How to Grow Watermelon

Being 92% water, there’s no prizes for guessing how watermelon got its name!

It will also come as no surprise that it is commonly associated with hydration due to its water content but did you also know that it contains vitamins A, B6 and C, potassium, magnesium and lycopene? These qualities mean it can be helpful improving heart health, reducing inflammation, preventing macular degeneration, relieving muscle aches, aiding skin health and digestion and fighting cancer cells. If you are in a warmer climate, you should find watermelon relatively easy to grow.

When to grow watermelon

Watermelon likes soil temperatures of 27-32°C or 80–90°F to germinate from seed and doesn’t respond well to frost. For this reason, if you are in a warmer climate with mild winters, planting in spring and growing through summer is ideal. For colder climates, you’ll want to ensure you find a variety that is more suited to colder climates and more frost tolerant.

Watermelon varieties

There are over 1200 different varieties of watermelon grown around the world. Here are a few that you might like to try:

· Charleston Grey – a classic oblong shaped variety with green skin and pink flesh with fruit weighing up to 15Kg each with a sweet flavour

· Sugar Baby – a dark green skin and pink flesh with a more spherical shape weighing up to 4Kg each with an exceptionally sweet taste. Drought resistant and great for cooler climates

· Mountain Sweet Yellow – elongated fruit weighing up to 10Kg with a dark green and light green striped skin and yellow/orange flesh that is very sweet with a honey-like flavour

· Seedless F1 – a non GMO hybrid variety created to produce large seedless fruit with a green skin and pink flesh weighing up to 10Kg each

· Moon and Stars – an heirloom variety with large fruit sporting dark green skin with yellow “stars” and a sweet red flesh

How to grow watermelon from seeds

If you want to grow your watermelon seeds out in trays first, you absolutely can but they can sometimes not transplant too well so if you have the time and space to direct sow instead, that would be the best way to go about it.

If you are direct sowing, you’ll want to space your plants well apart as these plants like to wander and expand!

You’ll need a sunny spot that gets at least 6-8 hours of sunlight per day and well-draining soil as watermelon does not like to be waterlogged. Creating a soil mound to plant your seeds in can be a good idea to help with drainage. It’s also a good idea to mulch the mound to help keep the moisture in and protect the vine from drying out.

It can be a good idea to plant a few seeds together to compensate for any poor germination and then if they all sprout, you can thin them out later.

How to grow watermelon from seedlings

If you are transplanting seedlings then you’ll want to ensure you space the plants around a metre or just over 3 feet apart so they have room to spread out. Lightly water the seedling in with a seaweed solution such as the Plant Doctor’s Seaweed Secrets (use SSME10 for 10% off your order) to minimise transplant shock.

In order to set fruit, the flowers will need to be pollinated. Just like pumpkins and zucchinis, watermelons have male and female flowers. The female flowers are the ones that produce the fruit but they only do so if they have been pollinated by the male flower. Bees and ants along with other beneficial pollinators are your best friend here but you can always give them a helping hand by picking the male flowers and ensuring the pollen gets into the female flower.

You’ll want to ensure you keep watering your vines regularly at the base because being 92% water, they will need plenty of it, however when the fruit has reached it’s full size, you don’t want to be watering too much as this can cause the fruit to burst, just like pumping air into a balloon, there is a limit to how big it will grow!

Pruning may be important if overcrowding is becoming an issue. Overcrowding can lead to disease and pest impacts.

How long does watermelon take to grow?

Most varieties of watermelon will take around 70-100 days to reach full maturity but look at the individual varieties that you choose to grow as some can take more or less time.

When to harvest watermelon

There are a few different ways to work out if your watermelon is ready to harvest. Similar to a pumpkin, you can tap the watermelon to listen for a sort of hollow sound.

Depending on your variety, the skin may tell you what you need to know. If the skin looks shiny, it is probably not quite ready yet but if the skin starts to look a bit dull, that could mean it’s ready to harvest.

Lastly, the sure fire way to tell if your watermelon is ripe is to look for the tendril that is on the vine right next to your watermelon. If that tendril has gone brown and shrivelled then it is time to harvest!

Watermelon pests and diseases and how to control them organically

Downey Mildew

Downey mildew is in fact a parasite that is recognisable by yellowing or bleached spots on the top side of leaves and a white mould on the underside of the leaves. Cool and moist weather is when the mildew thrives so ensuring you have plenty of space between plants to allow air flow and watering at the base of the plant rather than overhead will help. Remove any infected leaves as soon as possible and ensure you rotate your crops to avoid future problems.

Powdery Mildew

If you find a powder-like substance on the leaves of your watermelon vine, it is likely to be powdery mildew which is caused by a bacteria that loves hot, humid weather. The great news is that there are a few natural remedies that work well to stop the spread of it. Firstly, you want to water your plants at the base of the stem and avoid getting the leaves wet. Then you can try spraying the affected areas with a water and milk solution (1 part milk: 2-3 parts water), or mix 2-3 tablespoons of apple cider vinegar with a gallon or 4 litres of water and spray the affected leaves. There are other options including hydrogen peroxide, potassium bicarbonate, or copper too. Alternatively, you can use neem oil or another organic fungicide to treat it.

Fusarium Wilt

A disease caused by fungus is wilt. The fungi live in the soil then work their way into the plant through the root where they begin to cut off the vessels that the plant uses to transport water to other parts of the plant. As a result, the leaves begin to wilt and eventually die. There’s no way to cure wilt but there are a few ways you can prevent it from becoming a problem in the first place. Start with disease resistant varieties of watermelon and ensure you use well-draining soil (raised garden beds are ideal for this). Don’t overapply nitrogen fertiliser as this may increase the susceptibility of your soil to fungus and avoid planting in garden beds that have had a problem with wilt previously. As with all fungal diseases, water plants at the base of the plant and not on the leaves.

Squash Mosaic Virus

Squash mosaic virus is a hard one to spot as a plant can seem more or less healthy but if you see mottling of maturing fruits, leaves that cup upwards or develop irregular patterns, blisters or unusual swellings on the fruit then you may have a problem with squash mosaic virus. The virus is more commonly in the seed which is why many curcubit seeds you see for sale have been treated to prevent it. Cucumber beetles are also known to spread the virus. If you find this disease on your plants, don’t muck around trying to solve the problem – the only real solution is to remove the plants and burn them to avoid it spreading elsewhere.

Marks top tips for growing watermelon

Try growing your watermelon vines over a trellis to encourage air flow and help to keep the fruit from resting on the ground where it is easy for pests to access and may be susceptible to rot. It can also be used to shade other plants that may find direct summer sun a little too harsh.

Do you have any tips or questions about growing watermelon? Mark and the Self Sufficient Me team love hearing about your growing success so why not join our forum to let us know how you went growing watermelon?

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