š§ When to Plant Onion in USDA Zone 7a (2026 Guide)
Long season. Start from seed indoors very early or use sets. Here is the cool-season planting schedule for onion in zone 7a (covering areas like Nashville TN, Oklahoma City OK). All dates are based on 2026 frost data for your zone.
Start Seeds Indoors
Jan 30
Transplant
Mar 13
Harvest From
Jun 21
Because onion is a cool-season crop, it tolerates light frost and can go out around Mar 13, before zone 7a's average last frost on Apr 10.
- Type: Cool-season
- Method: Transplant
- Days to harvest: 100
- Spacing: 4" apart
- Sun: Full sun
- Zone 7a frost: Apr 10 ā Oct 25
- Season length: ~198 days
- Companions: carrot, lettuce, beets
Growing onion in zone 7a
Zone 7a has an average last spring frost around Apr 10 and a first fall frost around Oct 25, giving roughly 198 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 Jan 30, roughly 10 weeks before your last frost. Move the seedlings outside around Mar 13. Give each plant about 4 inches of space in full sun.
Zone 7a specific growing notes
In zone 7a (Nashville TN, Oklahoma City OK), your 198-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 Oct 25 means your last possible harvest is roughly late Oct. For a continuous supply, consider succession planting every 2-3 weeks from Mar 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 7a?
Transplant around Mar 13. If starting from seed indoors, sow around Jan 30. Because onion is a cool-season crop, it tolerates light frost and can go out around Mar 13, before zone 7a's average last frost on Apr 10.
How long does onion take to grow in zone 7a?
About 100 days from transplanting to first harvest. A Mar 13 planting in zone 7a is typically ready to pick from around Jun 21. Zone 7a has about 198 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.