Onion (Allium cepa) care guide

Allium cepa is commonly called onion. It is a bulb-forming vegetable in the genus Allium and family Amaryllidaceae.

Onions need full sun, ideally at least 6 hours of direct sunlight daily. Strong light supports healthy leaves and larger bulbs.

Grow onions in fertile, loose, well-drained loam or sandy loam amended with organic matter. Avoid compacted or waterlogged soil because shallow onion roots are vulnerable to poor drainage.

Onion seedlings and transplants tolerate light frost. Prolonged freezing, repeated temperature swings, or planting oversized sets before winter can increase stress and the risk of bolting.

You can grow green onions indoors in a bright, sunny location, but producing full-size bulbs indoors is difficult without strong light, adequate space, and a suitable growing period. A sunny outdoor bed usually gives better bulb results.

Water onions to keep the soil evenly and consistently moist, especially while bulbs are enlarging. Avoid severe drying followed by heavy watering, which can stress plants and contribute to splitting.

Small bulbs usually result from an unsuitable day-length type, late planting, inadequate sunlight, drought, crowding, or poor nutrition. Onions need enough leaf growth before day length triggers bulbing, so early planting and steady moisture are important.

Falling, yellowing, and drying tops usually indicate that mature bulb onions are nearing harvest. Harvest when roughly half the tops have naturally fallen, particularly before prolonged wet weather arrives.

Harvest mature onions when the tops wither, fall over, and begin turning brown. Green onions and scallions can be harvested earlier whenever the leaves and stems are large enough to use.

Cure onions in a warm, dry, well-ventilated place for about 2–4 weeks, until the outer skins are papery and the necks are tight. If outdoor conditions are wet, cure them indoors instead.

Store properly cured onions in a cool, dry, dark, well-ventilated location and protect them from freezing. Discard bulbs that are bruised, cut, soft, diseased, or beginning to rot.

Storage life depends on variety and curing quality; pungent yellow storage onions generally keep longer than sweet onions. Inspect them regularly and use any bulbs that begin to soften or sprout.

Onions benefit from fertile soil and balanced nutrition, especially adequate nitrogen during leaf growth. Avoid excessive nitrogen late in the season because it can delay maturity and reduce storage quality.

Common onion pests include onion maggots, thrips, and various caterpillars. Yellowing and wilting can indicate root or stem injury, so use clean planting material, rotate crops, remove affected plants, and follow local integrated pest-management guidance.

Yellowing and wilting may result from drought, waterlogged soil, disease, or onion maggot injury. Check soil moisture, inspect roots and the bulb base, and remove severely affected plants rather than keeping them in the bed.

Avoid repeatedly cutting the green leaves of bulbing onions because the leaves provide energy for bulb development. Harvest individual leaves only sparingly, or grow separate plants specifically for green onions.

Plant onions in early spring as soon as the soil is workable, adjusting the timing to your USDA growing zone and variety. In suitable climates, some types can also be planted in late summer or fall for overwintering.

Onion sets are usually the easiest option for beginners, while transplants often provide more reliable variety selection and bulb development. Choose firm, healthy, dormant sets or plants without soft spots or decay.

Sow onion seeds about ¼ to ½ inch deep. Keep the seedbed evenly moist until emergence, then thin seedlings so developing bulbs have adequate room.

Space bulbing onions about 3–6 inches apart, depending on the desired bulb size and variety. Green onions can be planted closer, commonly about 2–3 inches apart, and harvested while young.

Choose varieties by day length: long-day onions suit much of the northern United States, short-day onions perform better in southern regions, and intermediate or day-neutral types fit many areas between them. Local extension recommendations and seed descriptions are useful guides.

Yes, onions grow well in containers that have drainage holes, fertile potting mix, full sun, and consistent moisture. Use a container wide enough for the spacing required by the selected bulb or green-onion variety.

Yes, onions can be grown from seed, transplants, or sets. Starting seed indoors about 10–12 weeks before outdoor planting gives gardeners the widest choice of varieties and strong plants at transplanting time.

A leftover onion base may regrow leaves and roots, but it usually will not produce a full replacement bulb. For dependable harvests, grow onions from seed, transplants, or commercially produced sets.

Yes, a bolted onion is generally edible if it is firm and free of rot. Its bulb may be smaller or have a tougher center, so use it fresh rather than relying on long-term storage.

Yes, onions are toxic to dogs and cats and can damage red blood cells, potentially causing anemia. Keep bulbs, scraps, cooked onions, dried onion, and onion powder away from pets and contact a veterinarian promptly after ingestion.

Yes, onion bulbs and green parts are generally edible for humans when fresh and properly prepared. Do not eat bulbs that are moldy, rotten, or contaminated, and do not confuse onion toxicity to pets with human edibility.

Onions bolt when they produce a flower stalk, often after cold exposure, temperature fluctuations, stress, or planting oversized sets. Remove the stalk if desired and harvest the bulb soon, because bolting onions generally store poorly.

Yes, onions are biennial plants that can produce a tall flower stalk and a rounded flower head when they bolt. The flowers may produce seed, but bolting usually reduces the quality and storage life of the bulb.