Rhododendron care: expert tips on watering, fertilising & pruning

Rhododendron blooms are a favourite among many gardeners. However, to ensure lush flowering it must be properly cared for and protected from disease. Find out all about rhododendron care.

Rhododendrons (Rhododendron) are one of the largest genera within the heath family (Ericaceae). With more than 1,000 species worldwide, the rhododendron is geographically represented almost everywhere. Therefore, it is not surprising that it can be affected by a variety of pests and diseases. We provide tips on proper care and effective control of pests and diseases so that your rhododendron can continue to bloom in full splendour.

Rhododendron care

Rhododendrons are relatively easy to care for. However, they do require some attention from you at certain times of the year. We reveal what you should pay attention to when caring for them. However, before we get started, it should be said that there are certain points to consider before even planting a rhododendron. Rhododendrons prefer a slightly acidic soil and detest waterlogging. However, many soils, especially in southern Germany, tend to be neutral to slightly alkaline. Therefore, it may be advantageous to dig a generous planting hole and fill it with a special rhododendron soil.

Watering rhododendrons

Rhododendron plants require regular watering, particularly when they are still small. However, waterlogging must not be allowed to occur as the rhododendron, being a shallow-rooted shrub, is very sensitive to this. The larger and older the rhododendron becomes, the less often it needs to be watered because the roots are now more developed. Signs of the need for watering may be drooping buds during flowering, or else curling leaves.

Note: water your precious plant at slightly longer intervals but with a little more water. During dry spells in particular, too small amounts of water can evaporate quickly before penetrating the soil.

Fertilising

Rhododendrons are especially happy with long-term fertilisation. The best time for this is in the spring, which means shortly after planting for freshly planted shrubs. Work the fertiliser superficially into the root zone so that the nutrients can be better absorbed into the soil. Also, while you are still planting, mix bone meal, compost and/or coffee grounds with the excavated soil and then return it to the planting hole. These fertilisers are all purely organic, have slightly acidifying properties for the soil and have a positive effect on soil life. While coffee grounds lower the soil pH but are not a very great nutrient supplier, compost does the job of delivering long-term nutrients. Bone meal does not affect soil pH but also provides long-term nutrient release with a high nitrogen content. For those who prefer to fertilise regularly rather than rely on slow-release fertilisers, discontinue fertilisation in early October to induce dormancy.

For your favourites that are already well established in the garden, experts recommend giving the shrub an energy boost a few weeks before flowering with a mixture of mineral and organic fertiliser. Learn more in this video.

In addition to the above home remedies, there are also special rhododendron fertilisers on the market, which cover the entire spectrum of nutrients and also replenish (some fully organic) nutrients in the medium term. A plant-based fertiliser such as our Plantura Hydrangea Food is also suitable for rhododendrons. The slow-release fertiliser gently releases its nutrients to the rhododendron over a longer period of time and also provides it with iron.

Note: Under special circumstances, a second fertilisation may also be carried out in the summer. This is only necessary if a lack of nutrients manifests itself in the form of yellow and withered leaves.

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You can find out more about how to properly fertilise your rhododendrons here.

Pruning rhododendrons

In principle, rhododendrons do not need special pruning to bloom profusely. However, over time it will experience increased lignification of the shoots, so rejuvenation pruning as needed makes perfect sense. Radical rejuvenation pruning should be done before flowering because you will not unnecessarily waste the energy reserves of your rhododendron and nesting birds will not be disturbed.

Using sharp rose shears, cut off any old shoots so that the bare interior of the bush receives light again. It is important to make sure that you cut the shoots at an angle. This will prevent dew or rainwater from collecting on the open parts of the shoots, which could possibly allow diseases to penetrate. If you do not want to perform a radical rejuvenation pruning but just want to maintain the shape of your rhododendron, you can do a comprehensive maintenance pruning right after flowering. This involves removing unsightly, diseased and injured shoots until you are once again satisfied with the growth habit of your favourite plant.

We have put together more tips and tricks for pruning your rhododendron here.

After flowering: deadheading rhododendron flowers

After you have done a comprehensive pruning, you can still continue to do something good for your rhododendron. To do this, simply deadhead all the withered flowers on the remaining shoots. This promotes bud formation the next year and eliminates spore foci, which prevents infestation by fungal pathogens.

Rhododendron diseases

The rhododendron genus is particularly susceptible to fungal diseases but animal pathogens also wreak havoc on the rhododendron’s evergreen foliage.

Rhododendron has yellow and brown leaves

The discolouration of the leaves usually has two causes: either the plant was improperly cared for or it was attacked by a fungus. In order to do something about the discolouration, the source of the damage must first be identified. Chlorosis from improper care can be caused either by soil that is too calcareous or by a nitrogen deficiency. In fungal infections, different yellow or brown lesions form depending on the pathogen.

Here you will find a listing of common fungal diseases of rhododendron, as well as any diseases that may occur due to animal pathogens.