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Tomatoes, which by the way belong to the berries, taste best in summer. During the ripening process, the red varieties usually turn from an initial green to a juicy red. The red color is intended to protect against extreme sunlight, signal full ripeness and at the same time attract animals. But sometimes the fruit just doesn't want to turn red. This can have different causes, but can usually be remedied with a few small tricks.


It takes about eight to nine weeks from planting the seedling to the fully ripe fruit. The red coloring is the last development step of the tomato before harvest and usually lasts only a few days. For various reasons, this last step can be delayed or even omitted altogether.

Too low temperatures

  • Tomato plants need a lot of warmth
  • Look for a sunny location protected from rain
  • Do not plant outdoors before the ice saints
  • Frost fatal to plants and fruit
  • Greenhouse crops can get very hot very quickly
  • Adequate watering and ventilation is then particularly important
  • Temperatures that are too cold slow down the development of plants and fruit
  • Despite fruiting, red color occurs only slowly or does not appear
  • Fruits remain green and immature
  • Temperatures of at least 15 °C required outdoors
  • In the greenhouse, temperatures of more than 30 °C must be avoided

Too much leaf mass

Another reason for delayed ripening or the lack of red coloring of tomatoes can be too much leaf mass. Tomato plants are constantly producing new shoots and leaves. The more shoots and foliage they produce, the less energy they have to develop and ripen fruit. This can be remedied by regularly pinching out the plants, i.e. cutting out superfluous shoots. The clippings can then be left on the ground as mulch.

tip: The lowest leaves should generally be removed from tomato plants to counteract the dreaded late blight.

green collar disease

In the case of the so-called green collar disease, the ripening process is disturbed so that the fruit does not turn completely red. A circular, green stripe remains at the base of the stem, which is very hard, which also continues under the skin. The green is clearly distinguished from the red. The cause can be excessive solar radiation, temperatures above 30 °C, excessive watering, as well as a lack of potassium or an excess of nitrogen.
This disease can be avoided by lightly drying the plants in strong sunlight and heat shaded, does not fertilize with too much nitrogen and pays attention to an adequate supply of potassium and magnesium. A soil analysis in advance can be useful.

tip: There are varieties that are particularly susceptible to this disease, such as 'Harzfeuer', which should be taken into account when choosing a variety. Small-fruited cherry, panicle and bush tomato varieties are comparatively rarely affected.

ripening tomatoes

How the tomatoes still turn red

To speed up the ripening process in the greenhouse, you can hang up bananas or apples next to the plants, for example. These fruits give that ripening gas ethylene which can speed up the ripening process of the tomatoes. Tomato plants also produce this gas themselves, but they have to use a lot of energy to do this, for which they need a lot of heat and water. Another method is suitable for the greenhouse and for the bed.

  • You need a base, for example a wooden board
  • Place the board on the ground next to the plant in question
  • This is to prevent the fruit from touching the ground
  • Then twist the plant
  • Tomatoes should be on the board
  • Then put the mobile cold frame or cold box over the fruit
  • Also cover the bed with opaque fleece
  • Remove cover once a day to ventilate
  • Depending on the weather, fruits ripen within one to three weeks

tip: Even if the appetite for ripe tomatoes is great in summer, you should never eat unripe green tomatoes because they are poisonous, with the exception of special green varieties. The solanine content in unripe fruit is so high that it is harmful to health.

reduce pouring amount

Withdrawing water can encourage plants to encourage fruit ripening. However, you shouldn't start before autumn. As long as the plant is growing and producing fruit, it needs a regular and plentiful supply of water.

In autumn, when the fruits have reached their final size and do not really want to turn red, you extend the intervals between the individual waterings and only water about every three days. The reduced water supply should signal to the plant that its growth is complete. Consequently, they put all their energy into the ripening process of the fruit.

reduce light

The deprivation of light is similar to dehydration. As long as the tomato plant is growing and developing fruit and seeds, it cannot do without sufficient light. As soon as the fruits are fully grown, they get by with significantly less light, because the light intensity hardly plays a role in the red coloring of the fruits. They can even turn red in complete darkness. To speed things up, you can put tomatoes in a pot or tub in a shady place and cover the plants in the bed with plant fleece.

Pick the greens and let them ripen indoors

It often happens that the tomato season in the garden is actually over, but many fruits are still green. Before the frost kills them, you should harvest them and let them ripen indoors. They are best harvested when temperatures consistently drop below 10°C.

  • Always harvest unripe tomatoes with the stalk
  • Without a handle, cracks may form at the base of the handle
  • Cracks are entry points for germs
  • Mold often forms on the cracks, which spoils the fruit
  • Green tomatoes ready for ripening should not show any damage
  • Check fruit for brown spots, risk of brown rot
  • Tomatoes can also ripen on the plant
  • To do this, cut off the entire plant
  • Hang the tomato plants upside down in a place with a temperature of 18-20 °C
  • Room with high humidity, for example in a basement
  • Light for post-ripening not required
  • Typical red color appears within the next few weeks

Individual fruits can be placed in flat fruit boxes and stored in a suitable place. If possible, the tomatoes should not be on top of each other and should be checked regularly for damage or rotten spots and the corresponding fruits should be sorted out. If you want, you can put an apple in the box and use the ripening gas that flows out for the ripening process.

Alternatively, the green, unripe fruit can be wrapped in newspaper, placed in a shoe box, or simply placed in a bowl, covered and stored in a warm room until red. Gradually the fruits turn red and can be eaten. As a rule, these measures do not reduce the taste or aroma of the ripe fruit.

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