When to plant Nasturtiums in Tropical Australia

Tropical zone — applies to Darwin, Cairns, Townsville, Broome, Mackay and similar areas. Growing elsewhere? Temperate · Cool · Subtropical · Arid.

Sow nasturtiums direct from February to September, dropping the large seeds 10–15 mm deep straight where they are to grow. Across Darwin, Cairns and Townsville this window covers the tail of the wet and the whole dry season, when soil is workable and seedlings are not battered by monsoon downpours. Germination takes 14–21 days once the seed coat softens, and plants reach useful size in 70–80 days. Space them 20–40 cm apart in rows about 30 cm apart. They sprawl and self-seed readily, so give them room to trail over a bed edge or scramble up a low support.

Sowing calendar — tropical zone

Green months are your sowing window: February to September.

Growing notes

Nasturtiums are one of the easiest flowers to grow in the tropical dry season, tolerating poor soil and shrugging off neglect. In fact, they flower best when you resist feeding them: rich, nitrogen-heavy beds push lush leaves and almost no blooms. Plant into ordinary or even lean soil, water when the top few centimetres dry, and let them do the rest.

The main failure mode here is the wet season. Sustained humidity and warm nights invite fungal leaf spots and rot, and heavy rain flattens the soft foliage. That is why the sowing window closes in September, ahead of the November build-up. If you want colour into the early wet, grow them in a pot under eaves where you can control moisture.

Aphids will find them, and that is partly the point. Nasturtiums make an excellent trap crop, pulling aphids and cabbage white butterflies away from nearby tomatoes, broccoli, cabbage, cauliflower, kale and Brussels sprouts. Plant a border around your brassicas and inspect the nasturtium leaves rather than the crop. A firm hose blast knocks aphid colonies down without spray. The leaves and flowers are edible, with a peppery bite worth adding to salads.

Nasturtiums at a glance

Companion planting

Grows well with

Tomatoes: Trap crop for aphids; lures them away from tomatoes

Broccoli: Trap crop for cabbage white butterfly caterpillars

Cabbage: Trap crop lures cabbage white away from brassica

Common questions

When should I plant nasturtiums in Darwin?

Sow direct any time from February to September, which spans the end of the wet and the full dry season. Avoid the November to April monsoon, when humidity and downpours rot the soft foliage. A dry-season sowing gives the longest, healthiest flowering run.

Why are my nasturtiums all leaves and no flowers?

This almost always means the soil is too rich in nitrogen. Nasturtiums flower best in lean ground, so stop feeding and let them run a little hungry. Blooms usually follow within a few weeks once the leafy growth slows.

Do nasturtiums really protect other vegetables?

Yes, they work as a trap crop for aphids and cabbage white butterflies, luring pests away from tomatoes and brassicas like broccoli, cabbage, cauliflower and kale. Plant them as a border and check the nasturtium leaves for pests instead of your main crop.

Can you eat nasturtium flowers?

The flowers and young leaves are both edible and have a peppery, watercress-like flavour. Scatter them through salads or use the blooms as a garnish. The green seed pods can also be pickled like capers.

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