Tomato ripening depends on temperature rather than sunlight

Gardeners often mistakenly believe that green tomatoes remain unripened due to a lack of sunlight or water. However, the primary cause of delayed ripening is temperature rather than light exposure.

The production of lycopene, the pigment responsible for the red color, occurs optimally between 20°C and 25°C. When temperatures exceed 30°C to 32°C during heatwaves, or when nighttime temperatures drop significantly, this biological process slows down. While the fruit may continue to grow in size, the thermal stress prevents the chlorophyll from degrading and transforming into red pigments.

Additionally, seasonal timing plays a role. According to the Société Nationale d’Horticulture de France, tomatoes typically require 45 to 60 days to mature from flower to fruit. Plants that bloom after mid-August may struggle to ripen before the first frost of autumn.