Tomato plants are extremely sensitive to cold, which is why, in principle, they should be used only after the Ice Saints and harvested in the fall at the latest. Nevertheless, it can always happen that cold nights or sub-zero temperatures arrive unexpectedly. Damage to the plants is usually unavoidable in such situations, but in many cases the plants can still be saved.
What are the effects of frost?
We talk about frost when the temperature drops below zero degrees for a while. An indicator of frost is the formation of hoarfrost, here ice crystals form on the plants. Due to the low temperatures, the cells in the plant freeze and burst open as soon as it gets warmer. Likewise, it often happens that the water in the soil freezes. As a result, the plants are no longer able to absorb water and die of thirst.
In addition, the following problems can occur:
- the formation of flowers is affected
- as well as the viability of pollen
- the fruits become hard
- and have a dull skin
- unfertilized tomatoes may crack and scar
General signs of frost damage
In most cases, older tomato plants, as well as new shoots, are especially susceptible to late frost. As a rule of thumb, if the lower part of the plant is frostbitten, it usually needs to be discarded. However, if only the upper part of the plant is affected, it is wounded but may survive.
Often, frost damage can be identified by these characteristics:
- discolored foliage
- curling leaves, which may fall off
- drooping shoots
- soft stems
- soft, mushy fruits
- in spring the plant does not sprout again
Additionally, you can tell if the plant is frostbitten by gently scraping the bark off with your fingernail. If the shoot underneath is green, then the plant is still alive. If, on the other hand, the shoot is discolored brown, then this is often an indication that the plant is already dead. In this case, the plant can no longer be saved and must be disposed of.
Different types of cold damage
Basically, a distinction is made between cold damage and frost damage. These differ on the one hand from the outgoing temperature and on the other hand from their effects.
Cold damage / cold stress
Cold nights are often the trigger for cold damage: This is because the risk of temperatures dropping too much is particularly increased at night. However, cold nights are not the only danger to tomato plants. Because if the temperature is below 10 °C for more than 14 days, the tomato plants can also be damaged. If the temperature drops below 5 °C, cold damage occurs after only 6-8 days.
Cold damage can be recognized by these characteristics:
- lightening between the leaf veins
- irregular color development of tomatoes
- premature softening
In the case of cold damage, the tissues are weakened, which in turn leads to cellular dysfunction. Plant growth is disrupted, root development is prevented, and pollination is impaired. If daytime temperatures are around 15 degrees, as well as nighttime temperatures around 10 degrees, this can lead to malformed or even absent fruit.
Frost injury occurs when the temperature drops below 0 degrees. The subzero temperatures can damage only part of the plant, but can also damage the entire plant. Frost damage is caused by ice forming on the plant. If the frozen parts of the plant thaw too quickly, the tissue is damaged as the cells burst open.
The symptoms of frost damage are manifested as follows:
- the foliage turns brown
- the leaves dry up and die
- excessive softening
- withered appearance
- shoots are brown inside
- plant dies
Saving potted plants
Saving potted plants is usually less complicated and more successful than saving outdoor tomatoes. If, for example, balcony tomatoes have been exposed to sub-zero temperatures, they should be brought indoors.
Then proceed as follows:
- Water the plant with warm water
- Ideally, put a glass container over the plant.
- this will create a kind of mini greenhouse effect
- Place the plant on a sunny windowsill
If the potted plant can not be moved indoors, it is worth trying to protect it from the cold afterwards. After all, tomato plants can often survive despite damage suffered from the cold. For individual plants, it is advisable to use a tomato cover or a fleece.
Saving plants in the vegetable bed
If outdoor tomatoes have suffered cold damage, this can often be seen in the dead shoots. Although these represent unnecessary ballast for the tomato plants, they should not be removed immediately.
It is better to proceed as follows:
- wait until the plant sprouts new shoots.
- this will make it easier to identify dead shoots
- cut them off carefully
- disinfect the cutting tool beforehand
- because open wounds are caused by cutting
- and the plant is weakened due to the cold damage
- this increases the risk of disease and pest infestation
- then water the plants
- so that they do not warm up too quickly due to the sun.
Especially for outdoor tomatoes it is recommended to provide protection against the cold. For this purpose, the installation of a foil tunnel has proven to be particularly effective. Individual plants can be protected – like potted plants – with a tomato cover or a fleece.
What to do with frozen tomatoes?
If the tomato plants have suffered frost damage, it is advisable to harvest all ripe as well as almost ripe tomatoes. Green fruits, which have reached their full size, can also be harvested, as they are suitable for post-ripening. Tomatoes that have suffered from cold damage are suitable for consumption, but their taste cannot compete with “healthy” tomatoes.
Which is why the following use is advisable:
- use fruits 1 to 2 days after harvesting
- remove the damaged parts from the tomatoes
- they can be eaten
- but it is better to process them
- for example in stews, sauces or soups