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Every year in spring, an otherwise boring bush is transformed into a real explosion of colour. Each rhododendron has its own personal shade in which it dips the numerous flower balls. Lovers of these plants cannot get enough of the beautiful sight and immediately put together a colorful collection. But does the bush need special building blocks for its flowers so that it never disappoints our expectations? Or may it be compost, horse manure and the like?

Fertilize rhododendrons

What requirements does the rhododendron have?

Rhododendrons love a balanced supply of nutrients and a low pH of 4 to 5.5. Many organic fertilizers lower the pH, making them ideal for fertilizing this variety of plants. However, if the pH is above 7.0, an organic fertilizer will not be enough to quickly bring it down to an acceptable level.
You should measure the pH value so that you know exactly whether the soil under your specimen is acidic enough. No special expertise is required for this, appropriate test strips are commercially available. If it is too high, you can lower it more effectively with an Epsom salt solution.

coffee grounds

Coffee grounds are a wonderful fertilizer for rhododendrons, which are produced daily and free of charge in almost every household. It contains all the important nutrients that this flowering bush needs. These are primarily potassium, phosphorus and nitrogen. But he has a few other advantages that the plant will also benefit from:

  • lowers the pH
  • attracts earthworms that loosen the soil
  • enriches the soil with humus
  • this is ideal for "lime opponents" and "hummus lovers" rhododendron

Since the quantities that are usual in households are not exactly lavish, it might be necessary to use other suitable fertilizers in the case of larger or more rhododendrons. Coffee grounds can easily be combined with other organic fertilizers, for example with horn meal. Always work organic fertilizers well into the soil so that the nutrients can be released by soil organisms suitable for plants. How to use this home remedy:

  • Coffee grounds that are still damp can become mouldy
  • leave to dry in a warm place
  • best spread flat on a plate
  • then collect in a large container
  • Fertilize rhododendrons with it twice a year

tip: You may also have the opportunity to get more coffee grounds. For example, you could ask for it in a café or ask your neighbors and acquaintances.

Compost without added lime

The domestic compost is welcome to almost every garden plant. It also offers a good combination of nutrients for the alpine roses, as the rhododendrons that grow in mountainous regions are called. But while it can be a well-mixed compost heap for most plants, this plant particularly benefits from leaf, bark, and coniferous compost. It is also important not to add lime when composting.

leaf compost

If you have a lot of oak leaves or leaves of beech and ash available in autumn, you can use them to make leaf compost yourself. This is perfect for the demanding rhododendron.

  • develops low pH
  • makes mineral fertilizers superfluous
  • apply from March to August
  • Spread a 5 cm layer under the bush every two weeks

The rotting of these leaves is very slow compared to normal garden compost, especially since calcareous compost accelerators have to be avoided. However, if you keep at it regularly and keep adding fresh leaves, after two years you will always have good compost on hand. Considering the long lifespan of an alpine rose, this waiting time is acceptable.

bark compost

Compost made from pieces of bark also lowers the pH of the soil. Particularly suitable are:

  • oak bark
  • bark of conifers

Before spreading, this compost should be mixed with clay and lime-free rock flour. A small amount of sand also increases permeability. Anyone who has no way of making this compost themselves or does not have the patience to wait for the long period of rotting can buy ready-made bark compost in stores. This costs about ten euros per 60 l, but should not be confused with the coarse bark mulch, which is mainly used to protect the roots from drying out. With bark compost you fertilize exactly as described above for leaf compost.

needle compost

Plant parts from conifers are usually not put on a compost heap because they lower the pH too much. However, this property is ideal for the rhododendron. Combined with horse manure, horn shavings and garden soil, the coniferous compost is an ideal fertilizer for magnificently flowering rhododendrons.

  • Fertilize during the growing season from March to August
  • Spread mixture around the root area
  • at intervals of 2-3 weeks
  • always incorporate

If the root area of your rhododendrons is covered with a layer of mulch, this must be pushed aside before fertilizing. Only then can it be incorporated into the soil.

horn shavings or horn meal

The coarse horn shavings and the fine horn meal are both good for caring for the rhododendrons. It is made from animal horns and hooves, the only difference being the different degree of crushing. The nutrients in the finer horn meal are available to the plants more quickly, while the coarse horn shavings are gradually decomposed over months.

  • cheap at around 3 euros per kg
  • available in every hardware store or garden center
  • occasionally also in supermarkets
  • a handful per rhododendron plant is enough
  • deploy in March

tip: Rhododendrons are flat-rooted. Stay just below the surface when working in the fertilizer to avoid damaging roots.

horse manure

If an opportunity presents itself to you to get horse manure for your garden, you should take it. Mature horse manure is ideal for fertilizing rhododendrons but also for many other plants in the garden. Mature manure also does not spread the odor that typically penetrates the nose in a cowshed.

  • only use mature crap
  • fresh manure can burn roots
  • approx. 5 l per square meter
  • deploy in spring
  • incorporate superficially

nettle manure

Sustainable gardening is popular and natural fertilizers are therefore becoming the focus of environmentally conscious gardeners. One of them is nettle manure. You can easily produce it yourself free of charge and is therefore also a great alternative to expensive special fertilizers in terms of price. Stinging nettle is available for free on every corner, only a little working time for collecting and preparing, as well as patience during the fermentation time are required. You can fertilize with nettle manure in between, but always diluted 1:10 with water.

  • 1 liter of water for every 100 grams of fresh nettles
  • put in an open bucket
  • just cover with a fine mesh
  • leave in the sun
  • stir daily
  • fermentation is over when no bubbles rise

tip: During the fermentation, the nettle manure stinks a lot. Add some rock flour to neutralize the smell as much as possible.


Ash from organic material is a suitable fertilizer for rhododendrons. However, only ashes from unpolluted wood or coal should be used for fertilization. With purchased fuel it is never quite certain whether it is not contaminated with undesirable substances.

  • only fertilize with cooled ash
  • Scatter ashes under the rhododendron

blue grain

This complete fertilizer contains all the nutrients that rhododendrons need, but in high doses. Therefore, care should be taken when fertilizing to avoid a harmful overdose. Also because blue grain can be washed out after fertilization and can quickly get into the groundwater. For the sake of the environment, this should definitely be avoided.

  • only fertilize with 40 to 120 grams of blue grain per square meter
  • exact amount depends on the size of the bush

Special fertilizers from the trade

If you don't have the time or desire, or perhaps no opportunity, to collect coffee grounds or create a compost heap, you can look around in the large fertilizer department of a garden center. Bark and coniferous compost are sold there, but also special fertilizers for rhododendrons. The latter have a combination of nutrients tailored to the needs of the alpine rose. Which specific fertilizer you buy is up to you, but be sure to pay attention to the following aspects:

  • pH lowering to pH neutral
  • low dosage of salts
  • but with plenty of potassium and phosphorus

tip: Yellow leaves indicate nitrogen deficiency. However, a high-priced special fertilizer from the trade does not necessarily have to be used, a simple nitrogen-rich fertilizer is sufficient to remedy this deficiency.

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