When to Plant Onion in Teller 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.
Teller County, Colorado is in USDA Zone 5a. The average last spring frost is May 11 and the first fall frost is October 6, giving you a growing season of approximately 148 days.
At an elevation of 6,538 feet, Teller County receives approximately 19.5 inches of rainfall annually with predominantly loam soil. Summer highs average 84°F, so choose short-season varieties of Onion to ensure they mature before fall. With low rainfall, drip irrigation is essential for growing Onion successfully. Mulch heavily to conserve soil moisture.
Teller County Soil Profile
Soil Type
Loam
Soil pH
6.4-8.1
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 — Teller County, CO
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 |
| Fall Sowing | July 28 | Jul 28 – Aug 11 |
| Harvest | August 10 | Aug 10 – Sep 28 |
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
Moderate — regular watering
Days to Maturity
90–120 days
Soil pH
6 – 7
USDA Zone
Zone 5a
Growing Season
148 days
Growing Tips for Teller 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 Teller County, CO?
Teller County is in Zone 5a 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 Teller County, CO?
Teller County, Colorado is in USDA Hardiness Zone 5a. The average last spring frost is May 11 and first fall frost is October 6.
Plan Your Garden with Confidence
Get our free Garden Planner — designed to help Teller County gardeners in Zone 5a organize planting dates, track what's growing, and never miss a planting window.
Get Your Free Garden Planner →Free download. Plan your entire garden season in minutes.