Yellow leaves on plants indicate an iron deficiency. Hydrangeas, roses and rhododendrons are particularly susceptible to chlorosis.
Chlorose, also known as bleach, is a common phenomenon in plants such as azaleas and hydrangeas. But what actually happens with this disease? Basically, chlorosis is a lack of the green pigment chlorophyll. However, this dye is essential for the survival of every plant, as it captures the energy of the sun's rays. Therefore, chlorosis should always be treated. The causes of the disease could hardly be more diverse. However, in our region there are often the same triggers for leaf disease. Here you can find out why some plants can be more severely affected by chlorosis and how you can get the problem under control in the short and long term.
Detect chlorosis
Detecting chlorosis is easy! If a leaf contains too little of the green pigment chlorophyll, it will appear yellow or even partially red in autumn. However, chlorosis is not always a bad sign. Perennial plants break down their chlorophyll in the fall and store the nutrients thus recovered for the next season. Even with annual plants, chlorosis does not necessarily have to be bad. Old leaves in particular, which are shaded by many new leaves, are unnecessary ballast for a plant. The chlorophyll in these leaves is also broken down and the leaves turn yellow and eventually fall off. However, if the yellowing of the leaves is rampant or new leaves are affected, then it is a harmful chlorosis. If the cause is not combated, the yellow leaves can die off after a while. In our soils, the cause is often an iron deficiency, but a nitrogen deficiency often leads to the dreaded chlorosis. If one of these two nutrients is missing, chlorophyll can no longer be produced. Of course, chlorosis can also occur if other nutrients such as boron or magnesium are missing, but such a case occurs only very rarely.
Chlorose species
Unfortunately, chlorosis is not the same as chlorosis. There are different forms of leaf disease, such as peak chlorosis or area chlorosis. Despite the different types of chlorosis, it is difficult, even for experts, to identify the cause with certainty. For this reason, we limit ourselves to leaf yellowing, which is easy to distinguish. If chlorosis occurs first in the younger leaves, then iron is usually missing. However, if the old leaves turn yellow first, this is a sure sign of nitrogen deficiency. In rare cases, the chlorosis occurs in a mosaic on the leaves. Then it is almost certainly a virus that has infected the plant. Unfortunately, only resistant varieties help against plant viruses. Direct combat is not possible. As you may have noticed from reading the text, the most common reason for chlorosis is a nutrient deficiency. However, so-called bad weather chlorosis can also occur. This is because certain weather conditions impede the uptake of nutrients by the roots. Prolonged drought can lead to leaf chlorosis, since the roots cannot absorb nutrients such as magnesium and nitrogen without water. However, continuous waterlogging and cold ground is just as bad. Especially with the nutrient iron, dripping wet roots lead to reduced iron absorption and thus to chlorosis. This is especially true for wine.
Prevent chlorosis and iron deficiency
Since the reason for chlorosis in Germany is often iron deficiency, we devote special attention to this topic. Incidentally, in very few cases is there a real iron deficiency. Rather, certain circumstances mean that plants cannot absorb the iron that is present. The pH value in the soil has the greatest influence here. If the value rises above 6.5, less and less iron is absorbed by the plant. PH values below 6, on the other hand, promote iron absorption and must therefore be aimed at in the case of chlorosis. For this reason, if you have chlorosis, you should first measure the pH of the soil. If the suspicion that the soil is too alkaline is confirmed, Epsom s alt or peat will help. When using Epsom s alt, it is essential to comply with the manufacturer's specified quantities and if peat is used, it must be lime-free. However, it is not the case that all plants are at a pH above6.5 suffer from chlorosis. This is because plants have to become active themselves in order to absorb iron. They release organic acids through the roots and thereby absorb more iron. Some plants like citrus and rhododendron just aren't as good at it as other plants. Incidentally, even varieties of a plant species can differ greatly in terms of iron absorption. If you have major problems with chlorosis, other preventive and long-term measures can be taken in addition to changing the pH value:
- Regular watering in dry weather (make sure to moisten the entire root ball)
- Lime impairs iron absorption (very calcareous tap water is also bad)
- In case of waterlogging, work compost into the soil, this will better supply the roots with air
- Iron deficiency is more likely to occur in store-bought substrates, natural soil is usually rich in iron
Chlorosis and chlorosis: treating and fighting
Fighting chlorosis is not that difficult. If you have already ruled out that the pH value is to blame for the chlorosis, there may actually be an iron deficiency. This often happens when growing tomatoes and roses in pots. It is rather irrelevant which nutrient is really responsible for the chlorosis. Because most of the time, the lack of nutrients is compensated with a fertilizer that contains all the important nutrients. When choosing a fertilizer, however, you should not just go by the price. Cheap supermarket fertilizer usually only contains the most important nutrients such as nitrogen, phosphate and potassium. Make sure that the fertilizer also contains all the so-called micronutrients, including: iron, manganese, copper, zinc, boron and molybdenum. In addition to the essential trace elements, a good fertilizer also contains a very specific form of iron, the chelate. A chelate envelops the iron molecules in the soil, allowing the plants to absorb the iron much better. Incidentally, this mechanism was taken from nature. Sweet grasses such as wheat, corn and rice can themselves form so-called chelators in their roots. As a result, these plants often have fewer problems with iron deficiency. A particularly quick solution to getting chlorosis under control is foliar fertilization. Foliar fertilization absorbs the nutrients directly and can be used. But beware: When foliar fertilization, iron with chelate must not be used, as it can damage the leavescan damage. Therefore, it is better to use special foliar fertilizers. Please do not despair if the already yellow leaves fall off or die. Unfortunately, chlorosis cannot always be reversed. But as long as the new leaves are lush green, everything is literally green.
The following products have proven themselves in our garden:
- Rose fertiliser: High-quality special slow-release fertiliser, which supports the leafy green with 2% magnesium oxide and iron.
- Tomato fertiliser: high-quality special slow-release fertiliser, which ensures tasty, he althy fruit and a rich harvest.
You can find out how to specifically identify and treat chlorosis on geraniums in our special article.