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They come from the warm, sun-drenched regions of South and Central America. Due to their origin, tomatoes have not learned to defy the winter cold. Primarily in spring and autumn, ground frost can severely damage tomato plants and, in the worst case, destroy the hope of a rich harvest. You can find out why this is the case and what minimum temperature you need at night here. Use our tried-and-tested tips for the best precautions so that the delicious apples of paradise do not freeze to death.

temperature is important

Temperature is very important in tomato cultivation

Temperatures play a key role in the interaction of the growth factors of a tomato plant. All metabolic processes only run smoothly if the optimum temperature of 18 to 25 degrees Celsius is maintained, with an acceptable upper and lower tolerance.

The upper temperature limit of 45 degrees Celsius is not relevant for the subtropical nightshade plant in the Central European climate. Cold, on the other hand, poses a significant problem for the growth of tomato plants. While native perennials have been able to adapt to frost in the course of evolution, things get tricky for tomatoes well above freezing point.

temperature minimum

Minimum temperature defines the lower tolerance limit

In a combination of experience and scientific knowledge, a minimum temperature of 13 degrees Celsius has emerged for tomatoes. This limit must not be undershot even at night. If the mercury column falls below this limit, the plant reacts with the following thermomorphoses.

Here's how to do it:

  • curling of the leaves
  • Growth depression with shortened internodes (leaf spacing)
  • Leaves first turn reddish and then die
  • little to no flowering

Cold has a fatal effect on the pollen and its viability. At temperatures below 13 degrees Celsius, complete pollination no longer takes place. The result is only small, seedless fruits with hard flesh and a dull skin. On beefsteak tomatoes, the fruits then tear open from the top.

At temperatures below 10 degrees Celsius to below freezing, there is no fertilization at all, so that the affected flowers fall off in spring and there is a risk of a complete failure of the harvest. The reddish coloring of the leaves is due to a metabolic disorder as a result of frost, since the formation of sugar and starch comes to a standstill. As a result of the lack of energy, the entire plant dies if this cold phase lasts for a long time.

Protection against ground frost

Tips for protection against ground frost in spring

Tomato plants are planted in beds by mid to late May at the latest. For a later date, the summer vegetation phase is too short for ripe fruit to develop. Although the exodus of the Ice Saints by May 15 raises hopes that there will no longer be delayed ground frosts, the weather does not always adapt to the calendar. Until after the sheep cold in early/mid-June, there is still a risk of growth being impaired as a result of temperatures that are too low. With these precautions you can prevent the young tomato plants from freezing to death.

Here's how to do it:

  • If there is a risk of ground frost, cover the bed with garden fleece
  • ideally plant out under a polytunnel or a tomato house
  • Strengthen repeatedly with horsetail broth or liverwort extract during cultivation

Your paradise apples are better prepared for short-term cold stress between 1 and 12 degrees Celsius if you first harden off the young plants for 8 to 10 days in a partially shaded location on the balcony. If an unheated greenhouse is available for growing tomatoes, use a manure heater to keep the temperature above the minimum of 13 degrees Celsius.

To do this, dig the ground about 70 centimeters deep and fill the pit with horse manure or stable manure. Spread a 10 to 12 inch layer of compost over this to plant in. As the manure rots, a pleasant warmth is created that does not fall below the pain threshold of 13 degrees Celsius, even at night.

Save harvest after cold

This is how you save the harvest in the autumn cold snap

If the thermometer falls below 15 degrees Celsius at night in September, the last tomatoes that are still green will no longer ripen. Precautions that protected your tomato plants from cold stress in spring are in vain at the end of the season. However, the laboriously grown tomatoes do not have to fall victim to the frost, because they are among the climacteric fruits and therefore have the ability to ripen later.

Before the green apples of paradise freeze, proceed as follows:

  • Pick and wash an unripe tomato
  • Wrap in newspaper or black foil
  • air daily on a wooden shelf in a dark room at 18 to 20 degrees Celsius
  • alternatively, fill a box with dry peat and place the tomatoes inside, without letting them touch each other

If you place a fully ripe apple next to an unripe tomato, the ethylene gas emitted accelerates the ripening process. Instead of storing each fruit individually, you can uproot the entire plant and hang it upside down in the boiler room until the fruit is ripe. The leaves must not be removed, as they are still responsible for the care of the tomato plants.

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