When to plant Four-o'clocks in Tropical Australia

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

Sow four-o'clocks direct from March to September, dropping the large seed into warm, well-drained soil once the worst of the wet has passed. Plant deep at 10–15 mm, and expect germination in 14–28 days. These bushy, frost-tender flowers hit their stride in the tropics, reaching flowering in 60–90 days and opening their fragrant trumpets in the late afternoon, hence the name. Give them room: space plants 50–70 cm apart with rows 30–60 cm apart, as they make substantial shrubs in a single season. Around Darwin and Townsville the long March-to-September window suits this easy, heat-loving performer perfectly.

Sowing calendar — tropical zone

Green months are your sowing window: March to September.

Growing notes

Four-o'clocks are one of the more forgiving flowers you can grow in the tropics. They love heat, shrug off humidity better than most, and form tuberous roots that let them behave as short-lived perennials, resprouting after the plant is cut back. Sow from March to September into free-draining soil in full sun to light shade, and they will more or less look after themselves.

Germinate the plump seed at 10–15 mm deep; shallow sowing is the usual reason for patchy strikes, since these seeds want the moisture and warmth of proper burial. Once up, give each plant real space, because at 50–70 cm apart they still knit into a solid mass by flowering.

The one caution here is enthusiasm. Four-o'clocks self-seed prolifically and their tubers persist, so in a warm garden around Cairns or Mackay they can naturalise and become weedy. The fix is simple: deadhead before seed drops if you want to keep them contained, and dig out unwanted tubers rather than just cutting the tops.

Water through any dry-season stretch to keep them flowering, mulch to hold moisture, and cut plants back hard after a flush to trigger fresh growth. Slugs and snails may graze young seedlings in the wet, but established plants are rarely troubled.

Four-o'clocks at a glance

Common questions

When do four-o'clock flowers open?

In the late afternoon, usually around four o'clock, which is where the name comes from, and they stay open through the evening releasing a sweet scent. In cooler, overcast weather they may open earlier and last longer into the day.

Do four-o'clocks grow well in Darwin?

Very well. They are heat-loving and humidity-tolerant, thriving through the long March-to-September window and forming tuberous roots that let them resprout year after year. They are one of the easier flowers for tropical gardens.

Are four-o'clocks invasive?

They can be. They self-seed freely and form persistent tubers, so in warm gardens they may naturalise. Deadhead before seed drops and dig out unwanted tubers to keep them contained.

How deep should I sow four-o'clock seeds?

Sow them 10–15 mm deep, which is deeper than most flower seed. Shallow sowing is the usual cause of poor germination, as the large seeds need the moisture of proper burial to strike well in 14–28 days.

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