š§ When to Plant Onion in USDA Zone 9b (2026 Guide)
Long season. Start from seed indoors very early or use sets. Here is the cool-season planting schedule for onion in zone 9b (covering areas like Orlando FL, Tucson AZ). All dates are based on 2026 frost data for your zone.
Start Seeds Indoors
Dec 2
Transplant
Jan 13
Harvest From
Apr 23
Because onion is a cool-season crop, it tolerates light frost and can go out around Jan 13, before zone 9b's average last frost on Feb 10.
- Type: Cool-season
- Method: Transplant
- Days to harvest: 100
- Spacing: 4" apart
- Sun: Full sun
- Zone 9b frost: Feb 10 ā Dec 15
- Season length: ~308 days
- Companions: carrot, lettuce, beets
Growing onion in zone 9b
Zone 9b has an average last spring frost around Feb 10 and a first fall frost around Dec 15, giving roughly 308 frost-free growing days. That window comfortably fits onion's 100-day cycle, with room for a second succession planting if you time it right.
Get a head start by sowing seeds indoors around Dec 2, roughly 10 weeks before your last frost. Move the seedlings outside around Jan 13. Give each plant about 4 inches of space in full sun.
Zone 9b specific growing notes
In zone 9b (Orlando FL, Tucson AZ), your 308-day growing season means onion should be one of your first spring plantings. Cool-season crops thrive in the mild part of your growing window. Monitor soil temperature ā onion germinates best when soil is 40-75Ā°F.
Your first fall frost around Dec 15 means your last possible harvest is roughly late Dec. For a continuous supply, consider succession planting every 2-3 weeks from Jan 13 through mid-season.
Pro tip for onion
Day-length determines bulb formationāplant long-day varieties north of 37Ā°N latitude and short-day varieties south of it. Using the wrong type means you will get scallions, not bulbs.
Troubleshooting onion
Onion maggots tunnel into bulbs from below causing rot. The adult fly lays eggs at the base of seedlings. Rotate allium family crops (onions, garlic, leeks) on a 3-year cycle to break the pest cycle.
Growing onion in containers
Grow 4-6 bulbs per 5-gallon bucket, spaced evenly. Green onions (scallions) are even easierāplant sets 1 inch apart in any 6-inch deep container and harvest continuously.
Can you plant onion twice a year?
Generally noāonions are a single long-season crop taking 100-120 days. However, you can interplant fast crops like radishes or lettuce between young onion rows before they fill out.
Frequently asked questions
When should I plant onion in zone 9b?
Transplant around Jan 13. If starting from seed indoors, sow around Dec 2. Because onion is a cool-season crop, it tolerates light frost and can go out around Jan 13, before zone 9b's average last frost on Feb 10.
How long does onion take to grow in zone 9b?
About 100 days from transplanting to first harvest. A Jan 13 planting in zone 9b is typically ready to pick from around Apr 23. Zone 9b has about 308 frost-free days ā plenty of time for a second succession planting.
How far apart should I space onion?
Space onion about 4 inches apart in full sun. This gives each plant enough room for roots to spread and leaves to catch sunlight without competing.
What is the best tip for growing onion?
Day-length determines bulb formationāplant long-day varieties north of 37Ā°N latitude and short-day varieties south of it. Using the wrong type means you will get scallions, not bulbs.
What are common problems with onion and how do I fix them?
Onion maggots tunnel into bulbs from below causing rot. The adult fly lays eggs at the base of seedlings. Rotate allium family crops (onions, garlic, leeks) on a 3-year cycle to break the pest cycle.
Can I grow onion in a container?
Grow 4-6 bulbs per 5-gallon bucket, spaced evenly. Green onions (scallions) are even easierāplant sets 1 inch apart in any 6-inch deep container and harvest continuously.
Can I plant a second crop of onion for fall harvest?
Generally noāonions are a single long-season crop taking 100-120 days. However, you can interplant fast crops like radishes or lettuce between young onion rows before they fill out.
What grows well next to onion?
Good companion plants for onion are carrot, lettuce, beets. Avoid planting near warm-season crops that compete for space and nutrients. Onion also benefits from crop rotation ā do not plant it in the same spot year after year.