Citrus includes well known lemons, mandarins, oranges, tangelo, grapefruit, limes, lemonade and some lesser known fruits including limequat and tangor (cross between a mandarin and an orange).

These popular trees are both highly productive and ornamental. They can grow well in the garden or as container specimens, with sweet smelling white flowers during spring and summer and juicy fruits that add a decorative appearance during the autumn and winter months.

Here in Wanganui we have a climate that generally grows good citrus.

Most citrus trees are subtropical or tropical and will tolerate temperatures to around -2 C.

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Trees are fairly slow growing with a mature specimen taking 15-20 years to reach 4-5 metres. Where the location is sheltered from wind, and is warmer, the trees will grow and mature faster.

Citrus varieties originate from the warmer regions of Indo-China and the Middle-East however the Kumquat, Satsuma mandarin and Meyer Lemon are relatively Cold hardy.

Satsuma Mandarin (and its selections such as 'silver hill' and 'miho'), Navel Orange and Tahitian or Bears Lime all produce seedless fruit.

Citrus trees will generally try and produce fruit from the first year, but at this stage the trees ability to bring fruit to maturity is often questionable.

A good practice is to remove flowers and fruit for 2-3 years to allow a strong branch framework to establish. In subsequent years if the tree is still producing larger crops than it can sustain the removal of approximately 1/3 of the crop will ensure the tree does not get into a pattern of biennial bearing.

This is where the tree switches between a year of heavy fruit production and a year of minimal cropping.

To be grown successfully most citrus trees are grafted onto a rootstock. The main rootstock used in New Zealand Trifoliata, it is vigorous allowing the tree to grow to 4 or 5 metres. It is also tolerant of heavy and wetter soils and creates increased frost hardiness.

By trimming or growing in a pot citrus plants can be kept at 1.5-2.5m
Meyer lemons and Tahitian limes can be successfully grown on their own roots. These are particularly suited to pots and small gardens as the plant vigour is less than that of a grafted tree of the same type. They still fruit prolifically from a young age, the plants just don't grow as big.

Citrus are gross feeders and thrive in good soil with regular feeding of a specialised 'Citrus Fertiliser'. Plants which are showing yellowing of the foliage should in addition be given a top up of magnesium.

Yates liquid magnesium chelate is highly recommended, it is a product that makes nutrient readily available to the plant. Where soils are lighter and sandy particularly in parts of Springvale, Gonville & Castlecliff an extra dose of Epsom Salts is recommended on a more frequent basis. In lighter soils particularly, an application of mulch around the base of the tree at the start of each summer will also be of benefit in conserving soil moisture & helping retain nutrients.

A long hot summer when trees are well watered will result in better fruit production, followed by the cooler months which promotes the change in skin colour of the fruit from green to yellow. When the summer is cooler the crop yield, size or quality tend to suffer.

Gareth Carter is General Manager of Springvale Garden Centre.