Blossom end rot on a tomato is not a reason to abandon the entire crop of a tomato plant. However, the plant is giving you the signal to check the nutrient supply.
How to identify and prevent blossom end rot on tomatoes?
Blossom end rot on tomatoes is caused by a calcium deficiency and appears as brown, watery spots on the underside of the fruit. To combat it, a regulated water balance should be maintained and infected tomatoes should be removed. Prevention includes proper watering, attention to weather conditions, and adjustment of humidity.
How is blossom rot recognized and combated?
Blossom end rot occurs due to calcium deficiency, which is promoted by dry periods and insufficient water supply. During these periods there is enough calcium in the soil, but the tomato plant cannot absorb the nutrient. Brown spots on the underside of the tomato fruit are an identifying feature. The deficiency can be combated by maintaining a regulated water balance and removing infected tomatoes.
Identifying blossom end rot
The sooner blossom end rot is discovered, the more likely the tomato plant is to fully recover. That's why tomatoes - whether in the bucket, in the bed or in the greenhouse - are regularly checked fordark rotten spots(necrosis). The initial stage of blossom end rot appears at the lower tip of the fruit, i.e.at the former flower base, as a brown, watery indentation.
What is blossom end rot?
The cause of blossom end rot is not bacterial or fungal, but is only due to aundersupply of the plant nutrient calcium. The mineral creates stable cell walls in the leaves and fruits. If there is a lack of this important nutrient, the cell walls collapse and the tissue underneath dies and turns dark.
Ideally, calcium is present in the soil in the optimal mixing ratio with other minerals and can be absorbed by the roots with enough water. The cause of an undersupply is, on the one hand, the incorrect balance of nutrients. On the other hand, calcium does not reach the tomatoes if there is no water transport due to persistent drought. Only when leaves and fruits evaporate water does the root draw in liquid and the mineral dissolved in it.
Appearance and symptoms
Blossom end rot becomes noticeable in the early stages of calcium deficiency throughsmall, dark spots on the former flower bases. Without counteraction, these become larger, watery or glassy over time and can take up the entirelower half of the tomato. The fruit bulges from the base of the flower and gradually becomes leathery, hard and black. Under certain circumstances, young leaves may also have stunted growth and appear slightly yellowish. Find out about black spots on tomatoes.
Large and elongated tomato varieties such as bottle tomatoes are particularly affected. Blossom end rot typically occurs in the summer from June to August. Often the lowest fruits suffer first from a lack of supply and rarely all tomatoes on one vine at the same time. As soon as one side of the tomato has rotted, it falls off the bush on its own.
Blossom end rot or late blight?
Left: blossom end rot, right: brown rot
Unlike late blight, blossom end rot is not a disease, but represents a calcium deficiency. Late blight, on the other hand, is caused by the harmful fungus “Phytophtora infestans”. This gets into the plant via rainwater or splash water when watering incorrectly. Unlike blossom end rot, late blight is contagious and affects other tomato plants as well as potatoes growing nearby.
The clear differences that enable the precise determination of the rot should be emphasized. The disease caused by the fungus begins first on the (lower) leaves. Brown spots appear on these, which have a blurred edge to the green leaf and die off after a while. The same clinical picture can then also be seen in the fruits, whereby the necrotic areas can start anywhere on the tomato and - unlike blossom end rot - do not necessarily have to start at the lower end of the fruit.
Causes and control
Blossom end rot always has its origins in aUndersupply of the plant nutrient calcium However, there are several reasons why the tomato cannot attract enough calcium. Before countermeasures can be initiated, the causes of the undersupply must first be determined.
Incorrect fertilization
As a rule, there is enough calcium in the soil that has been mixed with compost, for example. However, if the proportion of nitrogen is also increased significantly with a fertilizer such as Blaukorn, the plant grows faster. Often too quickly, so that many new leaves and shoots appear in a very short time, which are given priority in the plant's own supply of nutrients - the tomato therefore receives less calcium. Then nitrogen fertilization should be suspended at least once.
In large quantities, the minerals magnesium, potassium, ammonium and sodium also directly inhibit the absorption of calcium via the roots. An imbalance often arises when explicit nutrients have been administered with inorganic fertilizers. To restore the correct balance, a calcium fertilizer can be used sporadically. From a long-term perspective, however, organic fertilization from compost, plant manure or manure is recommended, as they contain fewer nutrients overall, but they are appropriately balanced.
Incorrect soil pH
An imbalance of minerals is inevitably reflected in the pH value: If there is a lack of calcium, the soil is usually acidic (>6). By adding lime, the soil can be brought back to a neutral pH range of around 7. To do this, Cuxin's primary rock flour (€15.00 at Amazon) is added to the soil in a ratio of 200 - 300 g/m². Since the natural flour only costs 12 euros in a 10 kg bucket, such liming is not only ecological but also inexpensive.
Calcium for tomatoes
The mineral originally comes from weathered rock such as bas alt. In order for it to be absorbed by living creatures, it must be dissolved in water, for example. One way to supply tomato plants with calcium is with effervescent tablets. Another option is to use a ready-made mixture of calcium, manganese and zinc, which prevents blossom end rot and contributes to better coloring of the fruit. Watering is carried out as a preventive measure and the plant is sprayed if rot has already occurred.
Tip
If the heat is too high, the absorption of calcium via the roots is disrupted. In this situation we recommend spraying the leaves.
Overview: Remedies against blossom end rot
| Medium | Definition | Application |
|---|---|---|
| Algae limestone | Deposits of red algae, contains calcium carbonate, magnesium carbonate and silica | Work the seaweed lime lightly into the soil around the tomato, water vigorously |
| Calcium effervescent tablets | Buy calcium effervescent tablets in a tube from the drugstore | Crumble the tablets and lightly work them into the soil around the tomato or simply insert the whole tablet into the soil in the root area and water vigorously |
| Calcium liquid fertilizer | Mixture of calcium, manganese and zinc | Spray the plant or mix with irrigation water |
| Calcium carbonate | pure garden lime, contains natural calcium carbonate | Work garden lime lightly into the soil around the tomato, water vigorously |
| Eggshells | Shells of chicken eggs | Crush two to three eggshells, let them stand in a liter of water for two to three days and water the tomatoes with them |
| Rock flour | natural calcium carbonate along with other minerals and trace elements | Work rock powder (primary rock powder) into the soil around the tomato and water vigorously |
Does baking soda help against blossom end rot?
Baking soda has a fungicidal effect and can therefore be used against late blight and brown rot. However, the cause of blossom end rot is a calcium deficiency. So baking soda hasno direct effect on blossom end rot. The most the home remedy can do is increase the pH value in the soil, which can benefit calcium absorption.
Preventing blossom end rot
Aside from fertilizing, the right amount of water is crucial to protecting the tomato from blossom end rot. Correct watering, the weather and the relative humidity are particularly important. If the parameters in these areas are correct, sufficient calcium can be transported into the fruit.
Proper watering
The regular supply of water keeps the continuous transport of nutrients in the plant going. If there are frequent dry periods, calcium can no longer be sufficiently transported to the fruits. That's why proper watering is the most important step in preventing blossom end rot. The following tried and tested tools also have the advantage of avoiding splashing water on the leaves. This way you avoid the risk of fungal infestation.
Claypot: An ordinary clay pot with a hole in the bottom is inserted into the soil near the tomato plant. Future watering will be done exclusively via the clay pot. The tomato roots grow in the direction where the water comes out of the pot when watering.
Watering ring: The watering ring basically works like the usual plant pot with a hole. However, the aid has the advantage that predators such as snails are kept away from the plant. Because there is a pool of water between them that is difficult to overcome.
Olla: The special thing about the irrigation aid is its size: from 1 L capacity to an impressive 6.5 L. The larger the capacity, the more plants can be watered over one be supplied for a longer period of time.
Weather
In changeable summer months, the frequency of blossom end rot increases. The sensitive tomato can hardly tolerate particularly strong temperature fluctuations. If the soil dries out during a sudden heat wave, things can become critical for the plant. A greenhouse can help, as the climate is usually more stable and the plant is protected from external influences.
Humidity
Tomatoes in greenhouses still often suffer from blossom end rot, despite the weather. This can usually be attributed to excessive humidity. The transport of water and nutrients in the plant is driven by evaporation and the associated retention of water. However, if the air is already saturated with water, the natural transpiration of the leaves is restricted. Therefore, greenhouses should be ventilated regularly so that the relative humidity is between 60-70%.
In addition, plants should be planted with enough distance between them so that the leaves have enough space to “sweat”. This applies to both the greenhouse and the bed. Pinching, i.e. removing axillary shoots, also ensures more space and circulation between the leaves.
Are tomatoes with blossom end rot edible?
Opinions differ on the question of whether tomatoes with blossom end rot are still edible. Some argue that the rot only occurred due to a lack of supply and not because of bacteria or fungi. That's why they are edible. Other experts counter that pathogens enter through the rotten areas and contaminate the entire tomato, ultimately making it inedible. However, it is clear that the infected tomatoes cannot be stored.
Other diseases caused by nutrient imbalance
In addition to blossom end rot, there are other diseases that can arise from an imbalance of minerals in the soil. Most often this circumstance is due to improper fertilization. A deficiency can be compensated for in the short term with inorganic mineral fertilizers or in the long term with plant manure and compost.
Nitrogen deficiency: A deficiency of nitrogen occurs when fertilization is generally infrequent. The older leaves turn yellow, then brown and fall off. The growth is stunted and the overall leaf color is rather pale green. Yellowing will spread to the upper and younger leaves if the deficiency is not corrected.
Potassium deficiency/green collar: The so-called green collar can be easily recognized on the tomato fruits. If there is a potassium deficiency, these remain green at the base of the stem. In addition, if there is a lack of potassium, the leaves will turn brown and dry starting from the edge of the leaf. Similar to blossom end rot, too much nitrogen is often the reason for a deficiency.
Magnesium deficiency: If the tomato grows in sandy and acidic soils, it sometimes suffers from a magnesium deficiency. This is shown by whitish-brown spots on the leaves, which eventually cover the entire leaf. Only the leaf veins continue to shimmer green through the tissue. An inorganic fertilizer covers the need here.
Overfertilization/Spoonleaf: A common phenomenon is the already mentioned overfertilization with nitrogen. This imbalance is best recognized by the rapid growth of the plant, with the new shoots and leaves feeling soft and curling. To combat this, it's best to wait and not fertilize.
Phosphorus deficiency: The most noticeable symptom of a phosphorus deficiency is the reddish-purple to black discoloration of the leaves, which begins at the tip of the leaf. Furthermore, new leaves tend to be small and hard. Leaf edges may occasionally die off. The best way to combat phosphorus deficiency is to add organic matter such as compost.
FAQ
Should tomatoes with blossom end rot be removed from the plant?
Even if it hurts, unripe tomatoes infected with blossom end rot should also be removed from the vine. The fewer fruits the plant has to supply with calcium, the fewer deficiency symptoms occur overall.
Which plants can get blossom end rot?
In addition to tomatoes, zucchini and peppers can also suffer from blossom end rot. The appearance is the same for all three: small black dots at the base of the flowers that develop into watery rot spots.
Can the parts of the tomato plant with blossom end rot go into the compost?
Since the tomato affected by blossom end rot does not have any bacterial or fungal disease, it can easily end up in the compost. However, plant parts that are infected with late blight or brown rot should not be composted.