Yellow leaves on rhododendrons indicate an iron deficiency. Azaleas often suffer from the so-called chlorosis due to an incorrect pH value.
Rhododendrons, which belong to the ericaceous plants, are particularly susceptible to chlorosis. In the case of chlorosis on rhododendrons, there is often an indirect iron deficiency. As a result, not enough of the green pigment chlorophyll can be produced. But without the dye, photosynthesis is no longer possible. Next to the unsightly leaves, this is the main reason why chlorosis should be treated.
Detect chlorosis
The symptoms of chlorosis are very easy to recognize, especially with rhododendrons. If the leaves turn yellow, with the leaf veins often remaining green, chlorosis is present. As mentioned above, an iron deficiency is responsible for this, which is actually none at all. Because most soils contain enough iron, but above a certain pH value, rhododendrons find it very difficult to absorb it.
Prevention of yellow leaves on rhododendrons and azaleas
Heather plants depend on a relatively low pH value of 4.5 to a maximum of 6. Otherwise the plants are no longer able to absorb enough iron and iron deficiency chlorosis occurs. To ensure a sufficient supply of iron, the pH value in the soil should be measured before each planting. Many companies offer special test sets for this. If the pH value is 6 or higher, generous amounts of rhododendron earth should be incorporated before planting. If you have a calcareous location and don't want to do a lot of digging, then try the INKARHO varieties. There the plants are grafted with rootstocks that can also cope with higher pH values.
Chlorosis and chlorosis: treating and fighting
If there is severe chlorosis, foliar fertilization should be carried out. As a result, the leaves are supplied with iron again for a short time. If possible, only foliar fertilizers should be used, since normal fertilizers are too concentrated and can lead to leaf burns. In addition to foliar fertilization, you can also fertilize normallybe, but then iron should be fertilized in chelate form. The chelate combined with the iron is much better absorbed by the rhododendron. In both cases, however, you will only get rid of the chlorosis for a short time. If the pH value in the soil is too low, you will always have problems with chlorosis on your rhododendrons.
Tip: If the reason for the iron deficiency is not the pH value of the soil but the actual amount of available iron, you can use an iron-rich organic fertilizer such as our Plantura Apply organic hydrangea fertilizer.