Growing Watermelons in Tasmania

These delicious, juicy fruit are a real treat to grow in the garden. They need a long, warm growing season to really thrive, so they’re not ideally suited to the Tasmanian climate. If you’re wanting to grow some, it’s best to choose smaller varieties which mature more quickly and don’t need such a long growing season. Heritage varieties that were originally bred for colder climates tend to do better in Tasmania.

Like other members of the cucurbit family, (think pumpkin, squash and cucumbers) they grow on long trailing vines. They take up a lot of space and can be hard to fit into a small home garden, but if you have the space for them, they can be a rewarding and exciting crop.

There are many varieties available in a myriad of shapes, sizes and colours. As is the case with most plants, only a few varieties are available as plants and from gardening centers, but if you buy seeds online, you’ll find a great assortment of shapes, sizes, colours and flavours. If you’re low on space or plan to grow your melons vertically, then the smaller varieties are a good choice. Watermelons can get really big and heavy and need a lot of support and a strong trellis to be grown vertically.

They’re a thirsty crop and will use water all season long. Limiting their water right at the very end of the growing season will make the fruit sweeter.

Don’t-over water your plants while the fruit is ripening. The sugars develop better with a little less water.

They really do need full sun and should not be grown in a partially shaded spot.

Watermelons like a rich, well-draining soil. They have a deep, fine root system, so the soil needs to be nice and loose for those delicate roots to really spread out and suck up all the water and nutrients that they need to support such big, hungry vines. Work in plenty of compost and well-rotted manure before you plant. They’re nitrogen-hungry, so you can even add some organic, slow-release fertilizer to the soil before planting.

Seeds can be planted into the garden once all danger of frost has passed and it's consistently warm. They need a long growing season, so try to get them in as soon as its warm enough.

Seeds can be started in trays or sown straight into the garden. If you look at the seeds, you’ll notice that they have a pointy end and a more rounded end. For best germination, the seeds need to be planted with the pointy end facing down into the soil. Make sure the seeds are well covered and press the soil down gently. They usually germinate quite quickly and the seedlings are large and easy to spot. Remember to keep the soil moist. Watermelons are traditionally grown on mounds to help with drainage.

Seedlings can be planted into the garden as soon as all danger of frost has passed and and it's consistently warm. Try to get them in earlier rather than later to make the most of the short growing season.

Watermelons don’t like to have their sensitive roots disturbed, so handle them with care when you’re planting them out. Add a small amount of bonemeal to each hole before planting. It’ll help them develop strong roots systems to feed their hungry vines and produce big juicy fruit. Remember to give them extra attention for a week or two after planting and make sure that the soil stays moist. Watermelons are traditionally grown on mounds to help with drainage.

Pinch out the growing tips when the vines are about 2m long. This really helps if you’re short on space and encourages your plants to put more energy into the existing fruit.

Once the fruit start to grow, it’s a good idea to put something (like a piece of cardboard or plastic) under the them. This helps prevent damage to the bottom of the fruit while it ripens.

Water deeply and regularly while the plants are setting fruit. Watermelon plants are prone to powdery mildew, so try not to wet the leaves while watering. In the last two weeks before the fruit is ripe, reduce the amount that you water considerably. Less water during this last stage will give you sweeter fruit. The plants often wilt in the heat of the day, but if they’re wilting in the cooler parts of the day, it’s a sure sign that they need water.

Watermelons are hungry plants and appreciate regular feeding. They’ll appreciate a balanced feed like worm tea or a balanced organic fertilizer every 3 weeks.

Mulching helps to keep the soil moist and the weeds out. Apply a generous layer of organic mulch such as lucerne, sugar cane or peastraw. As they grow, they become so vigorous, that they start crowd out any weeds and shade the soil, effectively becoming their own mulch, at this stage it isn’t really necessary to keep topping up their mulch, but it won’t do any harm either.

There are three sure signs that your watermelons are ready to harvest.

1. The bottom of the watermelons start to turn yellow.

2. They sound hollow when tapped.

3. The tendril closest to the fruit you’re harvesting is brown and dry instead of the usual green and supple.

As soon as they’re showing signs that they’re ripe, you can begin to harvest them. Harvest in a similar way to pumpkins, cutting the fruit away from the vine with a sharp knife. Watermelons won’t ripen any further once they’ve been picked, so make sure they’re ripe before you harvest them. They’re best eaten soon after they’re picked, but depending on the variety, can be stored for up to 2 weeks. Use the fridge to chill the fruits before eating, but not for storage. Uncut watermelons stored in the fridge will deteriorate more quickly than those stored at room temperature.