Why Are My Carob Leaves Curling?

Root rot

Root rot is the most common cause of carob leaf curl and decline in UK cultivation. Carob is adapted to the thin, rocky, extremely well-drained soils of the Mediterranean basin, where summer drought is the norm. In UK conditions, wet winters, heavy composts, and over-attentive watering saturate the roots; Phytophthora and Pythium root rot fungi colonise the damaged root tissue, and the plant begins to decline. The first symptoms are yellowing and curling of the lower leaves, which progresses up the plant as the root system fails. The compost may smell sour; pulling the plant from its pot reveals brown, mushy roots.

What to do

• Remove mushy roots, dust cuts with sulphur, and repot into fresh, very free-draining compost (50% perlite or grit). Do not water for 2 weeks after repotting. In future, water only when the top 5 to 7 cm of compost is completely dry. In a UK outdoor border, plant in the most sharply drained position available, add horticultural grit generously to the planting hole, and do not water established trees at all except in the driest summers.

Scale insects

Scale insects, particularly soft scale (Coccus hesperidum) and woolly scale (Pulvinaria species), colonise carob stems and the undersides of the pinnate leaves. Soft scale appears as flat, oval, brownish bumps; woolly scale produces distinctive white, cottony, elongated egg masses along the stems and leaf midribs in spring. Both produce honeydew that drips onto lower foliage and supports black sooty mould growth. Infested leaves yellow, curl, and may drop. Scale is more problematic on container carob kept indoors than on outdoor trees.

What to do

• Scrub scale off with a toothbrush and insecticidal soap. Remove woolly scale egg masses by hand before the crawlers hatch in late spring. Treat with a horticultural oil spray to smother remaining scale and eggs. Wipe sooty mould from the leaves with a damp cloth once scale populations are reduced. Move the plant outdoors in summer, where natural predators help keep scale populations in check.

Cold damage

Carob is hardier than many Mediterranean trees but is still damaged by temperatures below -5°C. Cold causes the leaf margins to turn brown, curl, and dry; in a severe frost the entire leaf may die while remaining attached to the branch. Young plants are more susceptible than established trees. Container carob moved indoors for winter is protected from the worst cold but can suffer if placed in a cold porch or unheated greenhouse that drops below -3°C overnight.

What to do

• Bring container carob under glass (a frost-free greenhouse, conservatory, or cool porch above 0°C) before the first frosts. In the garden, protect the base of young outdoor carob with a deep mulch and wrap the stem and lower branches with horticultural fleece in forecast hard frosts. Established trees with a sheltered south-facing wall position recover from light frosts; cold-damaged leaves can be removed in spring once new growth has started.

Red spider mite

Red spider mite (Tetranychus urticae) can affect carob in warm, dry indoor conditions, particularly in summer or in a dry greenhouse. The mites produce pale stippling and bronze discolouration on the upper leaf surface and fine webbing on the undersides; affected leaves curl and may drop. Carob is less susceptible to spider mite than many greenhouse plants because it is not a humid-environment species, but in a very dry summer indoors the conditions can become sufficiently desiccating to favour mite populations.

What to do

• Move the plant outdoors in summer where fresh air and natural predators control spider mite effectively. Mist the foliage if the plant must remain indoors in dry conditions. Introduce Phytoseiulus persimilis if mites are detected. Treat with insecticidal soap if the infestation is severe.

Frequently asked questions

Why are my carob leaves curling?

Carob (Ceratonia siliqua) leaves curl most commonly in the UK because of root rot from overwatering, scale insect infestation, or cold damage. Root rot is the primary cause: carob is adapted to dry, rocky Mediterranean soils and the wet winters of the UK are its principal enemy; overwatering triggers Phytophthora root rot, which causes the pinnate leaves to yellow at the margins, curl, and drop progressively from the base upward. Scale insects colonise the stems and leaf undersides, causing yellowing, sticky honeydew, sooty mould, and leaf curl. Cold temperatures below -5°C cause leaf margins to brown, curl, and dry.

Can I grow carob in the UK?

Carob (Ceratonia siliqua) can be grown in the UK in the mildest areas as a sheltered outdoor tree, and more widely as a large container plant moved under glass for winter. Established trees are hardy to about -5 to -7°C for short periods. Container carob makes an attractive, drought-tolerant conservatory or greenhouse plant with handsome pinnate leaves. It requires full sun, perfectly drained soil or compost, and minimal watering; it is one of the most drought-tolerant trees you can grow. Carob pods can be produced on mature trees in very warm, sheltered UK locations, but fruiting requires decades of growth and consistently warm summers.

Is carob a good substitute for chocolate?

Carob (the dried and ground pods of Ceratonia siliqua) is used as a cocoa substitute in cooking and confectionery. Carob powder has a naturally sweet, slightly earthy, caramel-like flavour that resembles chocolate in some applications but is distinctly different; it lacks the bitterness of cocoa and contains no theobromine or caffeine. Carob is popular for people sensitive to caffeine or theobromine, and is not harmful to dogs (unlike chocolate). In baking, carob powder can generally be substituted for cocoa powder at the same quantity, though the flavour result will be noticeably different.

How do I care for carob in a UK container?

Container carob in the UK needs very different care from most conservatory plants. The most important rule is to avoid overwatering. Use a very free-draining compost (John Innes No. 3 mixed 50/50 with perlite or grit) in a terracotta pot with drainage holes. In summer, water only when the top 5 to 7 cm of compost is completely dry; in winter, reduce watering to once every 3 to 4 weeks or less. Move outdoors to the sunniest spot from May to October. Feed sparingly with a balanced fertiliser in spring only. Bring inside before the first frosts; a cool, bright conservatory or greenhouse above 0°C is ideal. Carob is slow-growing but very long-lived and develops attractive, gnarled character over many years.