When to Plant Onion in Power County, ID
May in the garden — Power County, Idaho
May rewards gardeners who work with the weather, not against it. Here's how to stay in step this month in Power County, Idaho.
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Set out onion seedlings
Frost risk is low now in Power County, Idaho. If you've been covering beds overnight, you can stop.
A few tasks this May that'll pay off in June
- Starting indoors: onion
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.
Power County, Idaho is in USDA Zone 6a. The average last spring frost is May 11 and the first fall frost is September 30, giving you a growing season of approximately 142 days.
At an elevation of 6,609 feet, Power County receives approximately 14 inches of rainfall annually with predominantly loam soil. Summer highs average 87°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.
Power County Soil Profile
Soil Type
Loam
Soil pH
6.6-8.2
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.
Soil Compatibility in Power County
How your county's soil matches Onion's growing requirements.
Soil pH
Your soil pH (6.6–8.2) is more alkaline than Onion prefers (6.0–7.0). Add sulfur or peat moss to lower pH.
Soil Texture
The loam soil in Power County is excellent for Onion — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is moderate (2.6%). Annual compost additions will help Onion.
How to Plant Onion
Fall planting: Sow 10 weeks before your first frost date for a fall harvest.
Plant Water Budget
Water stress score is 6/10 — consider drought-tolerant varieties and mulching
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" | 0" | ❄️ Dormant |
| Feb | — | 0.9" | 0" | ❄️ Dormant |
| Mar | — | 1.2" | 0" | ❄️ Dormant |
| Apr | — | 1.4" | 0" | ❄️ Dormant |
| May | 4.3" | 1.7" | 2.6" | 🚿 Regular watering |
| Jun | 4.3" | 0.9" | 3.4" | 🚿 Regular watering |
| Jul | 4.3" | 1.4" | 2.9" | 🚿 Regular watering |
| Aug | 4.3" | 1.5" | 2.8" | 🚿 Regular watering |
| Sep | 4.3" | 1.2" | 3.1" | 🚿 Regular watering |
| Oct | — | 1.3" | 0" | ❄️ Dormant |
| Nov | — | 0.8" | 0" | ❄️ Dormant |
| Dec | — | 0.8" | 0" | ❄️ Dormant |
Water needs are for active growing months only (May–Sep in Power County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Onion Heat Requirements (GDD)
What are Growing Degree Days (GDD)?
Growing Degree Days measure the total warmth your plants receive during the growing season. Think of it as a "heat bank" — every day above 50°F deposits warmth that helps your plants grow.
Each plant needs a certain amount of accumulated heat to mature. If your county provides more GDD than the plant needs, it's a great fit. If it's close, you may want to choose faster-maturing varieties or start seeds indoors to get a head start.
Onion Planting Timeline — Power County, ID
Onion Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | April 6 | Apr 6 – Apr 20 |
| Transplant Outdoors | May 11 | May 11 – May 25 |
| Direct Sow | April 27 | Apr 27 – May 18 |
| Harvest | August 10 | Aug 10 – Sep 28 |
| Fall Sowing | July 22 | Jul 22 – Aug 5 |
Plant 1" deep · 6" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | — |
| April | Start Indoors Direct Sow |
| May | Transplant Outdoors Direct Sow |
| June | — |
| July | Fall Sowing |
| August | Fall Sowing Harvest |
| September | Harvest |
| October | — |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
1"/week · 2-3 times/week
📅 Days to Maturity
90–120 days
🧪 Soil pH
Needs 6–7 · Your soil: too_alkaline
🗺️ USDA Zone
Zone 6a
📆 Growing Season
142 days in Power County
Growing Tips for Onion in Power County
Direct sow Onion outdoors after May 11 in Power County when soil has warmed and frost danger has passed.
Common pests for Onion in this region include onion maggots and thrips. Use row covers early in the season and inspect plants weekly.
Power County receives only 14" of rain annually. Onion needs consistent moisture — install drip irrigation or water deeply 2-3 times per week.
General growing tips
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 Power County, ID?
Power County is in Zone 6a with an average last frost of May 11. Plan your Onion planting based on this frost date — see the calendar above for exact timing.
What planting zone is Power County, ID?
Power County, Idaho is in USDA Hardiness Zone 6a. The average last spring frost is May 11 and first fall frost is September 30.
Your Power County Garden Planner — Free
A 24-page printable planner built for Power County (Zone 6a). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.