When to plant Spring Onion in Subtropical Australia

Subtropical zone — applies to Brisbane, Gold Coast, Sunshine Coast, Coffs Harbour, Lismore and similar areas. Growing elsewhere? Tropical · Temperate · Cool · Arid.

Spring onions are sown direct in two subtropical windows: March to April in autumn, and July to September from mid-winter into early spring. Germination takes 7–14 days from a 10 mm sowing and the crop turns around in 60–70 days, making them one of the quickest alliums you can grow. Sow short rows and repeat every few weeks within each window rather than committing to one big batch — a staggered supply suits a vegetable you rarely need more than a bunch of at a time.

Sowing calendar — subtropical zone

Green months are your sowing window: March to April and July to September.

Growing notes

The two windows bracket the subtropical winter, and that is no accident: spring onions are hardy through the light frosts inland of Coffs Harbour, but they resent the humid summer, when warm saturated soil rots the shanks and downy mildew furs the leaves. Autumn sowings are the more forgiving, germinating quickly in still-warm soil and then standing in the bed through winter, where they hold their quality for weeks past the 60–70 day mark. Late-winter sowings race away as the days lengthen but need to be pulled before the December humidity arrives.

Free-draining soil matters more than rich soil here — in a heavy Brisbane clay, work in compost and sow along a slight mound so the shanks never sit in water. Draw a 10 mm-deep drill, sow thinly, and thin seedlings to 5–10 cm apart with rows 20–30 cm apart. The classic failure is the unthinned row: crowded seedlings stay pencil-lead thin, stay damp at the base overnight and damp off in the first wet spell. Thin early, water at soil level in the morning, and start pulling the thickest plants first so the remainder keep sizing up. Any plants still in the ground when summer humidity builds should come out and go in the fridge rather than be left to rot.

Spring Onion at a glance

Companion planting

Grows well with

Carrot: Scent deters carrot fly

Keep away from

Bean (Bush): Alliums inhibit legume growth

Common questions

When do I plant spring onions in the subtropical zone?

Sow direct in March and April, or from July to September. Both windows aim the crop at the mild months and keep it clear of the humid summer.

Why are my spring onions so thin?

Overcrowding is the usual cause — unthinned rows produce spindly stems. Thin seedlings to 5 to 10 cm apart early, and harvest the largest plants first so the rest can thicken.

How long do spring onions take from seed?

About 60 to 70 days from sowing to harvest, with germination in 7 to 14 days. Sowing a short row every few weeks gives a continuous supply through the season.

Can I grow spring onions over summer in Brisbane?

It is best avoided. Warm, saturated summer soil rots the shanks and encourages downy mildew, which is why the sowing windows close before the wet season.

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