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If the rhododendron does not bloom despite buds and leaves, this can have various causes. This article describes the most important ones and gives practical tips. In some gardens there are (apparently) healthy, lush leafy rhododendrons. They grow and thrive, but don't bloom. It is often very difficult to find the cause of this. The explanations in the guide can help with diagnosis and treatment.

Rhododendron Cicada

The most common reason why rhododendrons do not bloom despite buds and leaves is an infestation by the so-called rhododendron cicada (Graphocephala fennahi). Here is an overview of the characteristics of the insect feared by many hobby gardeners.

  • 8 to 9.5 mm long
  • strikingly green in color
  • red striped wings

About the procedure or process:

In late summer or fall, the rhododendron planthopper lays its eggs under the scales of the new flower buds of the rhododendron plant. As a result, small wounds appear on the buds. These serve as a portal of entry for a harmful fungus that is transmitted and spread by the insect. After infection with the harmful fungus, decay takes its course.

Notice: Weakened rhododendrons - such as those that are planted in an unfavorable location - can become infected with the fungus even without the involvement of the cicada.


During the winter, the buds of the plants turn brown and die off by spring. In addition, black, spiky fungal fruiting bodies develop on the infected buds. Although these bodies are very small, their dark color makes them immediately noticeable.

Once the damage has been done, the only thing that usually helps is to generously remove the infected buds. However, it then usually takes at least two years before the rhododendrons can bloom again. For this reason, it is advisable to initiate suitable control measures a few weeks before the potential infestation. Experts advise preparing the plants accordingly in the summer. From around September, the adult females of the rhododendron cicada are ready to fulfill their egg-laying mission. Once the case occurs, the flower for the next year is lost. Therefore, the animals should be baited in advance.

Tip: Glued yellow boards from the garden trade are ideal for attracting and catching the insects. One trap per rhododendron plant is sufficient.

crop protection products

Treatments with approved pesticides can also be considered. It makes sense to get active early in the morning. At this point, the cicadas are not yet fully active. This gives the hobby gardener a better chance of catching the animals.

Important: It is essential to ensure that you not only wet the buds sufficiently, but also the undersides of the leaves.

The measures described will help reduce the risk of fungal infection. If it does occur, it is probably due to external conditions that are not conducive to the plants. Always break out diseased buds after discovering them and dispose of them to avoid spreading the fungus.

negative influences

Wrong "framework conditions"

In addition to the cicada infestation, there are some unsuitable "framework conditions" that can ensure that rhododendrons do not bloom as hoped.

The possible negative influences at a glance:

1. inappropriate pot size

2. unsuitable soil

3. wrong location

4. unloved weather

To 1: A pot with a diameter of more than 30 centimeters is elementary. Rhododendrons quickly become too small in smaller pots.

To 2: The plant does not always do well with normal potting soil. It may be that it refuses to flower for this reason.

Tip: Peat is perfect. So-called rhododendron soil is commercially available - but it is also peat soil. So you don't necessarily have to buy a product that is offered directly under the plant name.

To 3: Sometimes you read that hobby gardeners keep their rhododendrons indoors, for example in a bright basement. This is NOT species appropriate. The beauties belong in the garden, even in winter.

Tip: Many plants in the temperate zone, including rhododendrons, need the cold to stimulate flowering. So you have to experience the cold phase, so to speak, to mentally check it off and then go on to bloom. If this cold phase does not take place, the plants constantly think: "It's still going to be cold, so I have to hold back". Incidentally, the same applies to most fruit trees.

The location itself should be fairly sunny, but not full sun. Rhododendrons are extremely sensitive to very dry root balls. Acidic soil is also important. It is best to measure the pH value with test strips from specialist shops and, if necessary, acidify the substrate - ideally with sulfur flower (powdered sulphur).

Tip: Do not use aluminum sulfate or alum. Larger aluminum concentrations are toxic to plants.

To 4: Rhododendrons do not cope well with the following weather conditions.

  • cold spell in autumn
  • long winter (danger of frostbite), for most rhododendrons a low temperature is known - this states to what degree (in the truest sense) the flower buds of the plants can survive or at what temperature they are damaged so much that flowering becomes impossible - the exact value depends on the species - so it is best to find out how your own rhododendron is doing in this regard, so that you can intervene in winter if necessary
  • rainy, cool spring
  • rapid alternation of frost and heat (sun) in early spring

In all of these cases, the flower buds may die and not bloom.

Tip: With adequate winter protection - spruce branches or shady linen - the plants can also tolerate temperatures that are a few degrees lower than the lowest temperature applicable in the respective case.

Unusual, but conceivable: In a longer mild period in autumn and/or winter, the flower buds may open prematurely without fully developing. Of course, these buds are then no longer available at the actual flowering time.


Mistakes in care can also result in rhododendrons not flowering.

1. improper fertilization

2. excessive cutting

3. lack of winter protection

To 1: It is dangerous to fertilize with nitrogen in summer (from mid/end of July). The latter stimulates the plant to new growth in autumn. If there are early frosts at this time of year while the plant is still saping, this can cause lasting damage to the rhododendron and prevent it from flowering in the new year.

Tip: It is better to fertilize only in spring and after flowering. In order to increase the resistance of the plant to cold, it is recommended to operate with phosphate and potash fertilization. This also optimizes the formation of flower buds.

To 2: Flower buds form in late summer and early fall. If you only cut at this point or even later, you will usually also remove the new flower buds. As a result, more leaf buds develop, but no more flower buds, so that there are no flowers the next year.

To 3: If rhododendrons are not properly protected in winter, significant frost damage including root rot is possible. Typical signs of this are flower buds, which first become very thick, but then die off. If there is no other explanation for the flower buds not opening, you should check the root.

Tip: It has to be white and firm. If the root is brown and mushy instead, it is rotten. In general, the plant can then no longer be saved.

deficiency symptoms

Here are a few more points that can be the cause of the missing (or unsatisfactory) flowering.

  • maybe the supposed flower buds that you finally want to see open are actually leaf buds? In some species, the latter are surprisingly large, which increases the risk of confusion.
  • small spots on the flowers that look wet and quickly enlarge indicate bud rot Ovulinia, which occurs more frequently in wet years. The flowers quickly turn brown and wither, but remain attached to the plant.

Tip: Apply fungicides preventively just before the flower buds (should) open.

  • yellow leaves may be due to an iron or nitrogen deficiency. In such a case, the flower buds will have trouble thriving and flowering properly.

iron deficiency

  • newer leaves yellowish
  • Iron is missing as a trace element in the soil (fertilizer) - either one or the other is the case
  • pH value is too high (plant cannot absorb the iron that is actually present)*

nitrogen deficiency

  • older leaves yellowish
  • Inappropriate fertilization


Not every rhododendron has dark green leaves. Some species tend towards lighter, yellowish nuanced versions. So you can't just infer B from A.

lack of buds

Poor flower bud formation

Isn't the problem just that buds just don't want to bloom, but also that they aren't formed properly? Then the following causes come into consideration.

  • too much shade - the more sun, the more flower buds - but too much sun carries the risk of sunburn and dehydration - dominant shade encourages foliage rather than flower bud production
  • cool, wet summer
  • too little phosphorus and potassium - phosphorus favors the formation of flower buds and a high resistance of the same - potassium strengthens the shoots and supports winter hardiness
  • unbroken wilted inflorescences
  • Plants grown from seed - rhododendrons grown from seed rarely flower or do not flower until old age - they need at least one to two years longer than their relatives (rooting of cuttings)

Tip: Most rhododendron species take two to three years from rooting the cuttings to the first flowering. Only with a few exceptions is it faster (but also slower for some).

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