160 frost-free days to work with.
At 160 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 Sioux City 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 Sioux City
Sioux City's 160-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 Iowa planting guide for all 40 plants: Iowa Planting Calendar. Or enter your zip code for exact planting dates personalized to Sioux City.
More About Zone 5A
Sioux City is in USDA Hardiness Zone 5A, which means average annual extreme minimum temperatures between -20°F to -15°F. View the full Zone 5A planting guide.
See the complete planting calendar for Iowa: Iowa Planting Calendar.
Other Cities in Iowa
Frequently Asked Questions
These dates are based on NOAA's 30-year Climate Normal data for the Sioux City 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 Sioux City (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 28) to maximize your 160-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.