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🔍 Click to enlargevegetablebiennial
Onion
Allium cepa
Kitchen staple that stores for months. Choose short- or long-day varieties for your latitude.
Quick Facts
Sun:☀️ Full Sun
Water:💧💧 Moderate
USDA Zones:Zones 3–11
Space:🪴 Container, 🌱 Small Bed, 🏡 Large Garden
Soil:Loam, Sandy, Silty
Best Season(s):Spring
Experience Level:🌱 Beginner
Native Range:Central Asia
Bloom Color:White, spherical flower cluster if allowed to bolt (grown for bulb)
Bloom Cycle:Blooms in its second year if left in the ground
Days to Harvest:90–120 days
Harvest Pattern:Single harvest per planting
Care Notes
Match day-length variety to your region. Stop watering when tops begin to fall over.
Growing Details
Mature Size:12-18 in tall, 4-6 in wide (bulb 2-4 in diameter)
Growth Rate:🐢 Slow
Zone Performance
Day-length variety matching matters more than zone alone: short-day varieties bulb properly in zones 8-11's shorter winter daylight, while long-day varieties are required for reliable bulbing in zones 3-6 where summer days are longer; intermediate-day types bridge zones 6-7. Getting this wrong is the most common reason gardeners report onions that never bulb up.
Companions & Wildlife
🦌 Deer Resistance
rarely damaged
The sulfur-compound scent and taste of the foliage and bulb make onion one of the most reliably deer-proof vegetable crops.
🐝 Pollinator Value
low
Bulbing onions are harvested before flowering, but plants left to bolt produce large globe-shaped umbels that honeybees and native bees readily visit.
Good Companions
Tomato — Alliums' strong scent helps confuse and deter many common tomato pests.
Carrot — Onion scent genuinely reduces carrot fly pressure through scent confusion — one of the better-supported companion planting effects.
Beet — Compatible growth habits and non-competing root structures.
Troubleshooting
⚠️ Bulbs stay small or fail to form
Confirm you're growing a day-length type matched to your latitude, and keep beds weed-free since onions compete poorly with weeds for nutrients.
⚠️ Thrips causing silvery streaks on leaves
Spray with insecticidal soap and keep nearby weeds mowed, since thrips overwinter in grassy vegetation adjacent to onion beds.
⚠️ Bulbs rot in storage
Stop watering once tops flop over, cure bulbs in a warm dry spot for 2-3 weeks before storage, and only store fully dry, thick-necked bulbs.
⚠️ Pet Safety
Toxic to cats and dogs (thiosulfates) — can damage red blood cells; every part of the plant should be kept away from pets.
Informational only — always check with a veterinarian if you suspect your pet has eaten something it shouldn't have.