How to grow Watermelon in Australia

Where to plant

Watermelons need the sunniest spot you have, at least six hours of direct sun, and plenty of room: each vine spreads about 1.5 m by 1.5 m or more. The soil should be free draining and rich in compost. On heavy clay, build mounds. Raised mounds of compost and manure also warm up faster and drain better in wet weather.

Seed needs soil above about 20°C to germinate, and the vines need a long, hot season of 100 or more warm days. Small-fruited varieties ripen sooner, which helps in cooler or shorter seasons.

• South East Queensland and the Northern Rivers: sow from September to February.
• Sydney: sow from September to January, or start seedlings indoors in late August.
• Adelaide: sow under cover in September, or directly from October to November into warm soil. Long, hot summers ripen melons well with deep weekly watering.
• Perth: sow from August to November once the soil passes about 20°C. Later sowings run out of season.
• Melbourne: sow from October to December, as early as the soil allows. The short summer risks immature fruit before the May frosts, so choose small, quick varieties.
• Canberra: sow in November after the last frost, with quick, small-fruited varieties only. Hobart: not suited outdoors.
• North Queensland and Darwin: a dry season crop. Sow from April to August, like the commercial winter crops around Bowen and in the Top End. Wet season fruit splits and rots.

Choosing a variety

• Small or icebox types, around 2 to 4 kg, ripen in about 10 to 14 weeks, suit small gardens and can be grown on a trellis. They are the best choice for Melbourne, Canberra and other short-season areas.
• Large, long-season types can reach 10 kg or more but need 16 to 20 weeks of heat, so they suit Queensland, the inland and the tropics.
• Seedless watermelons are sterile hybrids and need a seeded variety planted nearby as a pollinator.

How to plant

1. Wait until the soil is warm, above about 20°C, and frost has passed. In cooler areas, start seeds indoors in pots a few weeks earlier and plant them out without disturbing the roots.
2. Build low mounds of soil mixed with compost and well-rotted manure, about 1 to 1.5 m apart.
3. Sow three or four seeds about 2 cm deep in each mound.
4. Water in and keep the soil just moist. Seedlings appear in about a week.
5. Thin to the strongest one or two seedlings per mound, and mulch around them with straw once they are growing.

Watering and feeding

Consistent moisture is the key. Water deeply at the base of the plants whenever the top few centimetres of soil are dry, rather than little and often, and keep the leaves dry to limit mildew. Drip irrigation under mulch is ideal. Do not let the soil dry out and then soak it: the skin hardens in dry soil and the fruit may split when it suddenly gets a big drink.

Ease back on watering as the fruit approaches ripeness, in the last week or two. Heavy watering at this stage dilutes the sugar and gives watery, bland fruit, but do not let the vines wilt badly.

Feed with compost or a complete fertiliser at planting, then a liquid feed every two to three weeks while the vines run. Once fruit sets, switch to a fertiliser higher in potassium, which supports fruit and sweetness better than more nitrogen.

Pruning and care through the year

• Watermelons have separate male and female flowers on the same vine. Male flowers come first and drop off. Female flowers have a tiny striped melon behind the petals and need several bee visits for a full-sized, well-shaped fruit.
• If bees are scarce, hand pollinate early in the morning: pick a male flower, peel back the petals and dab its pollen onto the centre of an open female flower, or use a small soft paintbrush.
• Rest developing melons on straw, a board or a tile to keep them off wet soil, and turn them gently once or twice so they colour evenly.
• For bigger melons, let each vine carry only two to four fruit and pinch off later ones.
• On a trellis, support small melons in slings made from old stockings or netting tied to the frame, so the stems do not snap.

Harvesting

Watermelons do not ripen further once picked, so check for all the signs before cutting. The pale patch on the underside, where the melon rests on the ground, turns from white to creamy yellow. The small curly tendril on the stem nearest the fruit turns brown and dries. The skin loses its shine and turns dull, and the fruit gives a deep, hollow sound when tapped with an open hand.

Cut the stem with a knife or secateurs, leaving a short piece attached. Whole melons keep about a week or more in a cool spot; once cut, wrap them and keep them in the fridge for three or four days.

Growing in pots

Watermelons are not well suited to pots. If you only have a pot, use the biggest you can, at least 50 cm wide and deep, grow a small-fruited variety up a sturdy trellis, support each fruit in a sling, and water every day in hot weather.

Using it

Eat watermelon chilled, in fruit salads, with feta and mint, blended into juices and slushies, or frozen into icy poles. The white rind can be pickled.

Saving seed

Save seed only from open-pollinated, seeded varieties, not hybrids or seedless types. Take seeds from a fully ripe melon, rinse off the pulp, dry them on paper for a week or two and store them in a cool, dry place. Watermelons can cross with other watermelon varieties grown nearby.