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With its beautiful flowers, oleander (Nerium oleander) is one of the most popular tub plants. The plant, also known as rose laurel, is evergreen and impresses with leathery, dark green leaves even when not in bloom. Depending on the variety, these can reach a size of up to 24 centimetres. However, if the leaves suddenly turn brown, the cause must be investigated. Diseases or care errors can be shown by discoloration or dry leaves.
leaves and flowers
The leaves of a healthy oleander plant appear a dark, rich green. The plant, which originates from the Mediterranean region, is leafy all year round. The leaves only die off when the temperature is very low. Therefore, a cool, dark room with a temperature of 5 to 10 degrees Celsius is recommended for wintering.
Depending on the variety, the flowers of the rose laurel appear in white, yellow, pink or purple. Wild oleander bears purple flowers.
danger: Oleander belongs to the dogbane family. All parts of the plant are highly toxic!
Causes of leaf discoloration
If the foliage of the oleander changes color or becomes blotchy, it is usually due to incorrect care, excessive exposure to the sun or diseases.
- Lack of moisture
- over-fertilization
- too much sun exposure
- Infestation with oleander canker
- Blight/ Ascochyta
1. Lack of moisture
Dried leaves are a sign of a lack of moisture. Because the oleander must be sufficiently watered for a beautiful bloom and healthy foliage. Avoid drought stress, which is detrimental to plant development. If you notice dry leaves, you can save the plant by taking appropriate measures. Submerge the oleander in water until the root ball is soaked and no more air bubbles rise. Make sure that the substrate is always moist enough.
tip: Never water the rose laurel in full sun!
2. Over-fertilization
Excessive fertilization can lead to brown leaf discoloration. If you see brown spots and suspect a fertilization error, you can remedy the situation with a potted plant by rinsing it out vigorously. Water the potted plant and make sure that the water can drain off well. It is best to remove the saucer or the planter.
Do not fertilize in the following weeks. Do not fertilize again until the plant has recovered well.
tip: "A lot helps a lot", that definitely doesn't apply to fertilizing! The correct dosage is particularly important for potted plants. Due to the limited amount of substrate, over-fertilization cannot be compensated for and quickly leads to damage to the plant.
3. Too much sun after hibernation
Oleander overwinters well in a cold basement. If you free it from winter quarters in spring, you should examine the plant carefully, because some diseases prefer to develop in winter. If you put the plant outdoors, it should also be at night no frost to be feared. Above all, you should not place the plant in direct sunlight. Strong sunlight can cause discoloration of the leaves. Choose a shady place where the potted plant can slowly get used to the new location.
4. Oleander crab (Pseudomonas)
A bacterial disease called oleander canker is a common cause of brown spots on oleander leaves. The trigger for this is the bacterium Pseudomonas syringae pv. savastanoi. The disease does not have to lead to the death of the plant if you act in time. Symptoms of oleander canker can include discoloration, crippling and deformation of inflorescences, buds and shoots. The manifestations are different. First, changes appear in the most sensitive parts of the plant, the buds and flowers. These can turn dark, do not bloom and fall off. After that, brown spots appear on the leaves. These spots become dry and crack.
Measures against oleander canker
So far, no drugs against oleander canker are available. The only way to combat the disease is to cut back radically. Cut back all clearly affected shoots down to the healthy wood. You can leave shoots that show only slight signs of oleander canker, they usually recover well. Be sure to sterile cutting tool to use.
Attention, aphids also transport the Pseudomonas bacteria. Eliminate them with a solution of 1 liter of water, 2 tablespoons of soft soap and some spirit. Spray the solution on the plant every two to three days until aphids are gone.
tip: Plant parts affected by oleander canker are highly infectious. To protect other plants, you should therefore never compost the cut parts of the plant. Burn the parts of the plant or dispose of them in the residual waste bin.
5. Blight (Ascochyta)
Ascochyta disease poses a threat to oleander plants. This dry rot mainly appears on the inflorescences in winter. They dry up and die. The dry patches keep spreading. If the blight has progressed to the trunk of the oleander, the entire plant will die. Ascochyta is a fungal disease. The Ascochyta fungi form spores that penetrate the oleander tissue and continue to spread. Summers with a lot of rain are a great risk of disease. The Ascochyta fungi are spread by rain and watering.
Measures to be taken in the event of an Ascochyta infestation
If you notice an Ascochyta infestation on your plant due to deformations and dry spots, you should act quickly. Because you can still save your oleander! However, all parts of the plant above a visibly affected shoot can no longer be preserved. Therefore, cut off all affected parts of the plant and all shoots above.
Preventive spraying, especially in autumn before the start of hibernation, can protect against Ascochyta infestation.
tip: Injured tissue is an entry point for Ascochyta fungi and other oleander diseases. Seal all cut surfaces after pruning. In autumn, pruning should be avoided completely.