Citrus are native to Asia and are attractive, evergreen trees with fragrant blossoms. They are one of the most popular trees in the home garden but unfortunately unhealthy looking specimens are common, as their needs are not always understood. Citrus need regular feeding and attention paid to preventing pests and diseases.
One important rule for citrus is NEVER GROW IT IN THE MIDDLE OF LAWN, with grass right up to the trunk and expect it to thrive. The grass competes for water and nutrients and also releases allelopathic chemicals into the soil that diminish the vigour of the tree.
• In Queensland and warmer areas of NSW citrus can be planted in late winter or early spring but bare-rooted trees should only be planted in winter. In cooler areas spring is the best time for planting. Always remove any fruit on the young tree before planting, or better still select trees without fruit for more vigour.
• Choose an open, sunny position, preferably north to northeast facing, with shelter from strong winds. Wind can distort the shape of leaves with the damage becoming apparent months later.
• A fertile, well-drained soil with a pH between 6 - 8 is best. Citrus are vulnerable to root-rot so care must be taken to avoid badly drained areas. Ideally, prepare the soil several months ahead by digging over an area 1m in diameter and at least 30 cm deep. Add compost (half a barrow load), 2kg of gypsum to the m2 if the soil is heavy and 300 - 400g of lime to the m2 if the soil is acid (ph below 6.5). Mulch heavily and leave to decompose. If the drainage is poor it may be necessary to create a mound to plant on.
• When ready to plant dig the hole to twice the depth of the container and twice as wide. Add 1 kg of organic fertiliser to the bottom and work thoroughly through the soil with a fork. Then backfill the hole so that the tree will be at the same depth it was in the pot. Soak the tree, still in the container, for a couple of hours before planting, in water enriched with a small amount of seaweed fertiliser. Remove the tree from the container and gently tease out the roots so that they are not twisted together or circling. Trim off any damaged roots. Gently backfill with the soil, making sure there are no air pockets. Make sure the graft union is as high above the soil level as possible without exposing roots. Form a rim of soil about the same diameter as the container to aid in watering, so that water does not run off too fast. Give the tree a good soaking, remember to water again in a week but do not allow it to completely dry out. Mulch around the tree well, but keep the trunk free of mulch for about 10 cm.
• 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.
Article by Frances Michaels
Green Harvest Organic Gardening Supplies