Advice
RHS Help & Advice
Citrus problems
Failure to flower
Lack of light, lack of feeding, erratic watering, or low temperatures can all cause this problem.
Flowers fall before fruit sets
Dryness at the roots and lack of air humidity can cause failure to set fruit. Flowers do not need artificial pollinating.
Fruit fall
Fruits should ripen in a period of warm sunny weather, taking almost a year to develop to full size. Most cultivars set too much fruit for the size of the plant. Some of these will be shed but clusters should be thinned to one fruit each on young plants.
Leaf drop
Caused by draughts, too low or high temperatures in winter, often coupled with too much water in winter. Citrus prefer a cool winter rest. Provide lemons with a minimum winter night temperature of not less than 10C (50F) and calamondin oranges 13C (55F).
Leaf yellowing
There are several possibilities - too wet or too dry at the roots, draughts, too low temperatures, lack of feeding or red spider mite infestation.
Rotting roots
Can be caused by overwatering. Cut away damaged roots with some of the compost and repot in a smaller container. Keep the plant in a cool position, watering with care, in the hope that the plant may be able to make new root growth and recover.If in doubt as to the reason for a decline in growth and appearance, remove the plant from its pot and check the root condition. If roots are firm and healthy, then evaluate the plant's situation and surroundings. If the roots are crowded repot in spring.
Pests of citrus
Citrus can be attacked by aphids, mealybugs and spider mites, but the most common and persistent pest is soft scale, which sucks sap from the leaves and stems.
Symptoms
Soft scale (Coccus hesperidum) is a flat, oval, yellowish-brown insect, up to 3-4mm long, feeding mainly along the larger leaf veins on the underside of leaves. Citrus foliage becomes sticky, as honeydew excreted by scale insects accumulates on the upper leaf surface, and often develops sooty mould. Soft scale also attacks many other plants, including Ficus and bay.
Control
Honeydew and sooty mould can be wiped off the foliage with a soft, damp cloth. This will also remove some of the scales. Persistent infestations may need pesticide treatment.
For plants with edible fruit, use a plant oil spray (such as Vitax Organic 2 in 1 Pest and Disease Control or Scotts Bug Clear for Fruit & Veg) or fatty acids (Bayer Organic Pest Control, Greenfingers Organic Pest Spray or Doff Greenfly and Blackfly Killer). Several applications at 10-day intervals are needed to control the more vulnerable, newly-hatched scale nymphs.
Non-edible, ornamental citrus plants can be sprayed with the systemic insecticides imidacloprid (Provado Ultimate Bug Killer), acetamiprid (Scotts Bug Clear Ultra Gun), thiamethoxam (Westland Bug Attack ready to use) or thiacloprid (Provado Ultimate Bug Killer Ready To Use). These controls can also be used against aphids, mealybugs and spider mites on citrus plants where the fruits are not going to be eaten.
Citrus care
Watering: In winter, water moderately with tepid water, allowing the surface to partially dry out before watering, then water thoroughly, allowing excess moisture to drain away. In summer, water freely but do not allow the base of the pot to stand in water.
Feeding: Citrus respond to generous feeding. Use a high nitrogen liquid feed from early spring to mid-summer. Change to a balanced feed from mid-summer to late autumn/early winter. Special citrus feeds are available.
Humidity: Provide a buoyant atmosphere by standing plants on a large saucer or tray filled with damp Hortag or gravel. Mist the leaves in early morning in summer.