When to Plant Onion in Miami-Dade County, FL
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.
Miami-Dade County, Florida is in USDA Zone 10b. The average last spring frost is January 1 and the first fall frost is December 31, giving you a growing season of approximately 364 days.
At an elevation of 123 feet, Miami-Dade County receives approximately 58.7 inches of rainfall annually with predominantly sand soil. Summer highs average 90°F, providing good warmth for Onion during the growing season. Sandy soil warms quickly in spring — great for early planting — but Onion will need more frequent watering and organic matter to retain nutrients. Ample rainfall means less supplemental watering, but ensure good drainage to prevent Onion root diseases.
Miami-Dade County Soil Profile
Soil Type
Sand
Soil pH
5.1-6.3
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 Miami-Dade County
How your county's soil matches Onion's growing requirements.
Soil pH
Your soil pH (5.1–6.3) is more acidic than Onion prefers (6.0–7.0). Add garden lime to raise pH.
Soil Texture
Sandy soil in Miami-Dade 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 (1.3%). Add 2-3 inches of compost before planting Onion.
How to Plant Onion
Fall planting: Sow 8 weeks before your first frost date for a fall harvest.
Plant Water Budget
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 | 4.3" | 2.9" | 1.4" | 💧 Light watering |
| Feb | 4.3" | 2.9" | 1.4" | 💧 Light watering |
| Mar | 4.3" | 3.4" | 0.9" | 💧 Light watering |
| Apr | 4.3" | 2.5" | 1.8" | 💧 Light watering |
| May | 4.3" | 3.8" | 0.5" | 💧 Light watering |
| Jun | 4.3" | 8.1" | 0" | ✅ Rainfall sufficient |
| Jul | 4.3" | 9.5" | 0" | ✅ Rainfall sufficient |
| Aug | 4.3" | 8.6" | 0" | ✅ Rainfall sufficient |
| Sep | 4.3" | 7.1" | 0" | ✅ Rainfall sufficient |
| Oct | 4.3" | 5" | 0" | ✅ Rainfall sufficient |
| Nov | 4.3" | 2.3" | 2" | 💧 Light watering |
| Dec | 4.3" | 2.7" | 1.6" | 💧 Light watering |
Water needs are for active growing months only (Jan–Dec in Miami-Dade 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 — Miami-Dade County, FL
Onion Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | December 4 | Dec 4 – Dec 18 |
| Transplant Outdoors | January 1 | Jan 1 – Jan 15 |
| Direct Sow | December 11 | Dec 11 – Jan 1 |
| Harvest | April 2 | Apr 2 – May 21 |
| Fall Sowing | November 5 | Nov 5 – Nov 19 |
Plant 1" deep · 6" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | Transplant Outdoors Direct Sow |
| February | — |
| March | — |
| April | Harvest |
| May | Harvest |
| June | — |
| July | — |
| August | — |
| September | — |
| October | — |
| November | Fall Sowing |
| December | Start Indoors Direct Sow |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
1"/week · 1-2 times/week
📅 Days to Maturity
90–120 days
🧪 Soil pH
Needs 6–7 · Your soil: too_acidic
🗺️ USDA Zone
Zone 10b
📆 Growing Season
364 days in Miami-Dade County
Growing Tips for Onion in Miami-Dade County
Sandy soil in Miami-Dade County dries quickly — mulch Onion with 2-3 inches of straw and water deeply 2-3 times per week rather than lightly every day.
Common pests for Onion in this region include onion maggots and thrips. Use row covers early in the season and inspect plants weekly.
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 Miami-Dade County, FL?
Miami-Dade County is in Zone 10b with an average last frost of January 1. Plan your Onion planting based on this frost date — see the calendar above for exact timing.
What planting zone is Miami-Dade County, FL?
Miami-Dade County, Florida is in USDA Hardiness Zone 10b. The average last spring frost is January 1 and first fall frost is December 31.
Plan Your Garden with Confidence
Get our free Garden Planner — designed to help Miami-Dade County gardeners in Zone 10b 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.