Citrus fruit are often described as hard to grow and they need to be grown in sheltered locations. But really it’s just common sense. Some citrus are much hardier than others and can be grown in less sheltered areas while the more tender ones should be positioned facing north where they capture a lot os sun and can be easily watered.
The another requirement for Citrus is that they need a free draining soil to prevent the fine feeding roots from rotting. Citrus roots not only have those fine feeding roots in the top layer, but also have quite long anchor roots which grow down into the subsoil. Positioning them away from your underground services is a consideration.
Another major consideration to grow successful Citrus is to place them where maximum sun is found because this will help fruit mature at a much faster rate than growing them in partial shade.
Another key is copious quantities of water placed over those fine feeding foots during those hot dry summer months, which if not done the plant will tend to roll its leaves and produce a reduced yield of fruit. To prolong the effect of moisture, mulch could be applied to a depth of 100mm, using such material as compost, organic mix, or similar. Its very important that you never disturb those fine feeding roots by hoeing or digging as this will have the effect of yellowing the leaves and general decline of the citrus tree. Apply mulch twice a year.
As for pest and diseases there are a few that have to be kept under control, making sure that they are sprayed before they become too bad. Aphids tend to effect the growing tips and this can stunt growth, but they are easily controlled by spraying with any insecticide or use an organic method like Pyrethrum, but spray them early.
Scale is also a problem on citrus appearing both on the undersides of leaves and along the stems. If the problem gets too bad black sooty mould grows on the honeydew excreta which can clog up the all important breathing holes on the tree. The scale insect sucks out all the moisture and nutrients from the plant effectively killing it. This has the effect of yellowing leaves, which drop off and general lack of growth is seen.
Affecting some Citrus is Verucosis which distorts the fruit with scabbing lesions appear on them. They should be sprayed when they appear usually from October to June with a copper-based spray.
Another major pest that affects the leaves and fruit of the citrus is the Red Mite which is a microscopic insect that tends to suck the juices out of leaves making the leaves appear light or even translucent as well as discolouring the fruit.
Most citrus are grafted onto trifoliata root stock which is more disease resistant and tends to produce a more compact tree which matures more quickly and often produces more fruit. Sometimes the rootstock grows away from a single bud below the graft union. Cut these off carefully with a knife very close to the main stem.
Citrus are heavy feeders requiring large applications of fertiliser at least twice a year in October and February of mainly Superphosphate that helps root development and Sulphate of Potash which helps fruit set and improves colour. The addition of slow release Nitrogen through Blood and Bone also will help in the making of constant healthy green growth.
Most citrus require minimal pruning, but quick growing plants like mandarins may require thinning out occasionally while others such as lemons require keeping in shape by cutting back long stems. This is usually done after harvesting the fruit as all citrus fruit on one-year-old wood.
There are many types of citrus. Often the choice of what citrus to grow is determined where you live and how much shelter and protection you have around your section. Most people choose lemons or grapefruit, but often oranges and mandarin can be grown.
Lemons - Meyer lemons are the hardiest of the citrus group, being compact, the fruit is medium sized, smooth skinned and matures in winter/spring, but lemons can usually be picked most of the year. Meyer lemons can be grown by cuttings and grow on their own roots.
Other lemons are Lisbon, Eureka, Genoa and Villa Franca, all being juicy, thinned skinned.
Grapefruit - Morrison Seedless is the most well known variety but one called Golden Special is also seedless, thinned skinned and generally grows into a nice shaped bush. The flesh is orange and it ripens from July to October. Because of its vigorous growth it is wise only to shape the bush on a regular basis.
Mandarin - has heavy crops of sweet fruit on compact bushes. It needs regular feeding and plenty of moisture. Clementine is probably the best all round variety with medium sized fruit of good flavour. Ripens late July to September.
Orange - these are the least hardy of the citrus fruits and requires a warm sheltered area and are often grown in containers in Christchurch. Like most citrus they require a good composted soil and plenty of moisture. The main varieties grown in New Zealand is Carters or Washington Navel which ripens from early August to September and Best Seedless which is a mid season variety ripening September to November while Harwood Late ripens in November to December.
Tangelo - these are a hybrid cross between Mandarin and Grapefruit and they are intermediate in character between the two. Seminole is the major variety grown in New Zealand and bears heavy crops of large, attractive, thin-skinned, flavoured fruit. They ripen in September and hold on until December.
Ugli Fruit - this is a hybrid between a grapefruit and a mandarin. It is a large thick-skinned pale orange fruit, ripening in August through to September.
Kumquat - these trees are small, dense and highly ornamental making ideal tub and container plants. They are relatively hardy and produce heavy crops of golden fruit which are eaten whole, skin and all.