Why Is My Watermelon Not Ripening on the Vine?

The watermelon has been on the vine for weeks, it is large and impressive, but it does not seem to be ripening — the skin still looks green and fresh, it sounds hollow but you are not sure, and the tendril near the stem is still green. Watermelon ripening is a slow, heat-dependent process that cannot be rushed by picking early. Getting the timing right — and knowing how to tell whether a melon is actually ripe — is one of the most skill-dependent parts of growing watermelon.

Not enough heat accumulated since fruit set

Watermelon takes 70–90 days from transplanting and roughly 35–50 days from the moment of fruit set (when the female flower was pollinated) to reach full ripeness, depending on variety and temperature. Cool summers, overcast periods and nights below 15°C all slow the ripening clock. In the UK and northern Europe, watermelon often needs a cold frame, polytunnel or glasshouse to ripen reliably. If the summer has been cool, your melon may simply need more time than the variety's stated "days to maturity" suggests.

How to tell if a watermelon is ripe

Use several indicators together rather than any single check:

• Tendril test: the small curly tendril closest to the fruit stem dries up and turns brown at full ripeness. A green or only slightly dried tendril means the melon is not ready.
• Ground spot: the area where the melon rests on the soil turns from white-green to a buttery yellow at ripeness.
• Skin dullness: the skin loses its shine and becomes slightly dull as ripeness approaches.
• Sound: a ripe watermelon sounds dull and hollow when thumped with a knuckle; an unripe one sounds higher-pitched and dense.

Too many fruit competing for ripening energy

A vine carrying four or five fruits will ripen all of them slowly. For the fastest ripening and best flavour, limit each vine to two fruits in cool climates, removing any additional fruitlets when they are the size of a tennis ball. This channels the plant's energy into fewer, better-quality melons that ripen faster.