There really cannot be that many people who don’t like watermelons. For sheer eating pleasure a cool, juicy slice of watermelon on a hot day is difficult to beat. 

Sweet and delicious, the fruit contains vitamins A, B6 and C and a significant measure of lycopene, a phytonutrient, good for heart, bone and prostate health. The anti-oxidants in watermelon maintain the body’s cells and protect against cancer.

Fat-free and low in calories, the fruit that scores high on weight-loss diets. And since watermelon is about 92% water, it is a great way to hydrate when temperatures are high.

RISING TO THE CHALLENGES

Watermelons like the heat. They need a 3-month, warm weather growing season. As a crop, watermelon can be a little tricky, but it is rewarding if you do it properly and has good market potential.

Doug Simmons, one of the most informed and talented crop specialists I have encountered, used to say that tricky crops really taught people to farm. The challenge, he would tell me, is in learning to scan your fields daily with informed eyes so that you notice, and can deal with, problems before they take hold.

The rewards are twofold he told me – nothing excites a crop farmer quite as much as the sight of a healthy, growing crop and, come harvest, good yields are satisfaction for the soul and money in the bank.

ANOTHER AFRICAN WINNER

An African native, watermelon is an annual, ground-trailing vine with large, lobed, dark green leaves and the striking fruiting bodies, now familiar to fruit lovers worldwide. Other popular members of the same family (Cucurbitaceae) are squash, pumpkins and cucumbers.

The sexually separated, yellow flowers occur on the same plant. Male flowers appear at leaf nodes on the main stem and females show up on secondary stems a week after their masculine counterparts.

After fertilisation, when they have done their work, male flowers drop off and fertilised female flowers develop the fruit.

There are many different shapes (round to oval), weights (4 kg to 40 kg, or 9 lbs to 90 lbs) and colours (dark green with yellow stripes, through light green to grey green), and a wide range of varieties, for small-scale farmers to choose from.

Testing the market is always a good idea unless you are absolutely certain of demand. You could start with a small patch of watermelon vines before committing to a bigger investment in a larger field.

PLANT PRODUCTION

Soil

• Watermelon plants like well-drained, slightly acidic (pH 6 to 6.5) sandy loam soils. (Let’s face it most plants like well-drained, sandy loams.)
• Good drainage is really important because the vines and the fruit are on the ground.
• Moisture hanging around on the soil surface under the leaf canopy is just what insects love. To stop the bugs in their tracks, you want to get the water away from the surface and into the soil profile, as fast as possible.
• Improve drainage that’s not up to scratch by adding plenty of organic material like compost and well-rotted manure.

Temperature

• Temperatures between 21°C and 32°C are good for germination and growth.
• There is no germination below 16°C.

Cultivation

• There is no need to pulverise the soil.
• Minimum-till cultivation is easier on the input budget and remediates deconstructed soils that have been stripped of their nutrients.
• Weed the field diligently during land preparation, then weed again before planting.
• Grow the vines on well-composted mounds about 30 cm (1 ft) high and ½ m-1 m (2 ft to 3 ft) wide.
• Read up your specific variety requirements to work out the distance between mounds which is generally between 1.2 m to 1.8 m (4 ft to 6 ft).

Also read: Conservation agriculture: Do cover crops dry out soil?

Irrigation

• Water the planting area to field capacity.
• Field capacity is the smart way of describing soil that is “full but not overflowing” or properly wet, but not waterlogged.
• Watermelon needs water throughout the season, but especially during the first month, again when the fruit is setting and growing, and during the last 2 weeks before harvest.
• Obviously, a plant that supports fruit with a 92% water component will need a lot of water, but overwatering will also stress the plant and dilute the sugars.
• Learn from other successful growers and keep your eyes on your crop.
• Water once or twice a week.
• Water deeply, so that it goes down to at least 15 cm (6 inches), and apply the water at ground level.
• A drip irrigation system is ideal, but laying down hoses or watering by hand is a viable alternative, as long as the watering is on the ground and there is no splashing.

Also read: Watering vegetables: Use water wisely

Planting

• Plant seeds into thumb-shaped planting holes 1.3 cm (1/2 inch) to 2.5 cm (1 inch) deep and plant at about 6 to 8 seeds per mound.
• Some watermelon growers, especially those who prefer to plant the shorter season varieties, like to use plastic as a ground cover. It keeps soil temperatures up and controls weeds.
• Minimising contact with the soil surface helps prevent insect damage on the fruit.
• If you decide to go this route, cut slits into the plastic and plant into the slits.
• Germination times vary between 5 and 10 days.
• Watermelons are seriously averse to having their roots disturbed.
• When you thin cut the weaker seedlings off at ground level once they are about 5 cm (2 inches) tall.
• Leave behind the 2 or 3 strongest seedlings.
• If you aren’t using black plastic mulch, woodchip and straw mulches are also good for weed control and moisture conservation.
• Only mulch about 5 cm to 7 cm (2 inches to 3 inches) around the plant once the seedlings are established.
• Never cut back, or pinch out, leaf growth on the vine.
• The leaves are the production power houses of the plant.
• Left undisturbed, they will do a fine job of supplying necessary nutrients to the growing fruit.
• Keep on top of weeding until there is enough cover from the leaf canopy to shade out the dreaded weeds.
• When the fruit gets bigger, lifting it off the soil with a layer of cardboard or straw will help to stop rotting and insect damage.

Harvest

• From about day 75 look for signs of harvest readiness on ripening fruit:
• The spot where fruit rests on the ground yellows; leaves and tendrils near the fruit change from green to yellow and brown.
• If you pick up the watermelon and thump it you will hear a hollow sound.
• If you squeeze it you will hear a crackling sound, the skin is rough to the touch and the surface colour dulls.
• Early morning is the best time to harvest.
• The cooler you can keep the fruit the less moisture it will lose and the longer it will keep without over-ripening.
• Cut, rather than pull, the stem at 2 cm to 4 cm (1 inch to 1.5 inches) above the fruit with a clean knife or a pair of pruning clippers.
• Keep the harvested fruit in the shade and store it in a cool place before you market it.

References and resources:
Google books – The visual food encyclopaedia
http://ownyourfarm.blogspot.co.za/2015/12/how-to-grow-organic-watermelons.html
https://adesolayinka.wordpress.com/2017/02/02/tips-on-water-melon-farming-in-zambia/
https://www.agricultureinzambia.com/how-to-grow-watermelons/
https://www.starkeayres.co.za/com_variety_docs/Watermelon-Production-Guideline-2014.pdf