Fertilising guide
How to fertilise Spring Onion (Allium fistulosum 'White Lisbon')— schedule & NPK
Also called White Lisbon spring onion, scallion, green onion.
More about spring onion
About Spring Onion
Allium fistulosum 'White Lisbon' · also called White Lisbon spring onion, scallion · edible
Spring onions are quick, non-bulbing alliums grown for their slim white shanks and hollow green tops, eaten whole and raw. 'White Lisbon' is the classic fast, hardy variety, ready in roughly eight weeks from sowing and good for succession crops or overwintering for an early spring pick. They need little space and crop heavily from a short row.
Growth habit: Clumping, non-bulbing allium forming clusters of slender upright white shanks topped with hollow tubular green leaves; harvested young before any bulb forms.
Watch for — 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.
What fertiliser spring onion actually wants — and why
Spring Onion stores its crop underground, so the rule is the reverse of leafy plants — go easy on nitrogen, which sends energy into tops at the expense of roots.
Low-nitrogen, with modest phosphorus and potassium for root development — ideally compost-improved soil rather than a high-N feed. Excess nitrogen forks the roots and grows lush tops instead of a crop.
For the language behind the three numbers on the bottle — what nitrogen, phosphorus and potassium each do — see the NPK ratio explained entry. The short version for spring onion: match the feed to the job the plant is doing right now, not to a generic “plant food” on the shelf.
How often to feed spring onion, and which months
Feeding only earns its keep while the plant is in active growth and can use the nutrients — pour feed into a dormant or low-light plant and it simply builds up as root-burning salt. For spring onion:
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. In practice: prepare the bed with well-rotted compost (not fresh manure), then little or no extra feeding through the season (spring through early autumn); a light potassium feed mid-growth at most.
The dormant-season rule matters more than the exact interval: skip feeding entirely when spring onion is resting. For the wider context on indoor feeding rhythms across the seasons, the houseplant fertiliser schedule walks through the year month by month.
What strength to mix for spring onion
Less is more for spring onion. If you feed at all, keep it light and low-nitrogen — the soil preparation does the work, and over-feeding actively spoils the crop.
Feeding always goes onto already-damp soil, never dry roots — water spring onion first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the spring onion watering schedule.
Signs you are over-feeding spring onion
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for spring onion:
- Large lush leafy tops and small, forked or hairy roots.
- Split or cracked roots from a nitrogen-and-water surge.
- All foliage and no usable crop at harvest.
Signs you are under-feeding spring onion
- Genuinely uncommon in reasonable soil — these are not hungry plants.
- Pale, weak tops and small roots only in very poor, exhausted ground.
- Slow growth across the whole bed in long-uncultivated soil.
If the symptoms point at watering, light or roots rather than nutrition, the full spring onion care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Flushing is not the issue for spring onion — the equivalent care is avoiding fresh manure and high-N feeds entirely, and rotating beds so the soil is not over-rich from a previous hungry crop.
Organic vs synthetic feeds for spring onion
Organic options
Well-rotted compost worked in the season before, or for a previous crop, is ideal — never fresh manure. UK: garden compost, low-N blends; US: Espoma Garden-tone sparingly or finished compost. Lean and well-worked beats rich.
Synthetic / liquid feeds
If anything, a low-nitrogen, potassium-leaning feed only — UK: a high-potash feed mid-season at most, never a general high-N; US: a 5-10-10 sparingly. Most root crops crop best with no synthetic feed at all.
Brand names are examples, not endorsements, and UK and US ranges differ — check the label’s own NPK and dilution rate, since formulations change.
Fertilising spring onion — frequently asked questions
What fertiliser does spring onion need?
Low-nitrogen, with modest phosphorus and potassium for root development — ideally compost-improved soil rather than a high-N feed. Excess nitrogen forks the roots and grows lush tops instead of a crop. Spring Onion stores its crop underground, so the rule is the reverse of leafy plants — go easy on nitrogen, which sends energy into tops at the expense of roots.
How often should I feed spring onion?
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. 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. In practice: prepare the bed with well-rotted compost (not fresh manure), then little or no extra feeding through the season (spring through early autumn); a light potassium feed mid-growth at most.
What strength of feed for spring onion?
Less is more for spring onion. If you feed at all, keep it light and low-nitrogen — the soil preparation does the work, and over-feeding actively spoils the crop.
What does over-feeding spring onion look like?
Large lush leafy tops and small, forked or hairy roots. Split or cracked roots from a nitrogen-and-water surge. All foliage and no usable crop at harvest. Feeding spring onion a nitrogen-rich fertiliser, or planting into freshly manured ground, is the defining mistake — you get a forest of leafy tops and forked, hairy, split or all-leaf-no-root crops.
Should I flush the soil of spring onion?
Flushing is not the issue for spring onion — the equivalent care is avoiding fresh manure and high-N feeds entirely, and rotating beds so the soil is not over-rich from a previous hungry crop.
Keep reading
- Spring Onion care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water spring onion — the watering schedule
- The houseplant fertiliser schedule — feeding through the year
- NPK ratio explained — what the three numbers on the bottle mean
- How to fertilise tomato
- How to fertilise pepper
- How to fertilise cucumber
- All 2464 fertilising guides in the Growli library