Camellias are spectacular plants when in flower, and by growing a range of species and cultivars the gardener can have plants in bloom from autumn to early summer. Many of the common problems arise from growing these woodland, acid-loving plants in the wrong conditions, although they are also prone to a range of pests and diseases.
Here we give answers to many of the common problems encountered. They are grouped by the area of the shrub affected: roots, stems and branches, leaves and flowers.
Take a look at some of the common problems you might encounter on a camellia.
Sooty mould and cast aphid skins. Sooty mould is a fungus that grows on the honeydew produced by aphids and scale insects. It doesn't harm the plant but does cut out light to the leaves. Control the insect pest and then gently wipe away with a damp cloth, if required. This example also have algae growth.
Disorder: Mature camellia foliage is quite frost resistant. However, young foliage is particularly susceptible to sharp frosts in May. There is no treatment, except to cut away if unsightly. It is possible to prevent some frost damage by covering the plant with fleece when frost is forecast.
Oedema is a disorder of plants caused by the roots taking up more water than the leaves can transpire. This excess water ruptures the cells, particularly on the undersides, and leads to water-soaked patches that turn corky and unsightly. Make sure the plant isn't waterlogged or overwatered.
Insect: overwintering cushion scale nymphs. This is a sap-sucking pest. You might also see the white egg masses (see the next picture) and sooty mould (see image 1).
Pest: cushion scale egg masses. Rectangular white waxy egg masses, up to 10mm (almost ½in) long and 2-3mm (1/8in) wide, are produced by the adult scales in early summer and the remains of these egg masses persist on the foliage throughout the year
Question: My plant looks as though it is dying. I dug down to look at the roots, and found that many of them were soft and brown inside. What has happened?
Root decay in camellias can be the result of an attack by a root disease, and the main culprits are honey fungus and Phytophthora root rot for plants grown in the ground. Root decay can also be caused by waterlogging, and both soil- and container-grown plants can be affected. Phytophthora is promoted by waterlogging, and this is especially common in container grown plants where the potting media loses structure over time. Timely repotting avoids this.
Root death in container-grown plants can sometimes be the result of hard frosts – the roots can be given some protection by wrapping the container with bubble wrap.
Question: On repotting my sickly camellia, very few roots were present and there were white grubs in the compost. What are they?
Your plant has been attacked by vine weevil, which can affect a wide range of container-grown plants. The larvae feed on the roots and may also remove the bark from the stem base.
Stems and branches
Question: The branches of my camellia are dying back. What could be wrong?
Branch dieback can be another symptom of the root problems described above, as the plant struggles to take up water through its poorly-functioning root system.
The leaf blight fungi described below can also sometimes progress to cause branch dieback.
Question: The leaves of my plant have gone yellow. What has caused this?
This symptom can have many different causes. Root problems can again be responsible, but if the yellowing is confined to the areas between the veins, then the problem is most likely to be a nutrient deficiency. Being ericaceous (acid-loving) plants, camellias can suffer from iron and manganese deficiencies if the soil or growing medium is too alkaline. In gardens with alkaline soils they are best grown in containers using an ericaceous compost. Use acidic fertilisers, and avoid prolonged watering with tap water if you are in a hard water area. Chelated iron and other trace elements will allow camellia to take up nutrients in alkaline soils. Although effective chelated fertilisers are expensive and annual treatments are needed. 'Sequestrine' is a common trade name for chelated fertiliser.
Irregular yellow or creamy-white blotches on the leaves may be the result of infection by Camellia yellow mottle virus. This virus has little effect on plant vigour.
Although they are evergreen plants, camellias still periodically shed their old leaves. Don’t worry about leaves turning yellow and falling in spring or summer if this is confined to old leaves near the base and within the plant.
Question: Some of the leaves of my plant have turned brown. What is the problem?
Again, there can be a number of causes for this, such as a root problem, drought, frost damage or strong winds. Affected leaves may be shed.
If the browning takes the form of spots or blotches, then it is possible that the plant has become infected with one of the leaf blight fungi. It is sometimes possible to see small, black, fruiting bodies of the causal fungus within the affected area. In severe cases the pathogen can progress into the branch to cause dieback.
Question: Many of the leaves of my camellia have a thick, black growth on the surface. What has caused this?
The black growth is that of a sooty mould fungus. This grows on the sugary honeydew excreted by sap-sucking pests, and on camellia the usual source of the honeydew is an infestation by cushion scale. Check the underside of the leaves for small, light brown scales, often with an elongate white egg sac. Sooty mould is not directly harmful to the plant and can be washed from the leaves, but unless the pest is controlled the growth will reappear.
Question: My plant looks healthy apart from one or two leaves, which became very swollen and have now turned white. Is this a significant problem?
Your plant is affected by a fungal disease called camellia gall. Whilst unsightly, this is not a serious problem. Affected parts can be picked off, ideally before the white bloom of fungal spores is produced.
Question: The leaves of my camellia have raised corky spots and patches underneath. What has caused this?
It sounds as though the leaves could be affected by oedema. This is not a pest or disease but a physiological problem, caused when the plant takes up more water through its roots that it can lose readily through the leaves. Overwatering or waterlogging can be to blame, or occasionally camellias grown in polytunnels or under glass where humidity is high can exhibit problems of oedema.
Question: My camellia rarely flowers. Often the flower buds develop but then go brown and fall off in the spring before they open. Or sometimes flower buds fail to form at all. Why does this happen?
The buds on spring-flowering camellias, like most plants that flower at this time, start to develop in late summer of the previous year. Adverse conditions, particularly dry soil, occurring in late summer or early spring can cause the buds to abort. Ensure that your plant has an adequate supply of water during this critical time. Excessive or late feeding can also lead to bud drop – do not feed camellias later than the end of July.
Low winter temperatures can also cause the flower buds to turn brown and fall without opening – protect sensitive cultivars with horticultural fleece.
Question: The flowers on my plant opened, but most of them have rapidly gone brown. Is this frost damage?
Frost is certainly the most common cause of this symptom. The susceptibility of a plant to damage will depend on the species and cultivar, and also its position – plants receiving direct early morning sun following a frost are much more likely to be affected.
Flowers can also turn brown and fall prematurely when they are affected by a fungal disease. Possible causes are grey mould and camellia flower blight.