Growing good citrus with care

CITRUS GOODNESS: Our climate grows good citrus.

Here in Whanganui we have a climate that grows good citrus. Most citrus trees are subtropical or tropical and will tolerate temperatures to around -2°C. 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 warmer, the trees will grow and mature faster.
Lemons and mandarins are popular in Whanganui, although all the others are grown too.
Citrus trees will generally try and produce fruit from the first year, but at this stage the tree's 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 no fruit or low fruit numbers and a year of heavy fruit production.
To be grown successfully most citrus trees are grafted on to a rootstock. This plays a major part in determining the ultimate height the variety will grow, as well as having an effect on the hardiness of the tree. There are two main rootstocks used in New Zealand - 'trifoliata' and 'flying dragon'. Trifoliata is the most widely used: it is vigorous allowing the tree to grow to 4 or 5 metres in 15 years. It is also tolerant of heavy and wetter soils and creates increased frost hardiness. When grown in pots the trees tend to dwarf themselves to the size of the pots and can be successfully maintained at 1-2m and produce well for many years.
Meyer lemons and also 'bearss (Tahitian) limes' can be successfully grown on their own roots. These such plants 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, but 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 (epsom salts) or sequestrone which is a plant tonic of magnesium and iron. Where soils are lighter and sandy particularly in parts of Springvale, Gonville and Castlecliff an extra dose of sequestrone or epsom salts is recommended more frequently. In lighter soils particularly, an application of mulch around the base at the start of each summer will also benefit in conserving soil moisture and helping retain nutrients.
Pruning is only required for shaping, and plants are better left untrimmed to yield fruit. . Pruning is best in early spring before October when the borer beetle starts to lay its eggs. Any shoots from the rootstock should be removed as this will reduce vigour and subsequent fruiting potential.
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.
When growing citrus in pots and containers it is important to use a top of the line potting mix such as Natural Bark Potting Mix, and fertilise monthly or bi-monthly using a specialist citrus fertiliser that is suitable for pots and containers, such as Osmocote for Fruits & Citrus, or Yates Acticote for Citrus. The addition of Saturaid re-wetting granules each summer to established citrus growing in containers is highly recommended. It should be applied annually, and channels water to the root zone where it is needed most. It promotes even water distribution so there is less water run off and dry spots in potting mix and soils. It makes watering, rainfall and fertilisers more effective. It can also be used in the garden even in sandy, clay or compacted soils.
The most common problem with citrus is usually sooty mould, a black sticky substance on the leaves and stems. This is actually a secondary problem caused by the presence of particularly scale and other insects which while sucking the goodness from the tree secrete a sugary substance upon which the mould grows. The sugary substance is also attractive to ants. The good news is this is easily controlled with a spray of a suitable insecticide such as Yates Confidor. If you are unsure then take some sample leaves into a garden centre for advice.
As mentioned above avoid any pruning between the early spring to midsummer period to reduce the risk of attack from borer beetle. The tell-tale sign of a borer attack is sawdust piles on and around the plant from holes in the stems/trunk where the beetles are active. This can be controlled with the use of No Borer Spray Injector into the holes. They can be difficult to control so prevention is better than trying to fix later.
Some more unusual citrus to look out for;
Tangor Kiyomi; For something different try this hybrid citrus fruit - a cross between a mandarin and orange. It has large fruit like an orange, with the easy peel of a mandarin. Its very juicy, thick skinned and seedless when self pollinated.
Lemon Lemonade; A very juicy, lemon like fruit with a mild, refreshing grapefruit-like flavour. Fruit can be eaten fresh or juiced. Fruit has a very strong scent. A heavy cropper.
Orange Cara Cara; This sweet and juicy high quality orange is a sort of Washington Navel but with the potential of deep pink flesh in hotter weather. Fruits ripen from late winter and hang well on the tree.
Lemon Ponderosa; Extra large fruit of this citron-lemon hybrid are a favourite among collectors of novelty citrus. Fragrant blooms produce gigantic seedy lemons throughout the year with good lemon flavour.
Some of the favourites;
Lime Bearss; A hardier selection of Tahitian lime with small, thin skinned, deep green seedless fruit which turns lime yellow at maturity. Protect from frost. Tree habit is vigorous and spreading.
Orange Navelina; Our favourite early ripening navel orange which heavy cropping and vigorous. Deep orange rind, slightly oval shaped, sweet juicy fruit. Ripens from late winter.
Mandarin Satsuma Miho; Those big seedless, mandarins with the soft puffy easy to peel skin? Then plant a mandarin silverhill. This is an early ripening Satsuma variety that has thin skin, easy peel, sweet juicy fruit with segments that easily separate. This variety grows well in cooler areas.
Have a good week.
¦ Gareth Carter is General Manager of Springvale Garden Centre.