Blossom end rot on a tomato is not a reason to abandon the entire harvest of a tomato plant. However, the plant gives you the signal to control the nutrient supply.

Table of Contents

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  1. the essentials in brief
  2. Identify blossom end rot
  3. causes and treatment
  4. Prevent blossom end rot
  5. Are tomatoes with blossom end rot edible?
  6. Other diseases caused by nutrient imbalance
  7. FAQ

    8. the essentials in brief

    • Blossom end rot can be recognized by dark, watery spots on the blossom base of the fruit.
    • In contrast to late blight and late blight, blossom end rot is due to an undersupply of calcium.
    • Proper fertilization and a neutral soil pH can restore the imbalance.
    • Proper water management ensures constant nutrient transport and prevents blossom end rot.

    Identify blossom end rot

    The earlier blossom end rot is discovered, the more likely it is that the tomato plant will make a full recovery. That is why tomatoes are regularly checked for dark rotten spots (necrosis), whether in a bucket, in a bed or in a greenhouse. The initial stage of blossom end rot is revealed as a brown, watery indentation at the lower tip of the fruit, i.e. at the former base of the blossom.

    What is blossom end rot?

    Blossom end rot is not caused by bacteria or fungi, but is only due to an undersupply 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 sufficient water. The cause of an undersupply is, on the one hand, the wrong balance of nutrients. On the other hand, calcium does not reach the tomatoes if there is no water transport due to prolonged drought. Because only when leaves and fruits evaporate water do the roots draw in liquid and the mineral dissolved in it.

    appearance and symptoms

    Blossom end rot is noticeable in the early stages of calcium deficiency by small, dark spots on what used to be the beginnings of the blossoms. Without countermeasures, these become larger over time, watery or glassy and can take up the entire lower half of the tomato. Starting at the base of the blossom, the fruit curves in and gradually becomes leathery, hard and black. Under certain circumstances, young leaves also show stunted growth and appear slightly yellowish.

    Large and elongated tomato varieties such as plum tomatoes are particularly affected. Blossom end rot typically occurs in summer from June to August. The bottom fruits are often the first to suffer from the undersupply and rarely all the tomatoes on a truss at the same time. As soon as the tomato has rotted on one side, it falls off the bush by itself.

    Blossom end rot or late blight?

    caption: A comparison of blossom end rot and late blight

    Left: blossom end rot, Right: brown rot

    In contrast to late blight and late blight, blossom end rot is not a disease but represents a calcium deficiency. On the other hand, late blight is caused by the harmful fungus "Phytophthora infestans". This gets into the plant via rainwater or splashing water when watering incorrectly. Unlike blossom end rot, late blight is contagious and affects nearby potatoes, among other tomato plants.

    It is worth emphasizing the clear differences that allow the exact determination of the rot. The disease caused by the fungus starts with the (lower) leaves first. Brown spots appear on these, which have a blurred edge to the leaf green and die off after a while. The same clinical picture is then also seen in the fruit, whereby the necrotic areas can start anywhere on the tomato and - unlike blossom end rot - does not necessarily have to start at the lower end of the fruit.

    causes and treatment

    Blossom end rot always has its origins in an undersupply of the important plant nutrient calcium. However, there are several reasons why the tomato cannot absorb enough calcium. Before countermeasures can be initiated, the causes of the undersupply must first be determined.

    Incorrect fertilization

    As a rule, there is sufficient calcium in the soil to which compost has been added, for example. However, if the proportion of nitrogen is also increased with a fertilizer such as blue grain, the plant will grow faster. Often even too quickly, so that many new leaves and shoots appear in a very short time, which have priority in the plant's own supply of nutrients - the tomato consequently 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 uptake of calcium by the roots. Such an imbalance often arises when explicit nutrients have been administered with inorganic fertilizers. A calcium fertilizer can be used sporadically to restore the correct balance. From a long-term perspective, however, organic fertilization from compost, plant manure or stable manure is recommended, as they may have fewer nutrients overall, but they are suitably balanced.

    Incorrect soil pH

    An imbalance of minerals is inevitably reflected in the ampH value: if there is a lack of calcium, the soil is usually acidic (>6). By adding lime, the soil can be brought back into a neutral pH range of around 7. For this purpose, the primary rock flour from Cuxin is added to the soil in a proportion of 200 - 300 g/m². Since the natural flour costs only 12 euros in a 10 kg bucket, such liming is not only ecological, but also inexpensive.

    our recommendation
    Cuxin Rock Powder Bucket 10KG
    9.33 EUR To the product
    medium definition application
    algae lime Deposits of red algae, contains calcium carbonate, magnesium carbonate and silicic acid Work algae lime lightly into the soil around the tomato, water vigorously
    Calcium effervescent tablets Buy calcium effervescent tablets in tubes from the drugstore Crumble the tablets and gently work them into the soil around the tomato, or simply insert the entire tablet into the soil in the root area and water vigorously
    calcium carbonate pure garden lime (9.70€) (9.70EUR) contains natural calcium carbonate Work garden lime lightly into the soil around the tomato, water vigorously
    eggshells Chicken egg shells Crush two or three egg shells, let stand in a liter of water for two to three days and pour the tomato with it
    rock flour natural calcium carbonate along with other minerals and trace elements Work rock flour (14.13€) (12.33EUR) (basic rock flour) into the soil around the tomato and pour vigorously

    Calcium for tomatoes

    Originally, the mineral comes from weathered rock such as basalt. In order for it to be absorbed by living beings, it must be dissolved in water, for example. One way to supply tomato plants with calcium is with effervescent tablets like those from Hexal. They consist only of the mineral and 100 pieces cost around 25 euros. They can simply be worked into the potting soil in a crumbled form. Then water well so that the roots can absorb the calcium.

    our recommendation
    CALCIUM 1000 HEXAL effervescent tablets 100 pcs
    22.36 EUR To the product

    blossom end rot and baking soda

    Baking powder has a fungicidal effect and can therefore be used against late blight and late blight. However, the cause of blossom end rot is a calcium deficiency. So baking soda has no direct effect on blossom end rot. The home remedy can at most increase the pH value in the soil, which can benefit calcium absorption.

    Prevent blossom end rot

    Aside from fertilizing, getting the right balance around the water is crucial to protecting the tomato from blossom end rot. The right watering, the weather and the relative humidity are particularly important. If the parameters are correct in these areas, sufficient calcium can be transported into the fruit.

    Proper casting

    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 fruit. Therefore, proper watering is the most important step in preventing blossom end rot. The following proven tools also have the advantage that they avoid splashing water on the leaves. This also avoids the risk of fungal infestation.

    caption: Tools for watering tomatoes

    There are several ways to water tomatoes without splashing water

    plant pot. An ordinary clay pot with a hole in the bottom is planted in the ground near the tomato plant. Future watering is done exclusively over the clay pot. The tomato roots will grow in the direction that the water comes out of the pot when you water it.

    casting ring. In principle, the casting ring works like the usual plant pot with a hole. However, the tool, which costs around 10-20 euros, has the advantage that predators such as snails are kept away from the plant. Because between them is a pool of water that is difficult to overcome.

    Olla. The special thing about the watering aid is its size: from a capacity of 1 L to an impressive 6.5 L. The larger the capacity, the more plants can be supplied with water over a longer period of time. The watering ball is available in a price range of around 30 to 50 euros.

    weather

    In changeable summer months, the frequency of blossom end rot increases. The sensitive tomato hardly tolerates particularly strong temperature fluctuations. If the soil then dries out during a sudden heat wave, it can become critical for the plant. This can be remedied by a greenhouse, in which there is usually a more stable climate and the plant is protected from external influences.

    humidity

    Despite the weather, tomatoes in greenhouses often suffer from blossom end rot. This can usually be attributed to excessive humidity. The water and nutrient transport in the plant is driven by evaporation and the associated drawing of water. However, if the air is already saturated with water, the natural transpiration of the leaves is restricted. Greenhouses should therefore be ventilated regularly so that the relative humidity is between 60-70%.

    In addition, plants should be planted far enough apart to give the leaves enough space to "sweat". This applies to both the greenhouse and the bed. Pinching out, i.e. removing axillary shoots, also ensures more space and circulation between the leaves.

    Are tomatoes with blossom end rot edible?

    Opinions differ on whether tomatoes with blossom end rot are still edible. Some argue that the rot only came about because of an undersupply and not because of bacteria or fungi. Therefore they are edible. Other experts counter that pathogens enter through the rotten spots and contaminate the entire tomato, eventually rendering it inedible. However, it is clear that the affected tomatoes cannot be stored.

    Other diseases caused by nutrient imbalance

    In addition to blossom end rot, there are other diseases that can result 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.

    caption: Deficiency symptoms in tomato plants

    Signs of a deficiency or excess of nutrients can be seen in different parts of the plant

    nitrogen deficiency. A lack of nitrogen occurs when fertilizers are rarely used. The older leaves turn yellow, then brown, and fall off. The growth is stunted and the overall leaf color is rather pale green. The yellowing will spread to the top and younger leaves if the deficiency is not remedied.

    Potassium deficiency/green collar. The so-called green collar is easy to recognize on the tomato fruits. If there is a potassium deficiency at the base of the stem, these remain green. In addition, if there is an insufficient supply of potassium, the leaves will turn brown and dry starting from the leaf edge. Similar to blossom end rot, too much nitrogen is a common cause of deficiency.

    magnesium deficiency. If the tomato grows on sandy and acidic soils, it sometimes suffers from a lack of magnesium. This is shown by whitish-brown spots on the leaves, which eventually take up the whole leaf. Only the leaf veins continue to shimmer green through the fabric. An inorganic fertilizer covers the need here.

    Overfeeding/spoon leaf drought. A common phenomenon is the already mentioned over-fertilization with nitrogen. This imbalance is best recognized by the rapid growth of the plant, with the new shoots and leaves feeling soft and curling up. To counteract this, it is 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, starting at the leaf tip. Furthermore, new leaves tend to become small and hard. Leaf edges may occasionally die off. The best way to deal with the 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, immature tomatoes affected by 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, which develop into watery rotten 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 a bacterial or fungal disease, it can easily end up in the compost. Plant parts that are infected with late blight or brown blight should not be composted.

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Vegetable garden