When to plant Onion in Phillips County, CO
Plant Onion in Phillips County after May 4; the prime window is April 20–May 11. A second sowing from July 29 to August 12 extends the harvest into fall.
When to Plant Onion in Phillips County, CO
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.
Phillips County, Colorado is in USDA Zone 5b. The average last spring frost is May 4 and the first fall frost is October 7, giving you a growing season of approximately 156 days.
At an elevation of 5,494 feet, Phillips County receives approximately 21.1 inches of rainfall annually with predominantly loam soil. Summer highs average 87°F, providing good warmth for Onion during the growing season.
Phillips County Soil Profile
Soil Type
Loam
Soil pH
6.0-7.0
Drainage
Well Drained
Onion Planting Timeline — Phillips County, CO
Onion Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 30 | Mar 30 – Apr 13 |
| Transplant Outdoors | May 4 | May 4 – May 18 |
| Direct Sow | April 20 | Apr 20 – May 11 |
| Harvest | August 3 | Aug 3 – Sep 21 |
| Fall Sowing | July 29 | Jul 29 – Aug 12 |
Plant 1" deep · 6" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | Start Indoors |
| 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
Moderate — regular watering
📅 Days to Maturity
90–120 days
🧪 Soil pH
Needs 6–7 · Your soil: N/A
🗺️ USDA Zone
Zone 5b
📆 Growing Season
156 days in Phillips County
Growing Tips for Phillips 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 Phillips County, CO?
Phillips County is in Zone 5b with an average last frost of May 4. Plan your Onion planting based on this frost date — see the calendar above for exact timing.
What planting zone is Phillips County, CO?
Phillips County, Colorado is in USDA Hardiness Zone 5b. The average last spring frost is May 4 and first fall frost is October 7.
When should I plant Onion in Phillips County, CO?
In Phillips County, CO, plant Onion after the last frost (around May 4) and before the first frost (around October 7). Best results when soil holds above 50°F.
What growing zone is Phillips County, CO for Onion?
Phillips County sits in USDA Zone 5b. Onion grows reliably in zones 3a through 10b, so it's a good fit here.
Can Onion grow in Phillips County's climate?
Yes — Onion grows well in Phillips County's temperate climate. Phillips County averages a 156-day frost-free season, with last frost around May 4 and first frost around October 7.
Your Phillips County Garden Planner — Free
A 22-page printable planner built for Phillips County (Zone 5b). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.