How to grow Onion in New Zealand
Onions are a long, easy crop: sow or plant once and harvest five or six months later, then store the bulbs for months. Pukekohe Long Keeper, bred for New Zealand conditions, is the most widely grown variety here and keeps for up to ten months. Timing matters, because onions bulb in response to day length, and sowing at the wrong time makes them bolt or stay small.
📖 Our full guide: How to Grow Onion in New Zealand
At a glance
When to sow by region
| Region | When to sow | Regional note |
|---|---|---|
| Northland | March to September | |
| Auckland | March to September | |
| Waikato & Bay of Plenty | March to September | |
| Central North Island | March to September | |
| Wellington & Lower North Island | March to September | |
| Nelson & Marlborough | March to September | |
| Canterbury | March to May, August and September | Sow in autumn to overwinter, or in Aug to Sep for a summer bulb. Midwinter sowings sit and rot. |
| Otago & Southland | April and May, August and September | Sow Apr to May to overwinter, or Aug to Sep for a summer bulb. |
| Central Otago | August to October | Sow in spring. Autumn sown onions often bolt or die after a hard winter here. |
Where to plant
Grow onions in full sun in well-cultivated, free-draining soil enriched with compost and sheep pellets before planting. Let the ground settle for a week or so before sowing; onions like a firm bed. Keep the area weed free, as onions compete poorly.
Rotate onions with other crops and keep them out of beds where garlic, leeks or onions had white rot, a soil-borne disease that persists for many years.
- Northland, Auckland, Waikato and Bay of Plenty, the central North Island, Wellington, and Nelson and Marlborough: sow from March to June for harvest in late spring and summer. Pukekohe Long Keeper can also be sown from July to September, according to Kings Seeds.
- Canterbury: sow in autumn, March to May, to overwinter, or in August and September for a summer bulb. Midwinter sowings sit and rot.
- Otago and Southland: sow in April and May to overwinter, or in August and September for a summer bulb.
- Central Otago: sow in spring, August to October. Autumn-sown onions often bolt or die after a hard winter here.
Choosing a variety
| Variety | Notes |
|---|---|
| Pukekohe Long Keeper | The New Zealand market standard: high-yielding, medium brown bulbs with pungent flavour that store up to ten months; good bolting tolerance |
| Red Brunswick | Bright red onions with a milder flavour |
| Yellow Sweet Spanish | Large, mild, sweet golden onions up to 500 g; best used fresh rather than stored long |
| Californian Red | Large, round, plum-red onions; best used within a few months |
| Pearl Drop and Purplette | Small white and red mini onions that mature quickly, for salads and pickling |
Onions are day-length sensitive, so choose varieties sold for New Zealand conditions and sow at the time on the packet.
How to plant
- Sow seed thinly about 6 mm deep in a shallow drill, or in trays. Sowing too deep gives thick necks that store poorly. Seed germinates in about 7 to 14 days.
- If sown in trays, transplant seedlings when they are about 10 cm tall and can be handled; they look like grass and are delicate.
- Thin or plant seedlings about 10 to 15 cm apart in rows about 20 cm apart. Plant seedlings shallowly, with the base just below the surface.
- Water in and keep the bed weeded, especially while seedlings are small.
- Garden centres also sell onion seedlings in punnets through the planting season.
Watering and feeding
Keep the soil moist but not wet. Onions need plenty of water as the bulbs form, which in New Zealand is mostly November and December. Ease off once the tops start to fall over, so the bulbs ripen and store well.
Feed every four weeks or so during active growth with a vegetable fertiliser. Pea straw mulch helps keep weeds down and moisture in.
Harvesting
Onions are ready in late spring to summer, five to six months after sowing, when the tops yellow and fall over. Do not pull them by the leaves, which can snap; lift them gently with a fork.
Leave the bulbs to dry on top of the ground, or under cover if rain is forecast, for about a week, until the skins are papery and the necks dry. Then plait or bag them and store somewhere dry, airy and out of direct sun. Long keepers last up to six months or more in good conditions.
Growing in pots
Onions grow in pots and troughs with at least 20 cm of rich, moist vegetable mix, though yields are small. Mini onions and spring onions suit containers best.
Companion planting
Onions take little space and grow well alongside many vegetables. Keep them away from beans and peas, as traditional advice suggests.
Good companions
- Carrot A traditional pairing; the onion scent may help mask carrots from carrot rust fly.
- Beetroot A root crop that shares the bed comfortably.
- Lettuce Quick lettuce can grow between onion rows early in the season.
- Silverbeet A traditional companion that shares the bed easily.
- Chamomile A traditional companion said to help onions.
Keep apart
Avoid planting these close to onion.
Pests and diseases
Thrips and downy mildew are the most common onion problems in New Zealand gardens. White rot is less common but very serious.
Pests to watch for
- Thrips Silvery, mottled streaks on the leaves in hot, dry weather.
Diseases to watch for
- Downy mildew Pale, oval patches on the leaves with a grey-violet fuzz in cool, damp weather; leaves collapse.
- White rot Yellowing, dying plants with white mould and tiny black specks on the base of the bulb. Remove with the surrounding soil and do not grow onions there again.
- Onion smut Dark streaks and blisters on seedling leaves that burst to release black spores; seedlings die. Rotate and use clean seedlings.
Common questions
When do I plant onions in New Zealand?
In most of the North Island and the top of the South, sow from March to June; Pukekohe Long Keeper can also go in from July to September. In Canterbury, Otago and Southland sow in autumn to overwinter, or in August and September for a summer crop. In Central Otago sow in spring.
Why have my onions gone to seed?
Onions bolt when sown at the wrong time for the variety or when growth is checked by cold or dry spells. Sow at the time on the packet and choose varieties bred for New Zealand, such as Pukekohe Long Keeper, which has good bolting tolerance.
When are onions ready to harvest?
When the tops yellow and fall over, usually five to six months after sowing. Lift them with a fork rather than pulling.
How do I store onions?
Dry the bulbs in the sun or under cover for about a week until the skins are papery and the necks dry, then plait or bag them and keep them dry, airy and out of direct sun.
Why are my onions small?
Usually late sowing, crowding, weeds or dry soil while the bulbs were forming in November and December. Thin to 10 to 15 cm, weed well and keep them watered as the bulbs swell.
Can I grow onions in a pot?
Yes, in a pot or trough with at least 20 cm of rich mix, although yields are small. Mini onions and spring onions are the best choices for containers.
Sources we checked: Tui: Onion growing guide; Yates NZ: How to grow onions; Kings Seeds NZ: Onion Pukekohe Long Keeper; Kings Seeds NZ: Onion Yellow Sweet Spanish.