Are Your Rhododendron Leaves Wilting And Drooping? Horticulturists Explain Why
Elizabeth is a Permaculture Garden Designer, Sustainability Consultant and Professional Writer, working as an advocate for positive change. She graduated from the University of St. Andrews with an MA in English and Philosophy and obtained a Diploma in Applied Permaculture Design from the Permaculture Association.
Reviewed By PETER LICKORISH
Peter is a Horticulture Lecturer and self-employed Horticulturist, with a passion for diverse areas of the industry - from garden design to the science behind plant growth and propagation. He has completed the Royal Horticultural Society’s Master of Horticulture (MHort) Award and lectures on RHS courses at Bedford College.
Contributions From KATRINA CLOW
Katrina Clow is the Hon. Secretary of The Scottish Rhododendron Society. Katrina has over 60 years of gardening experience and has a particular passion for growing rhododendrons in her woodland garden in West Scotland.
IN THIS GUIDE
Rhododendron are typically easy to care for and low maintenance, but there are a range of issues that can cause leaves to start wilting and drooping.
In this article, we will explore some of the most common issues which can cause rhododendron leaves to wilt and droop.
“In addition to producing every possible flower colour, many rhododendrons are fragrant and have beautiful foliage,” says Katrina Clow, Hon. Secretary of The Scottish Rhododendron Society.
“They can become trees or remain diminutive little plants and so can suit many types of garden.”
1) Cold Or Windy Weather
Many rhododendron are hardy and can easily make it through the winter in the UK.
However, some cultivars may well show signs of stress in cold temperatures, especially in windy weather over the coldest months.
They will sometimes simply recover after milder conditions return.
If leaves are curling in on themselves this may just be the plant’s natural response to cold, exposed conditions, known as thermotropism.1Van Zanten, M., Ai, H., & Quint, M. (2021). Plant thermotropism: an underexplored thermal engagement and avoidance strategy. Journal of Experimental Botany. https://doi.org/10.1093/jxb/erab209
Rhododendrons curl leaves inwards so that less of the leaf surface is exposed to drying cold winds.
This is the plant’s defence mechanism to prevent too much water evaporating from the leaves.
The rhododendron may need water, if conditions have been dry, and you should make sure that you conserve that water by laying an organic mulch around the base of the plant.
“We cannot control the weather!” exclaims Katrina.
“Moist, humid and mild conditions will help prolong flower life. A late May frost or a sudden gale can destroy all the loveliness of your rhododendrons.”
Despite this, if you encounter this issue frequently, you may need to consider replacing your shrub with a more cold-hardy cultivar better suited to your location.
2) Broken Stems
If the leaves are wilting and drooping only on one side or a certain portion of the plant, the first thing to check for is broken or damaged stems.
Of course, leaves will wilt and droop if water and nutrients cannot pass up the stems to reach them.
Katrina recommends foliar feeding your rhododendrons in the growing season to make sure your plants get all the nutrients they need.
Physiological damage may have been caused not by a more pernicious issue but simply by storm damage or other extreme weather conditions – especially if your shrub is in an exposed location.
Be sure to prune out the damaged section as soon as possible to avoid putting excess strain on the rest of the plant.
But note, if water is not reaching the leaves effectively, there can be a range of other reasons for this – which we will cover below.
3) Water Shortage
Another common reason that leaves on a rhododendron will wilt and droop is issues relating to water.
In dry summer months, you may find that water shortage is the culprit.
Rhododendrons have shallow roots and require moist soil.
Make sure that you are watering sufficiently, and with sufficient frequency during dry periods.
“Spray the foliage with rainwater if required,” Katrina suggests.
Remember that smaller cultivars growing in containers will have higher water needs.
Moisture is especially critical in the middle of summer to help flower bud production for the following year. A dry summer can seriously hinder flowering.
“Large rhododendrons may be more prone to a lack of water in pots,” adds Master Horticulturist Peter Lickorish.
“If potting into something larger or planting out is not an option, they can be pruned to help them manage water.
“However, as they flower on older stems, pruning must be carried out minimally over several years to avoid a dent in blooming.”
4) Waterlogging / Excessive Watering
Wilting and drooping leaves can also unfortunately be a sign that you have watered too much.
Rhododendrons do need moist soil, as mentioned above – but they will not do well when the soil or growing medium becomes waterlogged.
During heavy rains, soils that do not drain freely may cause a problem for rhododendrons.
Make sure that you improve the soil structure with the regular application of organic mulch, which will aid in building a healthy, aerated, moisture-retentive yet free-draining soil.
If growing rhododendron in pots or containers, make sure that you have chosen an appropriate moisture-retentive yet free-draining ericaceous mix.
Make sure that the container you have chosen is allowing water to drain out the base.
5) Fungal Infection
Unfortunately, waterlogged conditions can increase the likelihood of a fungal infection taking hold, and fungal infection could also be the cause of your rhododendron leaves wilting and drooping.
Phytophthora Root Rot
One of the most common fungal infections is Phytophthora root rot.
Spores come in with plants introduced to your garden, or on the wind.
Sadly, once you see this problem in the leaves, the disease is likely to be quite advanced in the roots.
If you unearth the roots you will likely see much evidence of decay if this is the problem.
However, it may be difficult to tell whether prolonged waterlogging alone has caused this issue, or whether fungal disease is present.
Honey Fungus
Rhododendron may also suffer from honey fungus.
This is another fungus that attacks the roots of a number of woody perennial plants.
If this fungus is present, this will also cause root death before you are aware of wilting and drooping leaves.
If you look at the roots and find a white mycelium (which smells strongly of mushrooms) around the roots and the base of the shrub, this is likely to be the problem.
When one of these fungal diseases is present, you should carefully dispose of the plant and replace the topsoil from the root area.
Susceptible plants should not be grown in the same area and you should replant with more resistant species.
6) Vine Weevils Or Other Insect Pests
Vine weevils and other insect pests can also cause rhododendron leaves to wilt and droop. This can be a problem, especially, for rhododendrons which are grown in containers.
Adult vine weevils will nibble the edges of rhododendron leaves, but it is the grubs that pose a more serious problem – they feed on plant roots over the autumn and winter months, causing wilting and eventually death of the plant.
You can deal with vine weevils by picking the grubs from the compost or potting soil by hand.
This may be time-consuming but try to make sure you remove as many larvae as you can.
There are also biological controls available.
You can introduce nematodes: Heterorhabditis megidis, H. bacteriophora and Steinernema kraussei are amongst those commonly used.
These are usually applied in August or early September, but may also be applied in late spring.
If your rhododendron leaves are wilting and drooping, the problem usually relates to water.
For some reason, the leaves are not getting the water and nutrients they need.
Rule out environmental problems before deciding whether disease or pest species are causing the issue.
Working through the list above should usually give you an answer to your question.
