Spring Onion (scallion) care

Light

Spring Onion needs sun on the leaves, not just bright ambient room light. Full sun for fast, sturdy growth and crisp shanks; tolerates light shade with slightly slower, leggier results. Even a sunny windowsill or container works for these compact plants. A south or west-facing windowsill in the northern hemisphere is the default; anywhere else, expect the plant to stretch and pale out within a season.

Watering

Outdoor spring onion crops want when the top 2 cm of soil is dry, about every 3-5 days; keep evenly moist. The single best habit is a finger-test before watering — push a finger 3-4 cm into the soil. Damp = wait a day; dust-dry = water deeply at the base of the plant. Shallow-rooted and quick-growing, so they need regular light watering to stay tender and mild. Dry spells make the leaves tough and the flavour sharper and can stall growth.

Soil and pot

Spring Onion grows best in light, fertile, free-draining soil, ph 6.5-7.5. Wants a finely raked, weed-free seedbed with moderate fertility. Heavy compacted or waterlogged soil rots the slender shanks; add compost for moisture retention in light sandy ground. A pot with a working drainage hole is non-negotiable for this species — even free-draining mix will turn soggy in a closed planter. If you love the look of a decorative pot without a hole, use it as a cachepot around an inner nursery pot you can lift out to water.

Humidity and temperature

Spring Onion sits happiest at around Ambient outdoor humidity and 10-24°C (50-75°F). No special humidity requirement; an easy outdoor or container crop. Avoid overhead watering late in the day to limit downy mildew on the leaves. If you keep the room above 10 year-round and avoid placing the plant near a cold draught, a hot radiator, or an air-conditioning vent, you have already handled the two biggest indoor stressors.

Fertilising

Feed spring onion sparingly. Light feeder grown fast in fertile soil; usually no extra feed is needed for a short crop. For successional rows or overwintered plants, a light balanced or seaweed feed once or twice keeps the leaves lush and green. Skip fertiliser entirely on a stressed, recently-repotted, or actively wilting plant — fertiliser salts make damage worse, not better. Wait for a round of healthy new growth before resuming a feeding rhythm.

Common problems

Below are the issues we see most often on spring onion in the Growli community. Each is annotated with the most common cause so you know where to start.

• Downy mildew — Pale patches with greyish mould on the leaves in cool wet weather. Improve spacing and airflow, water at the base, and rotate alliums around the plot.
• Onion fly — White maggots burrow into the base, causing wilting and collapse of young plants. Use insect-proof mesh and avoid leaving thinnings lying around, which attract the flies.
• Slow germination in cold soil — Seed sown into cold wet ground rots or germinates patchily. Wait for soil to warm, or sow in modules and transplant in clumps.
• Bolting — Overwintered or stressed plants run to flower in spring, toughening the shank. Sow appropriate winter-hardy strains for overwintering and harvest before flowering.

Propagation

Grown from seed. Sow thinly direct 1 cm deep from early spring, repeating every 2-3 weeks for a continuous supply; a hardy 'White Lisbon Winter Hardy' sowing in late summer/early autumn overwinters for an early crop. Can also be multi-sown in modules and planted as small clumps. Propagation is the cheapest, most satisfying way to expand a collection — and it doubles as insurance against losing a mature plant to an accident. Take a backup cutting once the parent is established and healthy.

Toxicity to pets

Spring Onion is toxic to pets. ASPCA lists Allium species, which includes spring onions/scallions, onions, garlic, leeks and chives, as toxic to dogs and cats. The organosulfoxides they contain cause oxidative red-blood-cell damage and Heinz-body haemolytic anaemia, with cats most sensitive. Watch for vomiting, lethargy, pale gums, weakness and dark urine; the toxin survives cooking. If you keep cats, dogs, or curious children in the house, weigh placement carefully — a high shelf or a hanging planter is enough for casual safety. For severe ingestion incidents, call your local vet and the ASPCA Animal Poison Control Center (in the US, 888-426-4435).

Pet-safety status is sourced from the ASPCA Toxic and Non-Toxic Plant List, which catalogues the most-asked-about plants for cats, dogs, and horses.

Spring Onion deep-dive guides

Every aspect of spring onion care, each with its own calibrated guide:

• Spring Onion watering schedule
• Spring Onion light requirements
• Best soil mix for spring onion
• Spring Onion fertilizing guide
• When to repot spring onion
• How to propagate spring onion
• Spring Onion growth rate & size
• Spring Onion cold hardiness
• Spring Onion temperature & humidity
• Is spring onion toxic to cats & dogs?
• Is spring onion toxic to cats?
• Is spring onion toxic to dogs?

Related guides

Spring Onion is also known as White Lisbon spring onion, scallion, and green onion.

• Tomato care — light, water and common problems
• Pepper care — light, water and common problems
• Cucumber care — light, water and common problems
• All 2464 plant care guides in the Growli library