Yellow leaves on hydrangeas: how to detect an iron deficiency
Yellow leaves on hydrangeas can indicate an iron deficiency. We will show you how to recognise and successfully combat chlorosis.
If the leaves of your hydrangeas (Hydrangea) turn yellow, the cause can be an iron deficiency, also known as chlorosis. This type of chlorosis is unfortunately common in hydrangeas. The cause is usually a lack of nutrients. This deficiency leads to yellowing between the leaf veins. The green pigment is needed for photosynthesis and chlorophyll production and is essential for the survival of every plant. Therefore, it is crucial to eliminate the yellowing on the leaves as soon as possible.
Yellow leaves on hydrangeas: chlorosis
In the following, we discuss if yellow leaves on hydrangea are a symptom of chlorosis. In addition to information on how to combat an iron deficiency successfully, you will also find tips on how to prevent chlorosis in hydrangeas.
Recognising chlorosis in hydrangeas
Chlorosis-stricken hydrangeas share the same symptoms, regardless if they are planted in a tub or a garden bed. The young leaves turn yellow at first, while the thick leaf veins often remain green. If the chlorosis is untreated, it can quickly spread.
Preventing chlorosis in hydrangeas
The missing nutrient in hydrangeas is almost exclusively iron, although there is almost always enough of it in the natural soil. The reason for the deficiency is therefore not a lack of iron in the soil, but that the hydrangea cannot absorb the iron present in the soil. This occurs when the pH value is too high. The hydrangea thrives best in low pH values of the soil at around 4 – 5.5. We would like to point out that the different colours of the hydrangea flower also depend on the pH value. For example, the blue hydrangea needs a pH value of 4 – 4.5 in order to absorb enough aluminium for the blue flower.
To determine the correct pH value of the soil, use a pH test which is available in garden centres or online. If the measured pH value is too high, it can be lowered with rhododendron substrate, lime-free peat or Epsom salt. It is recommended to plant the potted hydrangeas in rhododendron soil. Then, you won’t have to worry about chlorosis.
Successfully combating chlorosis on hydrangeas
An actual iron deficiency occurs quite rarely in hydrangeas. It is more likely to affect potted plants than those planted out in the garden bed. If the measured pH value of the soil is according to hydrangea preferences, but the leaves are still yellow, fertilise the plant. This can be done once through leaves or normally through the soil. It is important to pay attention to the correct nutrient concentration when fertilising by the leaves. If there are too many nutrients, the leaves can suffer burns. A standard fertiliser that is absorbed through the roots of the plant can do just as well.
If you would like to learn more about different hydrangea varieties, visit our article here.