Learning how to grow watermelon begins with plenty of warmth, sunshine and room for the vines to spread. Watermelon is a sprawling warm-season annual that can produce delicious fruit when given the right growing conditions.
South East Queensland gardeners can generally sow watermelon from spring into summer, provided there is enough warm weather left for the fruit to ripen. In cooler parts of Australia, wait until frost has passed and the soil is thoroughly warm before planting.
1. Choose the right position and soil
When deciding how to grow watermelon successfully, start with a position that receives at least six to eight hours of direct sunlight each day. The soil should be fertile, well drained and enriched with organic matter.
Work Rocky Point ActivGrow Soil Improver through the garden bed before planting, following the labelled application rate. Mounded rows can improve drainage in slow-draining soil, but they are not essential in every garden.
2. Sow watermelon seeds with plenty of space
Watermelons dislike root disturbance, so sowing directly into warm soil is often the simplest option. Sow two or three seeds approximately 2–3 cm deep, then keep the strongest seedling after germination.
Allow roughly 1–1.5 m between plants, with additional room for vigorous varieties. Compact, small-fruited varieties can be grown in a very large container or trained over a strong trellis. Support each developing fruit with a sling to prevent its weight from damaging the vine.
For more planting and training advice, see ABC Gardening Australia magazine’s guide to growing watermelon.
3. Water, feed and encourage pollination
Consistent moisture is an important part of how to grow watermelon, particularly while vines are establishing and fruit is swelling. Water deeply at soil level and avoid wetting the foliage late in the day.
Avoid deliberately drought-stressing plants in an attempt to make the fruit sweeter. Large changes between dry and wet soil can interfere with healthy growth. Feed according to soil fertility and product directions, avoiding excessive nitrogen, which can encourage leafy growth at the expense of flowers.
Male and female flowers grow on the same vine, with insects transferring pollen between them. Watermelons rely heavily on insect pollination, so encourage flower visitors and avoid spraying open flowers. Hand-pollination may help where fruit set is poor.
4. Know when to harvest watermelon
Most varieties take approximately 70–100 days or longer from sowing to harvest, depending on the cultivar and growing conditions.
Knowing how to grow watermelon also means recognising when the fruit is ripe. Look for several signs together, including a dried tendril nearest the fruit, a creamy yellow patch where the fruit rests on the ground and skin that has become duller.
A hollow sound when tapped can be another clue, but thumping alone is unreliable. Watermelons do not become sweeter after picking, so getting the timing right matters.
