Tomatoes not ripening: what to do?

In summer, tomatoes taste best from your own garden. But what do you do when the fruit does not want to turn red? Find possible reasons for tomatoes not ripening.

Many amateur gardeners eagerly await their tomato harvest but sometimes the little fruit just will not turn red. Even under optimal conditions, it can take two to three weeks for the tomato (Solanum lycopersicum) – which, by the way, is a berry botanically speaking – to develop its bright red colour. In addition to the colour, however, the taste also changes: the fruit gains significantly in aroma and sweetness over time.

A decisive factor for the development from green to red fruit to get rolling is the phytohormone ethylene. The plant produces this gas itself but needs a lot of energy to do so, mainly in the form of heat. Indeed, this is the crucial sticking point when nothing red is found on the tomato plant – even after a long wait: it is simply too cold.

Tomatoes not ripening: 4 expert tips

We show you below what alternatives are available to turn the green tomato fruits red.

• Tip 1: Create sources of ethylene
  The phytohormone ethylene promotes the ripening and reddening of tomatoes. If the tomato plants are planted in a small greenhouse, you can put fully ripe bananas or apples inside. These produce ethylene in large quantities. Thus, this somewhat accelerates the ripening of tomatoes.
• Tip 2: Feign dryness
  When the plants are fooled to think there is a drought, they panic and invest all their energy into turning the fruit red. However, this method should only be used towards the autumn because the tomato plant will not really grow or form new flowers and fruits.
• Tip 3: Tomatoes in plain paper
  If the time of the tomato plant in the garden has passed but there are still plenty of green tomatoes, they too can still be helped to turn red. Individual fruits can be wrapped in plain paper and placed in a warm place for post-ripening. Again, it helps if there is a ripe apple emitting ethylene in the immediate vicinity. This method is also useful when the fruits just do not want to turn red all summer. Once the fruits have reached the appropriate size, simply harvest them and store them indoors in a warm place wrapped in paper. Printed paper, such as newspapers, should not be used for health reasons (e.g. to avoid toluene in printing ink).
• Tip 4: Hanging tomatoes indoors
  If there are still plenty of green tomatoes on the plant in autumn, you can also cut off the entire plant. Then hang it upside down in a warm place indoors to dry, like a bouquet of herbs. Tomato fruits gradually ripen and can provide freshly harvested homegrown enjoyment in the garden for several weeks after the tomato season is over.

Why are tomatoes red?

On the one hand, the red colour serves to protect the tomatoes from extreme sun, but on the other hand to attract animals, which then eat the ripe fruit. The seeds are then in turn excreted and new plants germinate from them the following year. Thus, the reddening of the tomato is an elaborate mechanism for the preservation and propagation of its own species.