When to plant Four-o'clocks in Subtropical Australia

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

Sow four-o'clocks direct from February to September, planting the large seed about 10–15 mm deep once the soil is warm. This frost-tender flower suits the subtropics well, where mild winters let you sow across a long window. Germination takes 14–28 days, and plants flower in roughly 60–90 days, opening their fragrant blooms in the late afternoon. Give each plant plenty of room — space them 50–70 cm apart in rows 30–60 cm apart — as they bush out quickly. In gardens around Brisbane and the Gold Coast they form tuberous roots and often behave as returning perennials.

Sowing calendar — subtropical zone

Green months are your sowing window: February to September.

Growing notes

Four-o'clocks are among the easiest flowers to grow in a subtropical garden — they relish heat and humidity that defeat cool-season plants. The main task is managing their vigour rather than nursing them along.

Give them full sun and space, because they grow into dense, shrubby plants up to a metre across. Crowding them is the usual mistake; packed plants trap humidity, drop their lower leaves and get untidy. The generous 50–70 cm spacing is worth respecting.

They are frost tender, but in the frost-free subtropical winter the tuberous roots survive in the ground and reshoot in spring, so a plant put in near Coffs Harbour or Lismore can return for years. Two things to watch:

• They self-seed heavily. The hard black seeds sprout everywhere, so deadhead if you don't want a colony.
• All parts are toxic if eaten, so site them away from where children or pets graze.

The one real failure mode is poor flowering in shade — in too little sun they grow lush and leafy but skimp on blooms. Plant them in the open, water through dry spells, and they will flower reliably from summer into autumn.

Four-o'clocks at a glance

Common questions

When can I plant four-o'clocks in the subtropics?

Sow direct from February through September while the soil is warm. The mild subtropical winter gives a long sowing window, and plants flower about 60–90 days later. Avoid sowing into cold, wet soil, as this frost-tender plant prefers warmth to germinate.

Do four-o'clocks come back every year in Brisbane?

Often, yes. They form tuberous roots that survive the frost-free subtropical winter in the ground and reshoot in spring, so established plants can return for several years. They also self-seed readily.

Why won't my four-o'clocks flower?

The most common cause is too much shade. Given rich soil and low light they grow leafy but produce few blooms. Move them to a full-sun position and they will flower freely from summer into autumn.

How far apart should four-o'clocks be planted?

Space them 50–70 cm apart, with rows 30–60 cm apart. They grow into large, shrubby plants, and crowding traps humidity and encourages leaf drop in the warm subtropical climate.

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