A healthy magnolia shows large, bright green leaves, which in many species cultivated in this country turn yellowish in autumn and are shed. However, if the foliage of the deciduous magnolias turns brown or yellow in spring or summer, the cause is usually to be found in an unsuitable location and/or incorrect care. Furthermore, fungal diseases or pests can be considered as the cause, although these rarely appear.
brown leaves
Browning of the magnolia leaves can have various causes, but these are mostly due to an unsuitable location and/or incorrect care. Before you take hasty countermeasures based on a suspicion, you should first carefully find out the actual cause: Sometimes completely opposite phenomena lead to the same symptoms, which is why a purely symptomatic instead of a causal treatment can end deadly for the tree.
Nutrient deficiency / over-fertilization
A good example of a confusing set of symptoms is the fact that both a lack of certain nutrients and over-fertilization will cause the leaves to turn brown. Take a close look, because the specific type of discoloration often reveals the cause:
- Leaves turn brown first at the edges, then towards the inside: Potassium deficiency
- brown discolored leaf edges: over-fertilization
- brown and dried leaves: alkaline and/or calcareous soil
measures
In the event of a potassium deficiency, fertilize the magnolia with a potassium fertilizer from the garden supply store, which you gently work into the root disc with a rake and then water the tree vigorously. Watering is especially important because the fertilizer gets to where it belongs so quickly: to the roots.
Brown discolored leaf edges, on the other hand, often indicate over-fertilization, where you have to act quickly: The only thing that often helps here is to thin the soil with sand or to transplant the magnolia to another location. However, this should really be the last option, because the sensitive plants do not like transplanting at all. They often react to this by dropping their leaves or even dying.
The magnolia feels most comfortable in a slightly acidic substrate, which is why it reacts quickly to an alkaline substrate and its foliage turns brown and dries up. Remedy by giving plenty rhododendron soil Spread around the tree and work it lightly into the soil. Then you should water well!
drought/ waterlogging
If the magnolia seems to be drying up and the foliage is therefore turning brown, is thrown off later and even whole twigs and branches wither, do not immediately reach for the watering can. This phenomenon occurs not only due to severe drought, but can also be the result of a waterlogging appear. If the magnolia is permanently in moist soil, the roots will begin to rot after a while and can no longer absorb water or nutrients. The above-ground parts of the plant literally starve and die of thirst because moisture is no longer transmitted. Waterlogging occurs mainly in heavy soils, but can also be a result of well-intentioned watering behavior or heavy rainfall. On the other hand, magnolias are threatened by water shortages, especially during longer dry periods, especially during flowering and during the hot summer months. This is especially true if you are standing on an already rather dry surface.
countermeasures
- Dryness: water vigorously and regularly, do not use tap water (calcareous!)
- Waterlogging: dig up the magnolia, severely cut back rotting roots and above-ground shoots, move to a new location
tip: Always cut back trees and shrubs to be transplanted by a third, as the plants always lose part of their roots and the branches and shoots therefore have to be cut back accordingly. Otherwise there may be supply bottlenecks, since the remaining roots can no longer supply all parts of the plant with sufficient water and nutrients.
root damage
However, the causes of leaf discoloration are not always in things that you could influence: Sometimes only pests such as grubs or vine weevils have an appetite for magnolia roots, which is why they eat them and the plant can no longer absorb enough water and nutrients. In addition to the pests mentioned, the roots of the magnolia also taste very good to voles. If you have such a suspicion, take a closer look at the root system and the soil. The roots show signs of being eaten, while you can find thick maggots or the underground passages of the polluters in the soil.
measures
Basically, the only thing that helps against voles is to plant the magnolia within a protective cocoon, for example made of close-meshed wire mesh, or to cultivate the tree in a large bucket. Above all, it helps against the light-colored larvae of the vine weevil - a beetle that in its adult form prefers to eat holes in leaves - and against grubs nematodes, which you can buy in specialist shops and spread directly in the affected root area. The bacteria penetrate the bodies of the larvae and kill them within a few days.
ridged weevil
late frost
If not only the leaves but also the buds and new shoots are discolored and dried up in spring, the cause is to be found in the late frost. Especially the young shoots, the buds and the flowers do not tolerate frost and must therefore be protected in good time. There is currently nothing you can do in this case, just cut back the frozen parts of the plant and hope for next year. Give the frozen tree some fertilizer, for example in the form of rhododendron soil spread around the trunk to encourage new shoots.
Leaves have brown spots
Sometimes the leaves of the magnolia do not have a uniform brown color throughout, but rather individual brownish spots or dots. These are often caused by fungal pathogens, but not in all cases.
magnesium deficiency
A magnesium deficiency can often be observed in magnolias, after all they mainly grow on soils with a rather acidic pH value - and these, in turn, usually contain little magnesium. In addition, many commercially available universal fertilizers contain no or too little of the mineral, so that a deficiency is practically inevitable.
Signs of magnesium deficiency
- yellow-green discoloration of the foliage
- brownish leaf spots
countermeasures
A magnesium deficiency can be easily eliminated, all you have to do is fertilize the magnolia tree with a commercially available special fertilizer according to the manufacturer's instructions. Epsom salts or magnesia work best for this purpose.
leaf spot disease
Leaf spot disease is manifested by brownish to black leaf spots, which are often surrounded by a yellowish ring. It occurs primarily during the summer months in cool (approx. 15°C to 20°C) and damp weather and is transmitted by rainwater. This is where the causes of the disease cavort, which are bacteria of the species Pseudomonas syringae. An infestation must be treated, because as the disease progresses, the infection spreads to shoots and branches, which dry up and die.
countermeasures
In the event of an acute infestation, all you can do is remove the infested parts of the plant as quickly as possible with clean, sharp pruning shears or another suitable cutting tool. You should neither compost the clippings nor simply leave them lying around in the garden. The bacteria hibernate in it and can spread further from their new location. Instead, burn the cut plant parts or dispose of them with household waste.
tip: Prevention is the best way to combat the common leaf spot disease. Make sure that the magnolia is in an airy location, has enough space on all sides and its crown is not growing too dense. The leaves must be able to dry off quickly after a downpour so that any bacterial pathogens have no chance of getting in.
Leaves curl/curl
It is also advisable to look closely if the magnolia leaves suddenly curl or curl inwards from the edges. There are also various reasons for this.
dryness
The curling of the foliage is a typical protective mechanism that prevents the plant from evaporating valuable moisture in dry conditions. As the magnolia tree reduces the leaf surface by rolling or even curling, less water is released into the surrounding air. This mechanism often occurs during longer periods of drought and especially during the hot summer months. It is practically the preliminary stage before the foliage and shoots dry up due to lack of water.
countermeasures
Gently loosen the soil around the magnolia stem with a garden hoe on. Be careful not to damage the roots just below the surface. Then water the thirsty tree thoroughly. Repeat this measure in the following days and weeks. You can also mulch the root area and thus keep the moisture in the soil longer.
pests
However, before you water the magnolia completely unnecessarily, first carefully examine the leaves, which have been deformed by rolling or curling, for pests. Pests that suck leaf juice, such as aphids, scale insects or whiteflies, should be driven out urgently, as they are often carriers of fungal diseases - or cause other problems, such as an ant invasion or a stubborn sooty mildew fungus. An infestation is often indicated by yellowish to brownish leaf spots.
countermeasures
If the pest pressure is not too pronounced, spraying with a self-made nettle decoction often helps. Repeat this measure several times at intervals of a few days. In the case of a severe infestation, however, only an insecticide suitable for outdoor use will help. Dilute this with water and you can treat larger areas effectively.
tip: Beneficial insects such as assassin bugs, earwigs or ladybugs are the best help against pests. Build a comfortable insect hotel near the magnolia tree and prevent an infestation with aphids and the like.