When to plant Nasturtiums in Cool Australia

Cool zone — applies to Hobart, Canberra, Ballarat, Orange, Armidale and similar areas. Growing elsewhere? Temperate · Subtropical · Tropical · Arid.

Sow nasturtiums direct from September to December, once the last hard frosts have cleared the beds around Hobart, Canberra and Orange. These are frost-tender annuals, so wait until the soil has warmed rather than risking an early sowing. Push the large seeds in 10–15 mm deep, spacing plants 20–40 cm apart with rows about 30 cm apart. Germination takes 14–21 days, and you can expect flowers and peppery leaves from around 70–80 days. They thrive on neglect and poor soil, making them one of the easiest starts for a cool-climate cottage bed.

Sowing calendar — cool zone

Green months are your sowing window: September to December.

Growing notes

Nasturtiums are almost too easy in cool districts, provided you get the timing right. The single most common failure here is sowing too early: a frost tender seedling caught by a late-season cold snap in Ballarat or Armidale will simply blacken and collapse. Hold off until nights are reliably above freezing, usually from mid to late spring.

The second trap is too much kindness. Rich, heavily fertilised soil pushes lush foliage and almost no flowers, so plant them in your poorest, sunniest bed and go easy on the watering can once established. A dry, lean position gives you far more of those bright blooms.

Nasturtiums earn their keep as a trap crop. Aphids and cabbage white butterfly are drawn to them ahead of your brassicas, so a border sown near broccoli, cabbage, kale, cauliflower or Brussels sprouts pulls pest pressure away from the crop you actually want. Check the nasturtium leaves for aphid clusters and squash or hose them off before the colony explodes. In short cool summers, give the plants full sun to maximise flowering before the first autumn frosts return.

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 to plant nasturtiums in Canberra

Wait until the last frosts have passed, generally from September through December in Canberra's cool climate. Sowing into cold, frost-prone soil risks losing the frost-tender seedlings, so later spring is safer than an early gamble.

why are my nasturtiums all leaves and no flowers

This is almost always too much nitrogen. Rich or freshly fertilised soil pushes leafy growth at the expense of blooms, so grow nasturtiums in poor soil and full sun and ease off the watering once they are established.

do nasturtiums protect brassicas from cabbage moth

They work as a trap crop, luring aphids and cabbage white butterfly to themselves and away from broccoli, cabbage, kale and cauliflower. Plant a border of them nearby and check the nasturtium leaves regularly for the pests they attract.

how deep do you sow nasturtium seeds

Sow the large seeds 10–15 mm deep directly where they are to grow, spacing plants 20–40 cm apart. They resent transplanting, so direct sowing gives the best results.

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