Citrus trees are very hungry feeders with high requirements for trace elements. A regular spray with a seaweed fertiliser such as Natrakelp will supply trace elements. Fertilise citrus trees in April/May; always water the tree well after fertilising. Never place fertiliser close to the trunk or in heaps, spread it as evenly as possible to just past the drip-line of the tree. Compost or animal manures can be used starting with about 4 kg for a 1-year-old tree to 20 kg for a mature 8-year-old tree. In November/December apply lime or dolomite if necessary to correct the pH.
Blood and bone contains mainly nitrogen and phosphorus, boost it into a more ‘complete’ fertiliser by adding a ¼ cup of sulphate of potash to every kilo of blood and bone.
Citrus need regular watering from flower bud formation through to fruit set to retain a good crop.
As they are relatively shallow-rooted, trees need even moisture throughout their root zone, water in the early morning or at night, especially during summer.
Grass and weeds compete with your tree for water and nutrients, if left to grow long and rank under the tree they also encourage Collar Rot. Wet newspaper, at least 10 sheets thick, can be used to kill weeds and grass under the tree and then topped with mulch regularly to prevent weeds returning. Always mulch past the drip-line of the tree as this is the area where most of the feeder roots are found.
Prune in June or July before the spring bud burst in frost-free areas. In frost affected areas delay pruning until after the last frost. Remove dead or damaged branches, branches growing inwards and very low branches to improve air circulation. After pruning, the lower edge of the canopy should be 60-90 cm clear of the ground. Always remove shoots from below the graft as soon as possible, as they steal vigour from the tree and if left too long, leave large wounds for disease to enter when they are cut.
Aim to have mature trees no more than 2.5 to 3 m high. Higher than this just creates problems with harvesting and pest control. Larger trees are not more productive than smaller, well-managed trees. Shape the tree after harvest in early spring.
Only ever pick dry fruit. Lemons and limes should be picked 2 weeks before required as they become much easier to juice after this time. Use secateurs to cut citrus from the tree and trim close to the ‘button’ as leaving a sharp stalk causes damage to the skins of nearby fruit in storage, causing rot. If it is desirable to store lemons for long periods they should be picked just as they are turning yellow, wrapped loosely in paper and stored in an open cardboard box in a cool, dark, well-aired place.
ORGANIC PEST CONTROL
Practice good hygiene in orchard and never leave fruit to rot on the ground.
Bronze orange bug give away their presence by their foul smell. The young pale green nymphs appear in winter, their colour changes through orange to bronze as they grow to adults. They can be serious pests in some areas, causing flower and fruit drop by sucking on the stalks. Hand removal is possible, use a bucket of hot water to knock the bugs into. Wear protective goggles, long sleeves and gloves as the caustic fluid squirted by these bugs is very dangerous and painful, particularly to the eyes.
The adult spined citrus bug has projecting horns on either side of its head, the young change colour from yellow through orange and finally to green. They attack the fruit, causing shedding of the young fruit and dry patches in mature fruit. Control by hand picking.
Collar Rot is a soil fungus that attacks the tree trunk at ground level and if left untreated can kill the tree. The first signs of Collar Rot are splitting, oozing bark and yellowing foliage. Cutting the bark back with a sharp knife or chisel until undamaged bark is reached is the main treatment. Avoid wetting the trunk when watering and take steps to improve air circulation and soil drainage.
Check for the characteristic lumps or galls of Citrus Gall Wasp on lemons and grapefruits on young branches and twigs in late winter. Prune off any affected twigs before August and burn. If there are tiny holes in the gall, then it is too late.
Scab is a fungal disease that affects young fruit particularly lemons, causing raised light brown corky scabs on the fruit surface. Good hygiene and improving air circulation will help. More information on fungal disease
Citrus Leaf Miner causes ugly distorted leaves with silvery trails in the leaf tissue, especially in spring and summer. Pest Oil is a non-toxic control, spray when new growth is about 1 cm long and reapply every 2-3 weeks.
Scale are sap-sucking insects with small, round shells and are often found along the veins of leaves and the stems of plants. They look like small bumps and can be mistaken for part of the plant, as adults do not move. Eggs are laid under the scale shell and immature ‘crawlers’ emerge. Crawlers can be moved around by wind, by ants, or by hitching a ride on a bird’s leg. Scale in large numbers cause leaf yellowing, leaf drop and dieback of twigs and limbs. In very large numbers red scale(pictured) or white louse scale can seriously damage or kill young citrus trees. To control white louse scale, spray with Lime Sulphur in winter, other scale outbreaks can be controlled with Pest Oil, which works by smothering the scale. Some soft scales, including white wax scale and black scale, secrete large amounts of ‘honeydew’, which causes problems by sticking to the lower leaves where it is fed on by a fungus called Black sooty mould. Honeydew also attracts ants, which feed on it. The ants can ‘farm’ the scale, protect them from predators. So the first step is always to control any ants, as without their protection the abundance of natural enemies in an organic garden will usually be able to keep scales under control. Keep ants out of your trees by banding the trunks with horticultural glue. Prune any low branches that are touching the ground and make sure tall stems of grass aren’t providing an alternative route for the ants. Improving the environment for the natural predators of scale is a long-term strategy that will pay off over time. Natural enemies of scale include ladybeetles, lacewings, spiders and tiny parasitoid wasps. Many beneficial insects that feed on garden pests need nectar and pollen for food during part of their lifecycle. Growing a year-round supply of suitable flowers such as Good Bug Mix will maintain beneficial insect populations throughout the year. Small insect-eating birds are also helpful in controlling scale; attract them by providing safe nest sites and a constant supply of water. More information on scale
Black sooty mould is a fungus that feeds on honeydew. Honeydew is produced by a range of insects including aphid, scale, mealybug and planthopper. Sooty moulds makes a plant look unattractive and interferes with photosynthesis.
Other pests of citrus include: spider mite; mealybug; aphid; whitefly; fruit fly; snails