Onion at a glance
| Botanical name | Allium cepa |
|---|---|
| Family | Amaryllidaceae |
| Other names | bulb onion |
| Plant type | Vegetable; biennial grown as an annual |
| Size | 1 to 1.5 feet tall |
| Light | Full sun (6 or more hours of direct sun) |
| Water | Water evenly; onions have shallow roots. |
| Soil | Loose, well-drained, fertile soil. |
| USDA hardiness zones | Grown as a cool-season crop in every zone; choose long-day, intermediate or short-day types for your area. |
| USDA PLANTS symbol | ALCE |
When to plant onion
Plant sets or transplants outdoors 2 to 4 weeks before your average last spring frost. From seed, start indoors 8 to 10 weeks before transplanting.
Turn these into real dates for your area with the planting calendar.
How to grow onion
- Pick a variety bred for your region's day length.
- Plant sets or transplants shallowly in early spring.
- Keep weeds down; onions compete poorly.
- Water evenly and stop when tops start to fall over.
- Harvest when most tops have fallen, then dry them for a few weeks in a dry, airy place.
Water and soil
Water: Water evenly; onions have shallow roots.
Soil: Loose, well-drained, fertile soil.
Light: Full sun (6 or more hours of direct sun).
Common problems
- Bolting (flower stalks)
- Often from large sets or cold spells. Use small sets and harvest bolted onions first.
- Thrips
- Silvery streaks on leaves in hot, dry weather.
Is onion safe for cats and dogs?
Toxic
Toxic
The ASPCA lists Onion (Allium cepa) as toxic to cats and toxic to dogs. Signs it lists include: vomiting, breakdown of red blood cells (hemolytic anemia, Heinz body anemia), blood in urine, weakness, high heart rate, panting. ASPCA entry.
NC State Extension rates its poison severity for people and animals as low.
If a pet chews a plant and you are worried, call your vet or the ASPCA Animal Poison Control Center (888-426-4435; a fee may apply). For people, call Poison Help at 1-800-222-1222. In an emergency, call 911.
Can you eat onion?
Bulbs and green tops are edible raw or cooked.
Onion questions
When should I plant onions?
Plant sets or transplants 2 to 4 weeks before your average last spring frost. Onions handle cool weather.
Are onions toxic to dogs and cats?
Yes. The ASPCA lists onion as toxic to cats and dogs; it can damage red blood cells.
Why are my onions small?
The variety may not suit your day length, or plants faced weeds or dry soil. Choose a type bred for your region.
Sources
- NC State Extension Gardener Plant Toolbox: Allium cepa (size, light, soil, zones, poison rating)
- USDA PLANTS Database profile: Allium cepa L. (accepted name)
- ASPCA: Onion (pet toxicity)
- ASPCA Animal Poison Control: plants toxic and non-toxic to cats
- ASPCA Animal Poison Control: plants toxic and non-toxic to dogs
- University of Maryland Extension: Starting Vegetable Seeds Indoors
- Colorado State University Extension: Vegetable Planting Guide
Written in our own words from the sources above. See our editorial policy. Spotted a mistake? Tell us.
