When to Plant Onion in Cochise County, AZ
Your May gardening checklist
We've pulled the most time-sensitive tasks for Cochise County, Arizona this May and put them front and centre. Tackle them in order.
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Time to start onion inside
Starting these indoors now means sturdy transplants ready the moment your soil warms up.
To set up a strong June, finish these tasks
- First harvests: 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.
Cochise County, Arizona is in USDA Zone 8b. The average last spring frost is March 30 and the first fall frost is November 9, giving you a growing season of approximately 224 days.
At an elevation of 3,447 feet, Cochise County receives approximately 9.4 inches of rainfall annually with predominantly sandy loam soil. Summer highs average 105°F, so Onion may need afternoon shade and extra watering during peak heat. Sandy soil warms quickly in spring — great for early planting — but Onion will need more frequent watering and organic matter to retain nutrients. With low rainfall, drip irrigation is essential for growing Onion successfully. Mulch heavily to conserve soil moisture.
Cochise County Soil Profile
Soil Type
Sandy Loam
Soil pH
6.9-8.3
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 Cochise County
How your county's soil matches Onion's growing requirements.
Soil pH
Your soil pH (6.9–8.3) is more alkaline than Onion prefers (6.0–7.0). Add sulfur or peat moss to lower pH.
Soil Texture
Sandy soil in Cochise County warms quickly in spring but drains fast. Onion will need more frequent watering and regular compost additions to retain nutrients.
Drainage
Drainage is adequate for Onion.
Organic Matter
Organic matter is low (0.8%). Add 2-3 inches of compost before planting 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 | — | 0.6" | 0" | ❄️ Dormant |
| Feb | — | 0.5" | 0" | ❄️ Dormant |
| Mar | 4.3" | 0.5" | 3.8" | 🚿 Regular watering |
| Apr | 4.3" | 0.3" | 4" | 🚿 Regular watering |
| May | 4.3" | 0.2" | 4.1" | 🚿 Regular watering |
| Jun | 4.3" | 0.3" | 4" | 🚿 Regular watering |
| Jul | 4.3" | 1.6" | 2.7" | 🚿 Regular watering |
| Aug | 4.3" | 1.8" | 2.5" | 🚿 Regular watering |
| Sep | 4.3" | 1.4" | 2.9" | 🚿 Regular watering |
| Oct | 4.3" | 0.9" | 3.4" | 🚿 Regular watering |
| Nov | 4.3" | 0.5" | 3.8" | 🚿 Regular watering |
| Dec | — | 0.7" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Mar–Nov in Cochise 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 — Cochise County, AZ
Onion Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | February 23 | Feb 23 – Mar 9 |
| Transplant Outdoors | March 30 | Mar 30 – Apr 13 |
| Direct Sow | March 16 | Mar 16 – Apr 6 |
| Harvest | June 29 | Jun 29 – Aug 17 |
| Fall Sowing | August 31 | Aug 31 – Sep 14 |
Plant 1" deep · 6" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | Start Indoors |
| March | Start Indoors Transplant Outdoors Direct Sow |
| April | Transplant Outdoors Direct Sow |
| May | — |
| June | Harvest |
| July | Harvest |
| August | Fall Sowing Harvest |
| September | Fall Sowing |
| 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 8b
📆 Growing Season
224 days in Cochise County
Growing Tips for Onion in Cochise County
Direct sow Onion outdoors after March 30 in Cochise County when soil has warmed and frost danger has passed.
Sandy soil in Cochise County dries quickly — mulch Onion with 2-3 inches of straw and water deeply 2-3 times per week rather than lightly every day.
With summer highs reaching 105°F in Cochise County, provide afternoon shade for Onion and water deeply in the morning.
Common pests for Onion in this region include onion maggots and thrips. Use row covers early in the season and inspect plants weekly.
Cochise County receives only 9" 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
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Onion in Other Locations
Frequently Asked Questions
When should I plant Onion in Cochise County, AZ?
Cochise County is in Zone 8b with an average last frost of March 30. Plan your Onion planting based on this frost date — see the calendar above for exact timing.
What planting zone is Cochise County, AZ?
Cochise County, Arizona is in USDA Hardiness Zone 8b. The average last spring frost is March 30 and first fall frost is November 9.
Your Cochise County Garden Planner — Free
A 24-page printable planner built for Cochise County (Zone 8b). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.