How to grow & care for watermelon
Watermelons grow on sprawling vines during the warmest months of the year in Australia. These sun-loving plants can be left to grow along the ground or the smaller varieties, with petite fruit, can be trained up a sturdy trellis. And if you’re short on space they can be grown in large pots.
Watermelons come in a range of varieties with different shaped, sized, and coloured fruit. Watermelon flesh isn’t always red - it can also be orange, white or yellow depending on the variety. Some varieties produce fruit that can be up to 10kg heavy, while others grow smaller fruit weighing in at around 2kg each.
Watermelons are not frost tolerant and they love hot, dry climates. In cooler climates watermelons should be planted out in spring, so long as the risk of frost has passed and the soil has warmed to around 18-22°C. Look for varieties with a faster maturity date, because many need 100+ days from planting before harvesting.
In warm and tropical regions watermelon can be grown year-round - look for varieties that are more tolerant of humid conditions if growing during the wetter seasons.
Top 5 steps to growing watermelon
- Choose a full sun position in your garden or grow in large pots.
- Varieties of watermelon with smaller fruit can be grown up a sturdy trellis or in large pots.
- Improve the soil before planting by adding Scotts Osmocote Compost Premium Soil Improver and Scotts Osmocote Plus Organics Tomato, Vegetable & Herb Plant Food & Soil Improver.
- Protect newly planted watermelon seedlings from pests like snails and slugs using Defender Slug & Snail Pellets
- Watermelon seeds can be sown in small pots or punnets and raised indoors in cooler climates before planting out into prepared soil once the weather warms up. Watermelon seeds need a warm soil temperature between 18-22°C to germinate - so use a heat mat if needed.
- Watermelon seeds or seedlings
- Scotts Osmocote Compost Premium Soil Improver
- Scotts Osmocote Plus Organics Tomato, Vegetable & Herb Plant Food & Soil Improver
- If growing in pots, Scotts Osmocote Plus Organics Premium Potting Mix and a suitable pot
- Garden trowel
- Trellis or sturdy support structure if you want to grow watermelons vertically
- Defender Slug & Snail Pellets
- Defender Pyrethrum Insect Spray
Watermelon can be grown from seeds or seedlings, in a full sun spot. Watermelons prefer a rich, moist but free draining soil. So prepare the soil by mixing Scotts Osmocote Compost Premium Soil Improver and Scotts Osmocote Plus Organics Tomato, Vegetable & Herb Plant Food & Soil Improver - through the top 15-20cm of soil before planting.
If you’re growing watermelons vertically, set up the trellis or support structure - before planting to avoid disturbing the roots later on.
Planting in the garden
Growing from seedlings
Plant watermelons about 80-100cm apart (depending on the variety) into prepared soil - you may want to allow a larger spacing if you live in a particularly humid climate, this will allow better airflow around the plants and help prevent fungal diseases. Lightly mulch the soil around plants after planting with an open organic mulch to retain moisture.
Plant seedlings into mounds to improve drainage if needed in your garden.
Protect small seedlings from slugs and snails using Defender Slug & Snail Pellets .
Growing from seeds
Watermelon seeds can be direct sown in warmer climates, but in cooler climates you can start them indoors to get them growing if outdoor conditions aren’t quite right yet.
Directly sow watermelon seeds 1-2cm deep in clusters of 2-4 seeds, allowing 80-100cm between clusters. Once the seedlings germinate thin to the strongest seedling in each cluster by removing the weaker seedlings. If starting indoors sow the seeds into punnets or small pots filled with Scotts Osmocote Plus Organics Premium Potting Mix - sow 4-6 seedlings per punnet.
Keep the soil moist, but not soggy while the watermelon seeds germinate which will take 6-10 days.
Mulch around direct sown seedlings when they are 5-10cm tall to retain moisture and protect young seedlings from slugs and snails with Defender Slug & Snail Pellets .
Punnet or pot sown watermelon seedlings should be planted into the garden when the soil has warmed and the risk of frost has passed.
Planting in pots
Watermelon can be grown in large pots that are 40-50cm deep and the same wide. Fill the pot with Scotts Osmocote Performance Naturals Potting Mix and install a support trellis or position the pot near a sturdy wire fence. At the base of the trellis sow seeds (plant 3-4 seeds and thin to the strongest once they have germinated) or plant a single seedling.
Protect young watermelon seedlings from slugs and snails with Defender Slug & Snail Pellets. Mulch around your watermelon plants to retain moisture.
Care & Harvest
Fertilise your watermelon plants 30-50 days after planting a s the vine begins to sprawl out and flowers develop. Apply an organic based fertiliser like Scotts Osmocote Plus Organics Tomato, Vegetable & Herb Plant Food & Soil Improver, at the recommended rate around the main stem / root growing region of the plant.
To improve the quality and flavour of your watermelon harvest, it’s best you only allow each plant or vine to produce 3-4 fruit. So once 3-4 healthy fruits have begun developing, pinch out the growing tip of the vine to encourage energy into the remaining fruit.
Depending on your climate and the variety you’ve chosen, your watermelons will be ready for harvesting around 80-100 days after planting. Watermelons that are ready to pick when you notice the skin changes from shiny to dull and the area that touches the ground turns from white to creamy/yellow. Use scissors to carefully cut them from the growing vine, leaving any unripe melons to continue growing.
Pests & Diseases
Slugs and Snails will cause significant damage to young watermelon seedlings. Protect your crop by setting beer traps (saucers filled with beer) or use Defender Slug & Snail Pellets.
To reduce the chance of fungal disease infecting bean foliage, avoid overhead watering and if you live in a region with high humidity, choose a variety that tolerates humidity and make sure there is plenty of airflow between plants.
Watermelons are also susceptible to aphids, spray any infestations with Defender Pyrethrum Insect Spray.