Rhododendron gets yellow leaves / brown spots

Rhododendrons are among the most popular garden plants in Germany. Caring for them is easy if the location meets the needs of the rhododendron. Of the rhododendron needs a loose, well drained, acidic soil. The bushes do not tolerate lime at all. If the soil is too calcareous or the pH value of the soil is too high, deficiency symptoms appear in the plant in the form of yellow leaves. If there is a pest infestation and too much sunlight, the leaves develop brown spots. Quick help is required so that the plant can recover.

Diseases

If the leaves of the rhododendron turn pale yellow, it is suffering from chlorosis, also known as calcium chlorosis. The disease is a typical symptom of deficiency when the soil is too calcareous. Because the lime in the ground means that the plant cannot absorb enough magnesium, iron and nitrogen.

Tip:

Lime can also accumulate in the soil through watering with lime-containing tap water. If possible, always water the rhododendron with rainwater.

Damage image

If the rhododendron suffers from chlorosis, the leaves become unevenly yellow, whereby the leaf veins can remain green. With chlorosis, also known as bleaching or jaundice, the plant cannot produce enough chlorophyll or it is even broken down. As the disease progresses, the leaves turn brown from the edge and eventually fall off.

Chlorosis / calcium chlorosis

Chlorosis usually begins on young leaves and spreads over the older leaves as well. The plant is beginning to worry. It is also extremely susceptible to fungal infections.

Common causes of calcium chlorosis in the rhododendron are:

• soil pH too high
• a lot of lime in the irrigation water or in the soil

To cure or heal the rhododendron To save it, the goal must be to enable the shrub to absorb iron as quickly as possible.

First aid for rhododendrons is iron fertilizers:

• Dissolve iron fertilizer in lime-free water
• Spray the leaves with the solution

You can also water the rhododendron with a solution of iron fertilizer and water. However, then the shrub cannot or does not absorb the iron very well. do not absorb as lime and a high pH value of the soil prevent it from being absorbed. Since the causes of calcium chlorosis lie in the soil, this must also meet the requirements of the rhododendron. So that the pH value drops, you should work bog bed or special rhododendron soil into the soil. In addition, you should cover the floor with needle litter.

Improvement of the soil

Often the saving earth cannot be worked into large shrubs because the soil is too deeply rooted. In this case, a pouring rim can serve to improve the soil.

• Dig the pouring rim around the trunk at a distance
• Fill the pouring rim with rhododendron soil

When watering, the substances that lower the pH value then get into the soil. However, the effect can only set in here after a few weeks. To do this, the process can be repeated several times without damaging the rhododendron.

Tip: If a soil sample shows that the location is no longer suitable for the rhododendron, you should consider moving the plant to a more suitable location.

Nitrogen deficiency

If the leaves of the rhododendron including the leaf veins are yellow, the shrub suffers from a nitrogen deficiency. Other signs of this disease are poor growth of regrowing leaves.

This form of chlorosis often occurs when the ground is covered with bark mulch without an underlying layer of horn shavings. In this case it is a nitrogen fixation, i.e. the plant cannot absorb nitrogen. The best way to combat the disease is with a fast-acting mineral fertilizer.

Tip: The last fertilization should be done at the end of May or mid-June. Nitrogen stimulates growth in the plant. In order for the shoots to survive the winter, however, they must be lignified, which takes a certain amount of time.

So that the rhododendron can absorb sufficient nitrogen, you should fertilize it with horn shavings over the long term. This is particularly recommended for rhododendron species that require a lot of nitrogen, such as rhododendrons-Catawbiense hybrids.

Magnesium deficiency

A lack of magnesium also causes the leaves of rhododendrons to turn yellow. This deficiency symptom can also occur in soils with an optimal pH value for the rhododendron, since in permeable soils the magnesium is washed out by rain. An Epsom salt fertilizer is suitable as first aid for the rhododendron.

• Spray the plant with a 2 percent solution of lime-free water
• Water the plant with a solution of water and Epsom salts

Tip: 150 grams of Epsom salt dissolved in 10 liters of rainwater lower the pH value of one square meter by one point.

Care errors

In addition to the deficiency disease chlorosis, there are also other causes of yellow leaves. They are often the result of incorrect care. In contrast to chlorosis, however, the consequences of care errors can be remedied more easily.

Lack of water

In hot, dry summers, the rhododendron gets yellow to light brown leaves relatively quickly, which curl up. This is a reaction of the plant to a lack of water. Spray the rhododendron with lime-free water and give it generous amounts of water. After that, the shrub should recover. If the leaves of the rhododendron have brown spots after hibernation, it was not watered enough in winter. The only thing that helps here is to wait and hope that he will recover over the summer.

sunburn

Has the protective shadow been taken from the rhododendron, for example by the omission or thinning of the shade-giving tree, too strong sunlight can cause yellow leaves or brown spots to lead.

Sunburn occurs:

• for leaves with direct sunlight
• with leaves that do not receive any shadow from other leaves

Since the leaves of the rhododendron are slightly curved at the edge, sunburn often only occurs in the center of the leaves.

Tip: Sunburn can also occur in sunny winters.

Quick help with sunburn is:

• Give rhododendron enough water
• Shade rhododendrons

Tip: A shading net or a garden fleece is suitable for shading.

Also, make sure that the shrub is very well supplied with water in the future.

Tip: If there is no way to naturally shade the rhododendron, it should move to a more shady spot.

Frost damage

In and of itself, rhododendrons tolerate the German winter very well. However, if the shrub is in an exposed location, wind and cold can bother it and its leaves develop brown spots. Cut off the frozen parts of the plant in spring and protect the rhododendron from the cold in the coming winter.

Yellow autumn leaves

With a few exceptions, rhododendrons that are planted in the garden are evergreen plants. Sometimes, however, the leaves begin to turn yellow in autumn. And a little later they fall off. This does not have to be a deficiency symptom; the shedding of some of the leaves can also be a natural process. Because even evergreen rhododendrons shed part of their oldest leaves every two to four years.

Tip: Even if it can be a natural process, check the plant as a precaution for deficiency symptoms or pest infestation.

Fungal infections

Brown spots on the leaves of the rhododendron are mostly caused by fungal infections. You can recognize an infection with the Phytophtora fungus by the brown spots that are lightly dried in the center. Other symptoms of the fungal infection are dead terminal buds and withering shoots. Leaf spot diseases mean the infestation of various fungi. Infection usually takes place in humid and warm summers, which is an ideal climate for fungi.

The causative fungi include:

• Glomerella
• Pestolotia
• Cercospora
• Colletorichum

Depending on the fungus, red-brown to brown-black spots form. Their shape is round or irregular. At the beginning of the infection the spots are relatively small. They only grow together as the fungal infection progresses.

For quick help:

• pluck off infected leaves
• Treat rhododendrons with fungicide

Tip: To prevent the fungus from spreading further, the leaves must be disposed of with household waste.