Rhododendron care: the most common mistakes

rhododendron flowering in spring
rhododendron flowering in spring

Caring for rhododendrons requires a little flair. If you avoid these mistakes, nothing will stand in the way of a lush abundance of blooms.

Rhododendron is one of the most beautiful flowering shrubs in the garden, but it also has some requirements in terms of location and care. The original forest plants thrive best in well-drained, humus-rich soils in partial shade. However, even if the location is well chosen: with the wrong care, it can sometimes happen that a rhododendron no longer blooms. Here are the most common care mistakes, and how to avoid them.

Fertilize rhododendron incorrectly

For a rhododendron to develop its beautiful dark green foliage and many flower buds, regular applications of nutrients are essential. However, not every product is suitable for fertilizing rhododendrons: If the fertilizer contains lime, it is better not to use it, because the shrubs are very sensitive to this nutrient, sometimes rhododendrons then have yellow leaves.

It is better to choose a special, preferably organic rhododendron fertilizer that is precisely tailored to the needs of the plants. The ideal time to fertilize is in March or April: spread the special fertilizer and/or horn shavings on the soil in the root area then. Coffee grounds are also highly recommended as an organic fertilizer: This has a soil acidifying effect and enriches the soil around the plants with humus.

Do not mulch rhododendron

Another important point in caring for rhododendrons is mulching. In their natural habitat in the forest, there is always a natural soil cover due to regular leaf fall. In our garden, too, flowering shrubs love it when a layer of autumn leaves or bark compost is applied to the soil: The mulch layer keeps moisture in the soil, suppresses weeds and enriches the substrate with humus. If the maintenance measure is forgotten, the soil may become too low in humus over time. Since mulch decomposes after one to two years, it should be replaced annually. For fertilizing, the mulch layer is only removed briefly and then reapplied or renewed.

Pruning rhododendron in spring

An older rhododendron that is becoming bare from below can be brought back into shape by pruning. However, do not prune your rhododendron prematurely: only when the flowering shrub is really firmly rooted in the garden will it tolerate a vigorous rejuvenation cut. In addition, the timing of the pruning should be well chosen. If it is done in the spring, it is at the expense of the flowers, because rhododendrons already form their flower buds in the previous year. Therefore, if at all necessary, pruning is recommended immediately after the withering of flowers. In this way, you can also counteract the spread of the rhododendron cicada: When they lay their eggs in late summer, the females like to transfer a fungus to the plants that leads to black, dead flower buds.

Do not remove brown buds in winter

The flower buds of your rhododendron turn brownish to black during the winter? If so, the plant is probably suffering from the fungus Pycnostysanus azaleae, which is often transmitted by the rhododendron cicada. The infected buds dry up and die, but remain attached to the branches. If the affected buds are not removed in time, the fungal disease can spread further. Therefore, always keep an eye on your rhododendrons in the garden: If brown or black flower buds appear on the plants, you should break them out in time and dispose of them in the household waste.

Watering rhododendron with tap water

Mistakes when watering a rhododendron can also have unpleasant consequences. As shallow-rooted plants, evergreen shrubs depend on consistent soil moisture. Regular watering is especially important in the first year after planting a rhododendron and during prolonged drought. The plant evaporates some moisture through its large leaves. However, do not use tap water for watering rhododendrons – it contains too much lime for the sensitive woody plants. Repeated watering with calcareous water raises the pH in the soil, which can lead to chlorosis, recognizable by a yellowing of the leaves. Ideally, therefore, rainwater should be used for watering rhododendrons. If this is not available, the watering water must necessarily stand longer or be decalcified.

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