Subtropical Australia: summer rain, rare frost and what to plant when

Frost and rain

Subtropical Australia covers south east Queensland and northern New South Wales. Summers are warm and humid, with reliable summer rain, winter is mild and much drier, and frost is rare. For a gardener that makes two growing seasons: a warm, wet one that runs from spring through summer and a cool, dry one from autumn to winter, with the brassicas, peas and garlic in the second. The pressure points are heat and humidity in summer, and watering in the dry stretch from late winter to spring.

Frost

BoM’s frost maps show extensive areas of northern Australia as generally frost free, with potential frost days mainly confined to late autumn through early spring. For this zone BoM and CSIRO give the end of the frost risk, from records for 1989 to 2018. At Amberley, west of Brisbane, it typically ended by the end of August but would occasionally continue through September, and at Casino and Kempsey on the north coast it typically ended by mid August. Frost nights have been recorded as late as the third week of September, and the latest at Kempsey was 21 September 1991.

At Amberley the reduction in frosts has been in May, June and July, which shows that frost does reach as early as May. No first-frost date is published, so the start of the season is best taken as May. Dry winters bring a little more frost, about one extra spring frost night at Amberley after a dry winter than after a wet one.

Frost forms on clear, calm nights and cold air settles into the hollows and valley floors, so those are the places to cover tomatoes, basil and young seedlings with fleece or a sheet before dusk.

Rain and watering

Rain is a summer affair. BoM and CSIRO describe summer rain as reliable in south east Queensland and on the north coast, and autumn as unreliable in the south east. The region averaged about 1,030 mm a year in 1989 to 2018, and winter and spring rainfall has decreased. Winter rain is unreliable on the north coast.

That sets the watering calendar. The dry stretch from late winter to spring is when a new planting depends on the hose, so soak deeply a couple of times a week and mulch. In summer the storms do much of the work and the risk turns to fungal disease, so water the soil rather than the leaves and space plants so that the air moves. Indoors, the humid summer keeps compost damp for longer, 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

Warm, humid and wet. Sow beans, beetroot, capsicums, cucumbers, lettuce, pumpkin, sweet corn, tomatoes and zucchini, and pick every day. Water the soil, not the leaves, and watch for mildew. The general list is on January, south of the equator.

February

Late summer. Keep sowing the warm-season crops, and start leeks, onions, carrots and parsnips for the cooler months. Sow lettuce in the shade. The general list is on February, south of the equator.

March

The heat eases, and the second growing season opens. Sow broad beans, broccoli, cauliflower, celery, kale, onions and radish, and carry on with beans and tomatoes. Plant spring bulbs. The general list is on March, south of the equator.

April

The cool, dry season begins. Sow broccoli, cabbage, carrots, garlic, kale, lettuce, onions, peas and spinach, and plant tomatoes while the nights are still mild. Keep the soil moist. The general list is on April, south of the equator.

May

Cooler, and the first frosts are possible in the hollows. Sow beetroot, broad beans, garlic, onions, peas and spinach, and keep the cover handy. The general list is on May, south of the equator.

June

The cool, dry season. Sow beetroot, cabbage, carrots, kohlrabi, lettuce, parsnips and peas, plant garlic, and prepare planting holes for bare-root roses. Water by hand if the weather stays dry. The general list is on June, south of the equator.

July

The coolest month. Sow carrots, celery, kale, lettuce, onions, peas and spring onions, plant asparagus crowns and globe artichokes, and prune roses. In frost-free gardens keep sowing beans, pumpkins and cucumbers. The general list is on July, south of the equator.

August

The frost risk ends during the month, typically by mid to late August. Sow beans, capsicums, cucumbers, potatoes, tomatoes and zucchini, under cover where the hollows are cold. Water new plantings, because this is the dry stretch. The general list is on August, south of the equator.

September

Everything can go in, but frost nights have been recorded as late as the third week of the month. Plant out tomatoes, capsicums, beans and basil, sow sweet corn, pumpkin and sunflowers, and plant dahlias. Mulch and water deeply. The general list is on September, south of the equator.

October

Warm and settled. Plant the summer vegetables and annuals, sow okra and sweet potatoes, and stake the tomatoes. Water deeply twice a week. The general list is on October, south of the equator.

November

Heat and the first storms. Plant the heat-tolerant annuals, and keep sowing beans, zucchini and basil. Protect the young plants with shade cloth. The general list is on November, south of the equator.

December

Hot, humid and stormy. Sow beans, zucchini, basil and coriander, keep the soil mulched, and pick promptly. Space plants so the air moves. The general list is on December, south of the equator.

Plants that belong here

• Tomato is killed by frost, so build the calendar back from the last frost and use the cool half of the year.
• Peppers and chillies need a long warm season, which the subtropics provide.
• Beans are tender and wait for warm soil, so sow them from spring and again in late summer.
• Courgette wants warm soil, full sun and more water than feels sensible, and is picked small and often.
• Cucumber wants warmth, water and something to climb.
• Basil sulks below about 10 °C and runs to flower in a heatwave, so pinch it often.
• Lemon wants bright light and a cool but frost-free winter rest.
• Bougainvillea wants a frost-free winter and flowers best when kept a little stressed.
• Sunflower is an annual built between sowing and the first frost, and needs warm soil and steady water.

Questions from the margin

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