Why do my tomatoes not turn red? What you can do now

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

Causes

From planting the seedling to the fully ripe fruit takes about eight to nine weeks. Reddening is the last stage of tomato development before harvest and usually lasts only a few days. For various reasons, however, this last step may be delayed or even omitted altogether.

Too low temperatures

  • Tomato plants need a lot of heat
  • Ensure a sunny location, protected from rain
  • Do not plant outdoors before the Ice Saints
  • Frost is deadly for plants and fruits
  • In greenhouse crops, it can get very hot very quickly
  • Sufficient watering and ventilation then especially important
  • Too cold temperatures slow down development of plants and fruits
  • Despite fruit formation, red coloration occurs only slowly or remains absent
  • Fruits remain green and unripe
  • Outdoor temperatures of at least 15 °C required
  • In the greenhouse, avoid temperatures higher than 30 °C at all costs

Too much leaf mass

Another reason for delayed ripening or failure of tomatoes to turn red can be too much leaf mass. Tomato plants constantly form new shoots and leaves. The more shoots and foliage they form, the less energy they have to form and ripen fruit. This can be remedied by regularly pulling out the plants, d.h. Cut out superfluous shoots. The cuttings 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 fruits do 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 clearly distinguishes itself from the red. This can be caused by too much sunlight, temperatures above 30°C, too much watering, and potassium deficiency or nitrogen excess.
This disease can be avoided by providing the plants with light shade when they are exposed to strong sunlight and heat, by not fertilizing too heavily with nitrogen and by ensuring 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 e.g. 'Resin fire' what to consider when choosing a variety. Small-fruited cherry, panicle and bush tomato varieties are comparatively rarely affected.

Post-ripening tomatoes

How tomatoes turn red after all

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

  • You need a support for this, for example, a wooden board
  • Put board on the ground next to the plant in question
  • This is to prevent contact of the fruit with the soil
  • Then the plant bends over
  • Tomatoes should be on the board
  • Then put a mobile cold frame or cold box over the fruit
  • In the bed additionally cover with opaque fleece
  • Remove the cover once a day for ventilation
  • Fruits ripen within one to three weeks depending on weather conditions

Tip: Even if the appetite for ripe tomatoes in summer is great, you should never eat unripe, green tomatoes, because they are poisonous except for special green varieties. Solanine content in unripe fruit is so high that it is harmful to health.

Reduce the amount of watering

The deprivation of water can make the plants to advance the ripening of the fruits. However, it should not be started before the fall. As long as the plant grows and produces fruit, it depends on a regular and abundant supply of water.

In the fall, when the fruits have reached their final size and do not really want to turn red, extend the intervals between watering and water only about once every three days. Throttled watering 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

Similar to the deprivation of water is the deprivation of light. As long as the tomato plant grows and produces fruits and seeds, it cannot do without sufficient light. As soon as the fruits are fully grown, they can manage with much less light, because the light intensity hardly plays a role in the red coloration of the fruits. They can even turn red in complete darkness. To speed up the process, tomatoes in pots or tubs can now be placed in a shady place and plants in the bed can be covered with a plant fleece.

Pick 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 frost kills them, they should be harvested and allowed to ripen indoors. It is best to harvest them as soon as temperatures fall below 10 °C permanently.

  • Always harvest unripe tomatoes with stems
  • Without a stem, formation of cracks at the base of the stem is possible
  • Cracks are an entry point for germs
  • Mold often develops on the cracks, and the fruit spoils
  • Green tomatoes for post-ripening should not have any damaged spots
  • Check fruits for brown spots, risk of brown rot
  • Tomatoes can also ripen on the plant
  • To do this, cut off the entire plant
  • Tomato plants should be hung upside down in a warm place (18-20 °C)
  • Space with high humidity, for example, in a cellar
  • Light for post-ripening is not necessary
  • Typical red color will appear 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 lie on top of each other and should be regularly checked for damage or rot and the corresponding fruit should be sorted out. If you want, you can put an apple in the box and use the ripening gas for the ripening process.

Alternatively, the green, unripe fruits can be wrapped in newspaper, placed in a shoebox or simply in a bowl, covered and stored in a warm room until they turn red. Gradually, the fruits turn red and can be eaten. Taste nor aroma of the ripe fruit is usually not diminished by these measures.

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