When to Plant Onion in Cache County, UT
Your May game plan for Cache County, Utah
Welcome to May in Zone 6a. These are the moves that will have the biggest impact on your growing season.
-
Direct-sow onion
Mark the row. Birds and stray feet both have opinions about unmarked beds.
Coming up in June — start thinking about
- Transplants going out: onion
- Fall sowing: 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.
Cache County, Utah is in USDA Zone 6a. The average last spring frost is June 11 and the first fall frost is September 2, giving you a growing season of approximately 83 days.
At an elevation of 6,265 feet, Cache County receives approximately 15.5 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.
Cache County Soil Profile
Soil Type
Loam
Soil pH
6.6-8.4
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 Cache County
How your county's soil matches Onion's growing requirements.
Soil pH
Your soil pH (6.6–8.4) is more alkaline than Onion prefers (6.0–7.0). Add sulfur or peat moss to lower pH.
Soil Texture
The loam soil in Cache County is excellent for Onion — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is moderate (2.3%). 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 10/10 — 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 | — | 1.1" | 0" | ❄️ Dormant |
| Feb | — | 0.9" | 0" | ❄️ Dormant |
| Mar | — | 1.3" | 0" | ❄️ Dormant |
| Apr | — | 1.7" | 0" | ❄️ Dormant |
| May | — | 2" | 0" | ❄️ Dormant |
| Jun | 4.3" | 1.1" | 3.2" | 🚿 Regular watering |
| Jul | 4.3" | 1.3" | 3" | 🚿 Regular watering |
| Aug | 4.3" | 1.5" | 2.8" | 🚿 Regular watering |
| Sep | 4.3" | 1.3" | 3" | 🚿 Regular watering |
| Oct | — | 1.4" | 0" | ❄️ Dormant |
| Nov | — | 1.1" | 0" | ❄️ Dormant |
| Dec | — | 0.8" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Jun–Sep in Cache 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 — Cache County, UT
Onion Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | May 7 | May 7 – May 21 |
| Transplant Outdoors | June 11 | Jun 11 – Jun 25 |
| Direct Sow | May 28 | May 28 – Jun 18 |
| Harvest | September 10 | Sep 10 – Oct 29 |
| Fall Sowing | June 24 | Jun 24 – Jul 8 |
Plant 1" deep · 6" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | — |
| April | — |
| May | Start Indoors Direct Sow |
| June | Transplant Outdoors Direct Sow Fall Sowing |
| July | Fall Sowing |
| August | — |
| September | Harvest |
| October | Harvest |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
1"/week · Only during dry spells
📅 Days to Maturity
90–120 days
🧪 Soil pH
Needs 6–7 · Your soil: too_alkaline
🗺️ USDA Zone
Zone 6a
📆 Growing Season
83 days in Cache County
Growing Tips for Onion in Cache County
Direct sow Onion outdoors after June 11 in Cache County when soil has warmed and frost danger has passed.
Your 83.0-day growing season in Cache County is tight for Onion (90.0-120.0 days to maturity). Start indoors and choose early-maturing varieties.
Common pests for Onion in this region include onion maggots and thrips. Use row covers early in the season and inspect plants weekly.
Cache County receives only 16" 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 Cache County, UT?
Cache County is in Zone 6a with an average last frost of June 11. Plan your Onion planting based on this frost date — see the calendar above for exact timing.
What planting zone is Cache County, UT?
Cache County, Utah is in USDA Hardiness Zone 6a. The average last spring frost is June 11 and first fall frost is September 2.
Your Cache County Garden Planner — Free
A 24-page printable planner built for Cache 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.