Why tomatoes don’t turn red and ripe: 5 causes

Red, juicy tomatoes from our own garden taste like sun and freshness. But what to do if tomatoes don’t turn red and ripe? We name the five most common causes and give tips.

Wrong location

One of the most common reasons why the tomato does not ripen and turns red is improper location of the tomato plants. The fruits like it sunny and warm, in semi-shady locations the plants wither.

Did you know that tomatoes need at least 8 hours of sun a day? If the valuable sunlight is missing, a plant lamp in a greenhouse can help. These full-spectrum lamps equipped with LEDs help the fruit to ripen.

Another requirement for the optimal location for tomato plants is adequate wind and rain protection. In exposed places, the fruits do not turn red and ripe, despite prolonged exposure to the sun. Therefore, a greenhouse or the south side of the house are best suited as locations for tomato plants.

Wrong floor

Tomato is a demanding crop and only thrives in nutrient-rich, fresh soil. In a nutrient-poor soil, the tomato stays green for months and does not ripen. But over-fertilizing and supplying the wrong fertilizer can also slow down the ripening process or bring it to a standstill.

Optimal soil for tomato plants has the following characteristics:

  • Good drainage, no waterlogging
  • Rich in nutrients
  • Moderate proportion of clay
  • Neither too wet nor too dry
Note: A common mistake is an oversupply of nitrogen-rich fertilizers. Again, potassium or magnesium deficiency slows down the ripening process.

Too cold weather

Among the most common causes of fruit staying green for too long is an unfavorable, cold and rainy summer. If the location is wrong, the tomatoes will hardly ripen.

A plastic ripening hood or film can help to ensure that the fruit turns red and ripe outdoors. Under the tomato hood, the plants are not only protected from rain and wind, but are also in a warm, favorable environment. The tomato hood is especially recommended in unfavorable weather.

Tip: If fruits in the greenhouse remain unripe for a long time, place ripe bananas or apples near them. Both types of fruit are known to release high levels of the gaseous phytohormone ethylene or ethene during the ripening process. The plant hormone promotes the ripening of the fruit in the area.

If the weather is consistently unfavorable, tomato tubs and pots should be moved from the balcony or patio to a conservatory or indoors. The ripening process gets going in the warm air and on a sunny windowsill or in the light of a plant lamp.

Too much green

If tomatoes are still unripe at the end of the gardening season, the leaf mass may be too high. The fruit requires a lot of energy to ripen, but the leaves also use energy to grow and can also shade the fruit too much.

To harvest a juicy, bright red tomato with a full-bodied flavor, tomato plants need to be pinched regularly. Pruning means the removal of shoots that grow in the leaf axils. It is best to remove the side shoots promptly when they still measure a few centimeters. In this case, the shoots can be removed without pruning shears, just with your fingers.

Note: It would be a mistake to remove too many shoots. A tomato plant needs leaves for photosynthesis and healthy growth. Caution and a good sense of proportion are required when stinging.

Green or yellow collar disease

This unpleasant phenomenon is often observed in almost ripe tomatoes: around the stalk, the flesh is not red and soft, but greenish or yellow and hard. These parts of the fruit are inedible and should be cut off before consumption. Yellow or green collar disease is neither a contagious disease nor a parasite. Rather, it is a misdevelopment as a result of wrong treatment.

The causes of the phenomenon are:

  • Temperatures above 30 degrees Celsius
  • No shading due to a wrong choice of location or too intensive exhaustion
  • Lack of drainage, too clayey soil
  • Excessive watering
  • Supply of nitrogenous fertilizers
  • Lack of calcium, potassium and magnesium in the soil

frequently asked Questions

Yes, if the outdoor tomatoes are not turning red and ripe, you can transplant the outdoor tomatoes. Dig up the plant carefully so as not to damage the roots. Water the repotted plant copiously. Tomato plants in pots and containers easily tolerate a change of location.

Yes this is not a problem. Wrap the fruit in plain paper or a piece of cloth, place a ripe banana or apple nearby and wait a few days. Most fruits turn red and ripe. Alternatively, cut off the plant near the root and hang it up at home. Tomatoes only turn red and ripe in a warm and dry place.

Can I eat a green tomato? No, this is strongly discouraged. Unripe, green tomatoes contain around 30 milligrams of the natural toxin solanine per 100 grams of weight. After eating just two green tomatoes, symptoms such as headaches, nausea, cramps may appear. For comparison: red and ripe tomatoes contain only 1 milligram of solanine per 100 grams of pulp. 400 milligrams of this natural toxin can even be deadly.

Yes, “Green Zebra” is the most famous of such tomato varieties. Hardly any coloring forms in the fruit as it ripens, the tomato remains green but tastes full-bodied. You don’t have to worry about the solanine content – this dangerous active ingredient is broken down as “Green Zebra” ripens, just like classic red fruits ripen.

Kira Bellingham

I'm a homes writer and editor with more than 20 years' experience in publishing. I have worked across many titles, including Ideal Home and, of course, Homes & Gardens. My day job is as Chief Group Sub Editor across the homes and interiors titles in the group. This has given me broad experience in interiors advice on just about every subject. I'm obsessed with interiors and delighted to be part of the Homes & Gardens team.

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