Tropical Australia: a wet season, a dry season and no frost

Frost and rain

Tropical Australia is the top end of the continent, from Exmouth in the west to south of Townsville in the east. There are two seasons rather than four, a wet season and a dry season, and there is no frost. Darwin Airport averaged 327 days a year above 30 °C in 1989 to 2018. For a gardener it reverses the temperate habits: the main vegetable season is the dry, and the wet season, which is hot, humid and drenching, is the time for tough tropical plants and for keeping beds drained and mulched.

Frost

There is no frost to plan for. BoM’s frost maps show extensive areas of northern Australia as generally frost free, with frost potential elsewhere increasing with elevation. No first or last frost date is published for the tropics, so this page gives none, and the planting windows follow the rain and the heat instead. Heat and rain, not cold, set the limits on what grows.

The cold that matters is indoors. The croton and caladium entries give minimum temperatures of 15 and 18 °C, which a tropical garden meets all year but a cooled room may not.

Rain and watering

BoM and CSIRO put the wet season at November to April, with a build-up from October to December and the monsoon from January to April. In Darwin the wet season rainfall was 1,732 mm over the last 30 years, up from 1,586 mm, and in the Wet Tropics the whole year brings about 1,980 mm. Further west, in the northern Rangelands of Western Australia, the annual total is about 510 mm.

Around Darwin the wet season typically begins in the last week of October, and in Katherine and the Victoria River district a few weeks later, in mid November. Early rain is not always reliable, and over the last 30 years about 30 percent of seasons in the western Top End had a false start. In the dry season, water daily in the early morning and mulch heavily. In the wet season the problem is too much: choose a sunny, sheltered, well drained site and raise the beds by 10 to 15 cm. Indoors, the humidity keeps compost damp for longer in the wet, so check before watering.

Month by month

Each month below adds the local timing to the matching southern hemisphere page, which has the general list.

January

Monsoon, hot, humid and wet. Plant crops that cope with it, such as Malabar greens, luffa, choko, eggplant, chilli and sweet corn, in raised beds. Do not sow fine seed directly into the open ground, where the rain washes it away. The general list is on January, south of the equator.

February

The monsoon is at its height. Keep beds mulched and raised, pick regularly, and watch for rot in crowded plants. This is a good month to prepare the dry-season beds. The general list is on February, south of the equator.

March

The rain eases towards the end of the month. Sow cucumbers, capsicums, tomatoes, eggplant and beans in trays, and start the beds for the dry season. Dig in compost. The general list is on March, south of the equator.

April

The wet season ends and the main vegetable season begins. Sow tomatoes, capsicums, beans, cucumbers, lettuce, pumpkin and sweet corn, and sow herbs such as coriander and dill. Mulch straight after planting. The general list is on April, south of the equator.

May

The dry season is well under way. Sow beans, tomatoes, capsicums, cucumbers, carrots, lettuce, pumpkin and rocket. Water deeply early in the morning. The general list is on May, south of the equator.

June

Dry, and the middle of the main vegetable season. Sow tomatoes, beans, capsicums, cucumbers, carrots and lettuce, along with coriander, dill and parsley. Keep the beds mulched. The general list is on June, south of the equator.

July

Still dry. Keep sowing the main crops, and plant out seedlings raised in trays. Water every morning, because the soil dries quickly. The general list is on July, south of the equator.

August

The heat is building. Sow the last of the cool-season crops and start the heat-lovers: okra, cucumber, pumpkin and watermelon. Mulch thickly. The general list is on August, south of the equator.

September

Hot and dry, with the build-up approaching. Sow okra, sweet potato, peanuts and sweet corn, and shade the seedlings. Water daily. The general list is on September, south of the equator.

October

The build-up, with the heat and humidity at their worst. Plant taro, turmeric and sweet potato, and make sure the beds drain. Around Darwin the wet season typically begins in the last week of the month, but a first storm can be a false start. The general list is on October, south of the equator.

November

The wet season begins, from the last week of October at Darwin to mid November at Katherine. Plant taro, turmeric and ginger, and hold off on fine seed. Raise the beds and mulch. The general list is on November, south of the equator.

December

The wet season is under way. Plant choko, luffa, okra, rosella, ginger and Malabar greens. Direct seeding between December and February is hard because heavy rain washes the seed away. The general list is on December, south of the equator.

Plants that belong here

• Taro wants warmth, rich soil and a root run that is never dry, and tolerates wet soil.
• Croton comes from tropical islands and coasts with no cool season, and wants bright light and warm, humid air.
• Caladium performs through the warm months and wants shade from direct sun, warmth and steady moisture.
• Bougainvillea flowers under stress, with a proper drying out between soakings, which suits the dry season.
• Crown of thorns flowers almost continuously in full sun, but is spiny and has caustic sap, so place it carefully.
• Basil is a warm weather annual from tropical Asia, and runs to flower in a heatwave, so pinch it often.
• Peppers and chillies need a long warm season, which the tropics provide.
• Cucumber wants warmth, water and something to climb.
• Green beans are tender and need warm soil, and do best in the dry season.

Questions from the margin

Read on

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