The secret behind seedless watermelons: This is the trick to growing the fruit without seeds

On a hot, balmy summer’s day, nothing beats biting into a chilled, juicy wedge of watermelon - as well as hydrating you and helping to cool you down, it’s healthy, packed with vitamins, antioxidants (lycopene) and fiber. Watermelon is also very versatile - apart from eating raw slices, you can make a tasty fruit salads, smoothies...

For many watermelon lovers, the only inconvenience is the seeds. Although they’re perfectly safe to eat, it’s the only real downside - especially having to chew on or spit out the hard, black seeds. There are over 1,000 varieties of watermelon - including seedless ones, which removes that problem.

As August 3 is National Watermelon Day, let’s take a look at how the seedless variety is cultivated.

Seedless watermelons first came onto the market more than half a century ago. To say that they are all completely seedless isn’t strictly true - most tend to have few seeds - the mature black ones or the flat white ones which have not fully matured, while some may have none at all.

Cross fertilization

The seedless variety have a hybrid, triploid seed, which is produced by crossing a diploid variety (with two sets of chromosomes) with a tetraploid plant (four sets of chromosomes). The process involves crossing male pollen for a watermelon, containing 22 chromosomes per cell, with a female watermelon flower with 44 chromosomes per cell.

When the fruit matures, the small, white seed coats in the flesh contain 33 chromosomes, making it sterile and effectively unable to produce seeds.

Seeded and seedless watermelons are sometimes grown together but the seedless variety are far more popular with consumers, making up 92% of all watermelon sales. Watermelon season runs from May through September, and July is the month when they are at peak ripeness.

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