Planting rhododendrons: expert guidance & planting tips

Rhododendrons are a must-have in any garden. However, there are a few small things to consider when planting rhododendrons to give them the best start.

Rhododendrons (Rhododendron) are a huge genus within the heath family (Ericaceae) that includes over 1,000 species. At the same time, the geographical spread of the rhododendron extends over many continents. Despite the great diversity in origin, there are many parallels in terms of growing conditions. We reveal what you need to pay attention to so that your favourite rhododendron thrives magnificently and decorates your garden in full bloom.

Planting rhododendrons: when is the best time?

In principle, you can plant your rhododendron all year around as long as it is in a container. Root crops are planted in the spring or autumn. Planting in late spring (April or May) brings the advantage that by this time of the year the soil is already slightly warmed and the risk of night frosts is virtually eliminated. In addition, the soil is consistently moist enough for shallow-rooted rhododendrons to become well established. In addition, when you buy the plants you can already spot the first flowers and be sure of the flower colour. Planting in the autumn (early September to mid-November) brings the advantage that the roots form more quickly. At this time, your rhododendron will go into winter dormancy. As a result, all of its energy is put into the formation of shoots. This then encourages root formation.

Where to plant rhododendrons?

The rhododendron originates from high altitudes where, due to shallow soils, it can only develop a shallow root system. These soils are characterised by high permeability and, above all, a slightly acidic pH. Find out in the following section how to create the optimal conditions for your rhododendron in your own garden.

The right rhododendron soil

Rhododendrons require acidic conditions and under no circumstances should “suffocate” due to waterlogging. However, most soils in our latitudes tend to be neutral to slightly alkaline (for example, with limestone subsoils), so you should enrich your planting hole with plenty of compost.

In addition to acidic conditions, rhododendrons love loose, airy soil with high permeability. While some sites may have permeability (for example, on sandy soils or black earth), some gardens may need some help (for example, on loamy, clay sites). It is advisable to increase the grain size structure by adding sand. To do this, simply mix sand into the planting soil in a ratio of 1:1.

If you want to be on the safe side, you can also add a drainage layer of gravel to the bottom of the planting hole, or add larger quantities of bark mulch to the planting hole. This prevents waterlogging and regulates water drainage. However, despite the permeability, the soil should have a good water storage capacity.

Tip: Coffee grounds have proven to be a home remedy for fertilising acid-loving plants. This slightly acidifies the soil and also adds small amounts of essential nutrients to the soil.

Here we have collected additional information about rhododendron soil for you.

Planting rhododendrons in a pot

The conditions that rhododendrons like to find in the garden should also be observed when planting them in a pot. Be sure to use the widest container possible so that the shallow-rooted rhododendron can develop appropriately. Note: not all varieties are suitable for growing in pots or containers due to the differences in size. For example, the species of Japanese azaleas include many varieties that are relatively small in size and therefore ideally suited for growing in pots. Two special features must still be observed when planting in a pot: first, you need to make sure that waterlogging does not form in the pot. Therefore, use a pot with a drainage hole and place a layer of drainage at the bottom of the pot.

Secondly, overwintering is a bit of a challenge as the pot freezes through quite quickly due to the large surface area of the root ball. If you do not have the opportunity to place the rhododendron in a warmer location, try to protect it as much as possible from changing sunlight and cold drafts. It is best to place the container plant against a house wall, a closed fence or between other taller plants, so that the plant has protection from as many sides as possible. In addition, an insulating layer can minimise heat loss from the pot with which you can ensure good conditions for your precious plant even in winter. To do this, wrap the pot with several layers of bubble wrap or newspaper.

Planting rhododendrons: step-by-step

To ensure that your rhododendron grows and thrives quickly and safely after planting, there are a few things to keep in mind. We explain the key factors in a step-by-step guide:

1. Site selection for the rhododendron
Rhododendrons prefer semi-shaded sites with good water supply and especially prefer gentle slopes. You can also choose a full sun location for your rhododendron but you need to pay attention to proper water management. It should have plenty of distance from other plants in any location because the rhododendron develops an extensive and shallow root system.

2. Observe the correct planting distance of rhododendrons
Depending on the variety, rhododendrons can grow to be very sprawling. Therefore, it is important to maintain a sufficient distance from neighbouring plants. If many rhododendrons are planted next to each other, the appropriate planting distance should be maintained otherwise the shallow roots will interfere with each other. Here, the planting distance is chosen depending on the size at planting time and the expected final size. Depending on the size, there should be 30 (low-growing varieties) to 100 (high-growing varieties) cm of space between the edges of the crown. If the rhododendron is to form part of a hedge (for example, the ‘Bloombux’ variety), it is quite possible to do without large planting distances. If the plants do grow too close together, they can simply be replanted to increase the spacing.

3. Dig a large enough planting hole for the rhododendron
As described previously, rhododendrons require particularly permeable and acidic soil conditions. The larger the planting hole, the more loosened soil surrounds the roots of the freshly planted rhododendron. Therefore, the excavated planting hole should be at least twice or, even better, three times the circumference of the root ball.

4. Prepare the plants
The root ball is watered intensively before planting by immersing it in a container of water until no more air bubbles appear.

5. Prepare the soil for planting
Depending on what soil conditions you have in your garden, some adjustments may be needed to give your rhododendron the perfect start. In any case, the excavated soil is mixed with humus in a ratio of at least 1:1. This provides the nutrients and lowers the pH value. The pH can be adjusted to about five by the amount of humus but also with coffee grounds.

Loamy and clay soils are unsuitable for growing rhododendrons because they have too dense a particle size spectrum and tend to be in the alkaline pH range. Thus, the planting hole should be enriched beforehand with abundant sand to create a permeable environment. If you want to be on the safe side when caring for your rhododendron, you can also replace the entire hole with special rhododendron soil. This has all the qualities that your rhododendron needs to be happy.

6. Put the rhododendron in the planting hole
Do not place the rhododendron too deep into the hole. Otherwise, the roots cannot be properly supplied with oxygen and the plant will die. Fill the planting hole so that two inches of the root ball still peek out of the soil. Tread the soil only lightly to keep it nice and permeable.

7. Water and fertilise the rhododendron well
After planting, water the rhododendron vigorously. You can also create a watering rim to make watering more effective. To give your rhododendron the best start, fertiliser such as bone meal or compost can be worked into the surface after planting. This nitrogen-heavy fertilisation counteracts nitrogen deficiency by creating a decomposing mulch layer. Our Plantura Hydrangea Food is also excellent for rhododendrons.

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8. Mulch after planting
Once the rhododendron is planted, another layer of mulch is applied to the root zone. This protects against dehydration, temperature fluctuations, prevents weeds in the root zone and keeps the pH value down when decomposing.

9. Rhododendron care after planting
In general, the rhododendron is relatively easy to care for but this is only true as the plant ages. A young rhododendron requires regular watering but without drowning in waterlogging. Regular watering will accelerate youthful growth and help your rhododendron become established. Here, the rhododendron needs above all time to form an extensive root system so that it can survive any dry summer months in the next few years without watering. Fertilise for the first time two weeks after planting, if planted in the spring. If planted in the autumn, fertilise for the first time the following spring.

For more information on rhododendron care, click here.