When to plant Onion in Ada County, ID
Aim to plant Onion in Ada County on or after April 9; the window stays open through April 30. Ada County's 176-day frost-free season gives you a single solid spring crop with a brief fall option. A second sowing from August 7 to August 21 extends the harvest into fall.
When to Plant Onion in Ada County, ID
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.
Ada County, Idaho is in USDA Zone 7a. The average last spring frost is April 23 and the first fall frost is October 16, giving you a growing season of approximately 176 days.
At an elevation of 4,372 feet, Ada County receives approximately 19.8 inches of rainfall annually with predominantly loam soil. Summer highs average 90°F, providing good warmth for Onion during the growing season. With low rainfall, drip irrigation is essential for growing Onion successfully. Mulch heavily to conserve soil moisture.
Ada County Soil Profile
Soil Type
Loam
Soil pH
6.4-7.7
Drainage
Well Drained
Monthly Watering Guide for Onion
Onion needs approximately 1 inches of water per week (4.3" per month). Here's how your county's rainfall compares month by month.
| Month | Onion Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 1.4" | 0" | ❄️ Dormant |
| Feb | — | 1.2" | 0" | ❄️ Dormant |
| Mar | — | 1.5" | 0" | ❄️ Dormant |
| Apr | 4.3" | 2" | 2.3" | 🚿 Regular watering |
| May | 4.3" | 2.4" | 1.9" | 💧 Light watering |
| Jun | 4.3" | 1.4" | 2.9" | 🚿 Regular watering |
| Jul | 4.3" | 1.8" | 2.5" | 🚿 Regular watering |
| Aug | 4.3" | 2.4" | 1.9" | 💧 Light watering |
| Sep | 4.3" | 1.5" | 2.8" | 🚿 Regular watering |
| Oct | 4.3" | 1.8" | 2.5" | 🚿 Regular watering |
| Nov | — | 1.3" | 0" | ❄️ Dormant |
| Dec | — | 1.2" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Apr–Oct in Ada County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Onion Planting Timeline — Ada County, ID
Onion Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 19 | Mar 19 – Apr 2 |
| Transplant Outdoors | April 23 | Apr 23 – May 7 |
| Direct Sow | April 9 | Apr 9 – Apr 30 |
| Harvest | July 23 | Jul 23 – Sep 10 |
| Fall Sowing | August 7 | Aug 7 – Aug 21 |
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 |
| June | — |
| July | 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
Needs 6–7 · Your soil: N/A
🗺️ USDA Zone
Zone 7a
📆 Growing Season
176 days in Ada County
Growing Tips for Ada 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
Check more plant combinations with our Companion Planting Checker →
Onion in Other Locations
Frequently Asked Questions
When should I plant Onion in Ada County, ID?
Ada County is in Zone 7a with an average last frost of April 23. Plan your Onion planting based on this frost date — see the calendar above for exact timing.
What planting zone is Ada County, ID?
Ada County, Idaho is in USDA Hardiness Zone 7a. The average last spring frost is April 23 and first fall frost is October 16.
When should I plant Onion in Ada County, ID?
In Ada County, ID, plant Onion after the last frost (around April 23) and before the first frost (around October 16). Best results when soil holds above 50°F.
What growing zone is Ada County, ID for Onion?
Ada County sits in USDA Zone 7a. Onion grows reliably in zones 3a through 10b, so it's a good fit here.
Can Onion grow in Ada County's climate?
Yes — Onion grows well in Ada County's temperate climate. Ada County averages a 176-day frost-free season, with last frost around April 23 and first frost around October 16.
Your Ada County Garden Planner — Free
A 22-page printable planner built for Ada County (Zone 7a). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.