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No matter whether in the garden or in the tub, hydrangeas are extremely decorative ornamental shrubs with a stately size. Between June and August they impress with their large, magnificent flowers. Under optimal conditions, these attractive shrubs are relatively hardy and hardly susceptible to diseases and pests. However, unfavorable site conditions or errors in care can significantly increase or promote the susceptibility of these plants to a wide variety of diseases or pest infestation.


Common problems with hydrangeas

There are evergreen and deciduous species of the hydrangea (Hydrangea), which differ in growth height, size, shape and color of the flowers and leaves. The most popular are the varieties of farmer's hydrangea. If the hydrangea feels comfortable in its location and if it is cared for according to its needs, it shows all its splendour. However, even they are not immune to diseases. Weakened plants are particularly at risk.

Peasant hydrangea in the garden


Diseases can occur, among other things, when the pH value of the soil is unfavorable, the soil is too nutrient-poor, too nutrient-rich, and permanently too wet or too dry. If the location is too dark or too sunny, the plant will suffer. In addition to incorrect care and deficiency symptoms, unfavorable weather conditions can promote fungal infestation. Viruses and bacteria can also attack the plants and cause viruses or other diseases. Not to forget plant pests such as spider mites, aphids, vine weevils or thrips, they too can make life difficult for hydrangeas.

treatment options

Mostly weather-related fungal diseases

Fungi are usually the result of unfavorable weather conditions. Then they can attack hydrangeas and other plants and spread relatively quickly. If a corresponding infestation is detected, it is important to react quickly in order to prevent it from spreading. It is all the more important to pay attention to optimal location and husbandry conditions.

Hydrangea with brown mottled leaves

Powdery and downy mildew

Powdery mildew is one of the diseases that can affect hydrangeas. This so-called bad weather fungus occurs above all in the event of strong temperature fluctuations, with excessive humidity in particular playing a decisive role.

  • Infestation can be recognized by a whitish-grey, mealy coating on the undersides of the leaves
  • Upper leaf surfaces covered with characteristic powdery mildew spots
  • Fungi spread very quickly over the entire plant
  • If there is an obvious infestation, start combating it as soon as possible
  • heavy infestation can hardly be combated effectively
  • as a first measure, completely remove affected leaves and shoots
  • Always dispose of clippings with household waste or burn them
  • then treat with a suitable fungicide
powdery mildew on a plant

Affected leaves that are already lying on the ground must also be removed. In the case of an initial infestation, multiple sprayings with plant broths made from horsetail or tansy can be used to combat it. In addition, the use of beneficial insects such as ladybugs or sawflies is a good idea.

Gray mold (Botrytis bud rot)

Gray mold is also caused by a fungus. Cool, damp weather and spray can encourage infestation. It can be recognized by a gray lawn of mold on the flower buds, leaves and shoots. Often there are also brown inflorescences. Affected plant parts must be removed and the hydrangea then treated with suitable sprays. As a preventive measure, ensure good ventilation by regularly thinning out the plants inside. If necessary, transplanting into a lighter soil can help.

Gray mold infestation

care mistakes

Illnesses as a result of care errors or deficiency symptoms

In most cases, problems with hydrangeas can be traced back to poor growing conditions. The good thing is that diseases like chlorosis or leaf spot can be controlled very successfully with improved conditions and the plants usually recover quickly.

chlorosis/yellowing disease

The cause of chlorosis can be a lack of nitrogen, potassium, magnesium or iron, but also a persistent lack of water. Signs of chlorosis are yellowed leaves from the tip, which turn brown in the advanced stage. Older hydrangeas usually lack nitrogen, potassium and magnesium.

If such leaf damage occurs on freshly sprouted leaves, an iron deficiency is usually the cause. This mainly occurs in soils with a high lime content, which means that the plants cannot absorb enough iron, which leads to a deficiency. Red or pink varieties are particularly often affected because they depend on a slightly acidic pH value in the soil.

  • Before using any fertilizer, soil analysis recommended
  • Analysis provides certainty about which nutrients the plant is lacking
  • If there is a lack of nitrogen, add nitrogen in the form of a fertilizer
  • when dosing, follow the manufacturer's specifications
  • In soil that is too calcareous, incorporate peat, rhododendron earth or leaf compost
  • this makes the soil a little more acidic
  • Eliminate iron deficiency by administering an iron-containing foliar fertilizer
  • future use of special hydrangea fertilizers can prevent diseases
Hydrangea with brown leaf edges

Tip: Over-fertilization should be avoided at all costs, as it can sometimes cause even greater damage to the plants.

Leaf spot disease/leaf spot fungi

A lack of nutrients, together with excessive humidity, can promote an infestation with leaf spot disease. It manifests itself in yellowish leaves, which are covered with dark spots of different sizes. Each of these spots has a brown center. As the process progresses, the leaf tissue thins out and the leaves fall off.

Here, too, infested plant parts and those lying on the ground should be completely removed and disposed of with household waste. This is the only way to avoid reinfection. If the infestation is severe, it may need to be treated with an appropriate fungicide. In order to prevent infestation with leaf spot fungi in the future, it is advisable to thin out the hydrangea regularly and to avoid plant populations that are too dense. This is the only way the leaves can always dry quickly. In addition, it is important to ensure that fertilizer is used as needed.

Hydrangea with yellow leaves

root rot

Root rot is also one of the diseases that can affect hydrangeas. They are usually the result of too much moisture. The affected plant shows yellowed, wilted and drooping leaves, the root eventually dies. The hydrangea shows stunted growth, hardly produces any flowers and only weak shoots. Before root rot is identified as such, it is usually too late and the plant can no longer be saved.

If it is nevertheless detected early, the affected plant must be dug up immediately and rotten root parts removed. Before planting, a drainage layer of gravel or coarse sand should be placed in the planting hole, which is then filled with special hydrangea soil and the hydrangea is reinserted. You should then refrain from watering for the time being.


Hydrangea virose

The so-called hydrangea virus can be caused by both bacteria (mycoplasma) and viruses. It can be recognized by its clearly restricted growth, or by the fact that the plant and flowers remain very small. In addition, the leaves become dull and take on a purple to reddish color. It is not possible to combat such highly contagious diseases, so that affected plants must inevitably be disposed of. Not only the plant itself but also the soil in which they stood must be generously replaced.

Tip: Replanting the hydrangea (Hydrangea) in the same place is advisable after 4 - 6 years at the earliest.


In addition to diseases, hydrangeas can also be attacked by pests. Infestation is most evident on leaves and flowers. Here, too, it is important to regularly check the plants for an infestation in order to recognize it as early as possible and to be able to start combating it.

spider mites

Spider mites are one of the most common hydrangea pests. They can be recognized by small silvery-white dots on the upper side of the leaves and later by the typical fine webs on the undersides of the leaves. The leaves usually curl up. Spider mites can settle most easily if the soil is permanently dry and the plant is exposed to direct sunlight.

Spider mite infestation

To combat it, the first thing to do is to thoroughly rinse the plant. In the case of a light infestation, this is usually sufficient. If not, they can be treated by spraying them with sprays containing rapeseed oil. In order to prevent future infestation, it is recommended to move to a better, preferably partially shaded location in evenly moist soil.


If the plants are weakened by heat, drought or a lack of nutrients, they can also be attacked by aphids, although this is not uncommon.

  • Infestation occurs mainly in spring when it is warm and dry
  • sticky honeydew on the leaves, signs of an infestation
  • Lice infestation attracts ants
  • this promotes the occurrence of sooty mold
  • Sooty mold can be identified by a sooty coating on the plants
  • first control measure, spraying the plant
  • Rinsing off with initial infestation is usually sufficient

If all lice have not yet been expelled, you can spray the hydrangea with home-made, diluted nettle manure. Since lice usually spread explosively, commercial sprays can also be used if necessary.

aphid infestation

root nematodes

So-called root nematodes thrive in depleted soil. If they are present in large numbers, they can severely damage the roots of the hydrangea. An unpleasant odor near the ground may indicate the presence of these pests. If the roots are already damaged, parts of the plant near the ground will sag until they finally die.

Fighting is not possible. However, there are a few things you can do to prevent it. So you should pay attention to a needs-based supply of hydrangeas with nutrients. It can also make sense to plant marigolds (marigolds) between the hydrangeas, which can successfully combat soil fatigue caused by nematodes.

vine weevil

The vine weevil likes to attack the leaves of hydrangeas, while its larvae prefer the roots. Eating marks on the leaf edges can be a sign of an infestation. If the roots are damaged, the plant shows this by a lack of growth.

There are no special means of combating it either. However, you can collect the approx. 2 cm large black beetles. Or you can place a flowerpot filled with wood wool upside down under the bush. The pests retreat there overnight so that they can be removed the next day. The larvae on the roots can be controlled with nematodes.


Also known as blister feet, thrips are tiny, 1 - 3 mm small, dark brown, winged pests. Their larvae have no wings. This pest can develop particularly well in a dry environment. It sits mainly on the underside of the leaves of the hydrangea. These sucking insects leave yellowish spots on the leaves, which later turn silvery-white from the penetrating air.

In an advanced infestation, the leaves are heavily mottled. If you take a closer look, you will also discover small black dots on the leaves, the excretions of the pests. Special systemic agents for combating thrips are available on the market. In addition, the use of natural predators such as lacewings or assassin bugs is a good idea.


Snails can cause great damage to a wide variety of plants, including hydrangeas. They disdain neither the foliage nor the flowers and can eat plants completely bare within a short time, whereby snail species such as the Roman snail prefer to attack the withered foliage. Snails appear more often in damp weather. Plant remains on the ground can also attract these animals.

Snail in the garden bed

Combat is usually difficult. Special slug pellets are available on the market that can be spread around the plants. Of course you can read the animals again and again, but this is not for everyone. The best way is prevention. For example, you can mix dry straw with the mulch material. The mulch layer should rather be a little thin than too thick. Since snails are mainly active in the evening and at night, you should avoid watering in the evening and prefer to choose the morning hours instead. In addition, you should avoid sprinkling or watering upside down if possible, so that the leaves can always dry off quickly, because snails particularly like fresh, damp leaves.

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