Why Does My Watermelon Have a Hollow Space in the Middle?

Cutting into a large, apparently healthy watermelon to find a crack or cavity running through the centre of the flesh — rather than solid, firm tissue all the way through — is a phenomenon called hollow heart. It is not caused by a pest or disease but by a physiological problem during fruit development. The melon is still safe to eat in most cases, though the texture and appearance are not what you hoped for.

What causes hollow heart

The hollow space in the centre of the melon forms when the outer flesh expands rapidly but the inner tissue cannot keep pace. This creates a crack that runs through the centre, typically appearing as a rough, dry-edged cavity or a star-shaped crack pattern. The most common causes are: large temperature swings between day and night during early fruit development (causing uneven growth rates), incomplete pollination (a well-pollinated melon with many viable seeds develops more uniformly than one with patchy pollination), and very rapid vine growth under heavy nitrogen feeding during fruiting.

Improving pollination quality

Better-pollinated fruit has more seeds developing evenly throughout the flesh, and seed development drives uniform flesh expansion. Block planting, hand pollination in small gardens and growing in warm, sunny conditions during the flowering period all improve pollination quality and reduce hollow heart incidence. Inadequately pollinated fruit — with few seeds — is much more prone to hollow heart than fully pollinated fruit.

Consistent temperatures during early fruit development

Hollow heart is more common in cool-climate growing where large day-night temperature swings are normal in summer. Growing under a polytunnel buffers temperature variation and reduces hollow heart incidence. In the open garden, this is difficult to manage directly — focus on variety selection and choosing an early-maturing variety bred for cool climates.

Is hollow heart watermelon safe to eat?

Yes. A melon with hollow heart is entirely safe to eat. The flesh in the rest of the fruit is normal in texture and flavour. Cut around the cavity, use the unaffected portions, and make note of the conditions so you can adjust next season.