How to plant, grow and harvest watermelon

One of the most popular summer fruits, watermelons are surprisingly easy to grow at home.

What you need to know about watermelon

Name: watermelon (Citrullus vulgaris and/or C. lanatus and cvrs.)

Plant type: fast-growing herbaceous annual creeping/running “vine”

Height: less than 500mm, with spread of 2m+

Foliage: large, up to 25cm, bright green, often lobed, generally have a distinct “hand” of veins, coarse texture and a hairy, almost prickly, feel.

Climate: tropical, sub-tropical; warm and cool temperate if planted in the right location.

Soil: well-drained sandy loam with added manures or compost.

Position: full sun; will tolerate a little wind.

Flowering and fruiting: yellow flowers followed by large, round to oval-shaped fruit with sweet, moist red, pink or yellow flesh.

Feeding: feed at planting and apply liquid organic products during growth and fruit development.

Watering: although drought tolerant, best growth and fruiting comes with reliable moisture.

watermelon

Appearance and characteristics of watermelon

Who doesn’t love watermelon? The enormous, delicious, almost crunchy fruit drips with sweet, refreshing juice. Cold from the fridge, added to fruit salad or even juiced, poured over ice and topped with a sprig of mint—does it get any better or more summery than that?

Watermelon is an interesting plant. As the name implies, it is incredibly juice-filled, yet it originally hails from very dry regions, and will in fact grow in near-drought conditions. The watermelon is great fun, and very rewarding to grow at home. Thanks to hybridising there are even varieties that can be grown in smaller gardens, and even in large pots.

Watermelon has a creeping, scrambling form similar to that of other melons. The large leaves are quite distinctive. They are held upright on succulent stalks and tend to have an almost-prickly hairiness. The leaves have a very coarse texture. At the base of the leaves you’ll find coiled-up tendrils of the sort found on true climbers. If a watermelon encounters something as it grows, such as a small shrub, it will use these tendrils to help it scramble over the object. Wayward shoots may head off up a tree, too.

There is quite a range in the colour of the fruits. They are generally a deep green with patchy, lighter coloured stripes, however some are near black, with circular golden patterns, as well as other forms.

The fruit can be enormous—around 10kg is not uncommon, and sizes of 45kg or more have often been recorded!

Plants can be quite sprawling, so select the variety carefully. Each plant should produce four or more fruit, however you’ll need to follow some tips to get the best yield. Watermelons are very fast growing given the right conditions, and harvest can be in as little as 10 weeks from planting.

Uses for a watermelon plant

Watermelon is grown solely for its fruit.

Preferred conditions for watermelon vines

Sunlight

Watermelon needs full sun.

Aspect

Watermelon will tolerate a little wind, however leaves and stems will easily be broken by very windy conditions.

Soil or potting mix

Watermelon can perform very well in sandy, gravelly and otherwise dry soil, however the best performance comes from quality soil with good drainage that’s been improved with organic matter.

Temperature considerations

Watermelon plants are natives of hot, dry regions. They will not tolerate any frost. They can be grown in virtually any region, provided you get the timing right when planting them. If you are in an area prone to frost, your watermelon cannot be planted until all fear of frost has passed. As it is fast growing, you will get a crop from your plant before the weather cools down again. In cooler zones, plant in the warmest, most sheltered spot you can find.

Planting watermelon

When to plant watermelon

Watermelon seedlings prefer soil temperatures from 21–35°C. Sow in seed trays in August, and transplant seedlings from October to December.

Pollination and fruit production

Watermelon requires the presence of both male and female flowers to produce fruit. Sometimes a single plant will carry both, other times not. To ensure good levels of pollination, and therefore fruiting, your best bet is to put in at least two plants—they can be in the same hole.

If you plant a number of plants a few weeks apart, you can extend your harvest period from late spring through until early winter or first frost, whichever comes first.

Seeds and seedlings

Watermelons, like most melons, can be very fussy about root disturbance, so if planting from seedlings, take care not to disturb the roots when transplanting. If you are growing from seed and not doing so in-situ (for example, if you’re starting them in a greenhouse in a cooler climate), it’s best to raise them in peat-type pots, as this means the entire pot can be planted without any root disturbance.

Soil preparation

Blending through quality compost or well-composted manure will dramatically improve growth and overall performance. Add a controlled-release fertiliser for fruiting plants at planting time, too.

Caring for watermelon

Watering

Watermelon is drought tolerant, but the best growth and fruiting comes when the plant has reliable water during active plant growth and fruit development periods, especially in the height of summer.

Feeding

Regular liquid foliar applications of seaweed or fish-based products will improve flower and fruit production. Until the plant starts flowering, supplementary liquid feeding with a product high in nitrogen is beneficial.

Avoiding root disturbance

Avoid any digging or scratching in the surface soil around the root zone. You can all but remove the need to do so by keeping weeds down. The best way to do this is with a good layer of a quality mulch, such as lucerne or pea straw.

Pruning watermelon vines

Refer to information specific to your variety for pruning tips. Some varieties are best left unpruned. Others should have the first round of flower buds removed, or have their early shoots reduced.

When to harvest watermelon

When to pick a watermelon can be a very difficult thing to work out if you’ve never grown them before. The general consensus among experienced growers is to wait until the fruit is fully coloured, then roll it over. If the area in contact with the ground is starting to yellow, then it is likely ripe. Another way to check for ripeness is to tap the melon. If you hear a deep, dull sort of thump, it’s ripe. You should also find that the stem connecting the fruit starts to shrivel when the fruit is ripe.

Diseases and pests

The most common problem with watermelon is the same one most melons suffer from—powdery mildew. Some growers say regular applications of seaweed-based products can help avoid the problem, otherwise there are many suitable food-safe organic options for treatment. They are very effective, but make sure you treat the problem as soon as you notice it, and treat the entire plant, even if the problem is only visible on one section.

Watermelon propagation

Being annuals, watermelons are grown from seed. You’ll find an excellent range available, from traditional to hybrid miniature forms.

Seed should be sown directly into the area where the plants will grow. Put a few seeds in each hole and, as they develop, prick out the weaker ones.

If growing in pots or trays, plant in a quality seed-raising mix and keep warm, ensuring they are protected from frost. When planting out, avoid root disturbance.

Seedlings can be prone to fungal problems, so watch them carefully, and treat as required with a fungicide.

If you like this then try

Mango: if there’s one fruit that says “summer” it has to be the mango. It is a surprisingly easy, and potentially very rewarding, fruit tree to grow.

Olive: a fruit tree that thrives in dry conditions, an olive makes a handsome landscape plant, too.

Mint: the perfect garnish for a fruit salad or refreshing summer juice, mint is super easy to grow. 

Start planting today

Check out our huge range of plants now and get your garden growing!

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