Aug 162010
 

Citrus trees offer glossy green foliage year round, with sweetly scented flowers and beautiful and edible fruit. There are few trees that are as ornamental and practical as a citrus tree. Citrus are a must for every back yard. Varieties include: Cumquats, Grapefruit, Lemons, Limes, Mandarins, Oranges, Tangelos, Pumelos and various others.

Growing Conditions

Citrus trees prefer a full sun position. They will grow well with up to half a day of sun, but will produce more foliage and less flowers and fruit with less direct sunlight. They need to be protected from frost, which damages the foliage and fruit, and from wind. Good drainage is necessary for all citrus. Soils must therefore be well drained. Planting citrus in raised beds or pots is the best option if the drainage is poor. The addition of compost to the soil may help improve the drainage. Soils should be neutral to acid in pH to successfully grow citrus. Citrus are shallow-rooted trees and thus require regular watering especially during the hot summer months. Avoid digging or planting around the base of the tree. Keep the area under the tree free of grass and mulch well. Smaller varieties of citrus are ideal grown in large pots or tubs. Try Cumquats, Myer Lemons, Tahitian and Kaffir/Makrut Limes.

Mulching

Mulch Citrus in spring to conserve moisture during the hot summer months. Be careful not to build the mulch up around the trunk of the trees, as this may cause collar rot. Remove the previous years mulch before putting a new layer down.


Feeding

At a minimum citrus should be fertilised with Fruit & Citrus Food in early September and again in early March. In addition to this, under the mulch layer, a layer of manure and compost may be spread. Some older leaves may yellow as flowering is initiated. If the trees are well fertilised, mulched and watered during summer then an autumn application of fertiliser should be all that is required to keep the leaves green in winter. Alternatively, a liquid fertiliser may be used in winter as a quick green up.

Pruning

Pruning is really only necessary to remove dead wood and to cut out branches that are rubbing against each other; or to shape the tree as desired. Citrus Gall Wasp is prevalent in this area, so prune out all galls. Remove all shoots that come from below the graft.

Watering

Citrus are not deep rooted trees and thus require regular watering. Care must be taken to ensure they have
adequate water during the hot summer months. Do not over water citrus trees.

Pests

Aphids: usually found on new growth, particularly in spring and autumn. Squash by hand or use Garlic and Chilli sprays, Pyrethrum.

Scale insects: various types of scale affect citrus trees. These will be different colours, and are usually found near the mid vein and on the stems. Again, spring and autumn are the usual seasons when these are more
prevalent. Squash by hand or spray with White Oil or Eco Oil making sure to cover the insects.

Citrus Leaf Miner: These leave silvery trails in the leaf and the leaf edges curl inwards. Control using White Oil.

Citrus Gall Wasp

Citrus gall wasps (Bruchophagus fellis) are small (3mm) shiny black wasps native to northern Australia. Adult wasps emerge in spring, often timing emergence with the onset of a flush of new growth. The wasps have a limited flying range, so, unless they are moved by the wind, they tend to re-infest the trees they emerged from. After mating, the female immediately lays her eggs into the soft new season flush.
Best practice includes:

  • Reduce the amount of soft spring flush growth by pruning (and gall removal) and fertilising in late summer or autumn instead of late winter and spring .Use a balanced fertiliser rather than a highly nitrogenous one.
  • Spraying with Overhaul – a Kaolin clay product in spring and summer
  • Placing sticky traps (see below) into the trees around spring to catch emerging wasps and prevent them mating and laying eggs into the new growth. Adult wasps don’t fly far. They can be moved good distances by wind, but will tend to re-infect the tree they emerged from. Hence traps are useful to prevent re-infection.
  • Remove galls before spring, wrap and place in your rubbish bin (NOT your greenwaste bin).
  • Where possible, get neighbours involved and protecting their trees as well.

Sooty Mold and Ants: these are secondary problems arising from another pest problem. The presence of Sooty Mold and / or Ants is usually an indication that there is a Scale or Aphid problem. The Ants and Sooty Mold feed from the sticky exudate of the Scale and Aphids. Control the Scale or Aphids and these other problems will disappear.

Mineral Deficiencies And Other Problems

Iron Deficiency
Yellowing, mainly of the newer growth, with the veins standing out in green. Apply Chelated Iron at recommended rate. The pH of the soil may be too alkaline, making the iron is inaccessible to the plant. A trace element mixture may be added to the soil, to cover various other deficiencies.


Lack of Fruit
Trees purchased with fruit on may not fruit for several years after planting. It is best to remove the developing fruit early on young trees, so that more energy is used up in root and foliage growth to establish a strong tree. Heavy crops of fruit may result in smaller sized fruit. To avoid these problems it is best to thin out heavy crops, by thinning the newly set fruit on each branch by half to two thirds. Wheeny Grapefruit tend to fruit every second year and Mandarins may produce such dense growth they fail to fruit. Other causes usually result from uneven growing conditions, over fertilising and drought or waterlogging.

Click the following links for further information on each type of citrus…

Cumquats
Grapefruit
Lemons
Mandarins
Oranges
Tangelos