When to Plant Onion in Boone County, IA
Onions are a fundamental kitchen staple available in yellow, white, and red varieties. Choose long-day, short-day, or intermediate types based on your latitude.
Boone County, Iowa is in USDA Zone 5a. The average last spring frost is April 28 and the first fall frost is October 6, giving you a growing season of approximately 161 days.
At an elevation of 950 feet, Boone County receives approximately 30.7 inches of rainfall annually with predominantly silt loam soil. Summer highs average 85°F, providing good warmth for Onion during the growing season.
Boone County Soil Profile
Soil Type
Silt Loam
Soil pH
6.1-6.9
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.
Plant Water Budget
Water stress score is 6/10 — consider drought-tolerant varieties and mulching
Onion Planting Timeline — Boone County, IA
Onion Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 24 | Mar 24 – Apr 7 |
| Transplant Outdoors | April 28 | Apr 28 – May 12 |
| Direct Sow | April 14 | Apr 14 – May 5 |
| Fall Sowing | July 28 | Jul 28 – Aug 11 |
| Harvest | July 28 | Jul 28 – Sep 15 |
Plant 1" deep · 6" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | Start Indoors |
| April | Start Indoors Transplant Outdoors Direct Sow |
| May | Transplant Outdoors Direct Sow |
| June | — |
| July | Fall Sowing Harvest |
| August | Fall Sowing Harvest |
| September | Harvest |
| October | — |
| November | — |
| December | — |
Growing Conditions
Sun
Full Sun (6-8+ hours)
Water
Moderate — regular watering
Days to Maturity
90–120 days
Soil pH
6 – 7
USDA Zone
Zone 5a
Growing Season
161 days
Growing Tips for Boone County
Start seeds indoors 8-10 weeks before transplanting. Match day-length type to your latitude. Stop watering when tops begin to fall over and cure bulbs for 2-3 weeks before storage.
Companion Planting
Good Companions
Avoid Planting Near
Level Up Your Garden
Onion in Other Locations
Frequently Asked Questions
When should I plant Onion in Boone County, IA?
Boone County is in Zone 5a with an average last frost of April 28. Plan your Onion planting based on this frost date — see the calendar above for exact timing.
What planting zone is Boone County, IA?
Boone County, Iowa is in USDA Hardiness Zone 5a. The average last spring frost is April 28 and first fall frost is October 6.
Plan Your Garden with Confidence
Get our free Garden Planner — designed to help Boone County gardeners in Zone 5a organize planting dates, track what's growing, and never miss a planting window.
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