The most popular citrus to grow are lemons and mandarins.
Most citrus trees are subtropical or tropical and will tolerate temperatures to about -2C. Trees are fairly slow growing with a mature specimen taking 15-20 years to reach 4-5m on a larger rootstock and 2-3m on dwarf rootstocks.
For a smaller garden, they can be contained and kept smaller with pruning or growing in a pot which will restrict the size. Where the location is sheltered from wind and also warmer, the trees will grow and produce more fruit faster.
Citrus trees will generally try to 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 two to three years to allow for a strong branch framework to establish.
In subsequent years, if the tree is still producing larger crops than it can sustain, the removal of about one-third 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 height the variety will grow to, as well as affecting 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 4-5m 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, Bearss (Tahitian) limes and finger limes can be successfully grown on their own roots. These 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, 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 showing yellowing of the foliage should also be given a top-up of magnesium (Tui Epsom Salts) or Yates Liquid Citrus Cure which is a plant tonic of zinc and manganese. Where soils are lighter and sandy, an extra dose 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 help conserve soil moisture and retain nutrients.
Pruning is only required for shaping and, from a fruit yield perspective, plants are better left untrimmed. Pruning is best completed 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 the tree’s 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 tends to suffer.
When growing citrus in pots and containers it is important to use a “top of the line” potting mix such as Ican Premium Potting Mix or Tui Pot Power. The use of a “cheap” potting mix will doom your efforts to failure.
Citrus are “hungry” plants and I recommend to monthly or bi-monthly use a specialist citrus fertiliser, such as Ican Fruit Food For Pots, Tui Enrich Fruit and Citrus or Yates Acticote Fruit and Citrus, that is suitable for pots and containers.
The addition of saturaid re-wetting granules each summer to established citrus growing in containers is highly recommended.
This product should be applied annually. It channels water to the root zone where it is needed most and promotes even water distribution so there is less water runoff 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 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 Mavrik mixed with Grosafe Enspray 99 to give maximum effect. If you are unsure, take some sample leaves to a garden centre for advice.
Avoid any pruning between early spring to midsummer 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 in the holes. They can be difficult to control so prevention is better than trying to fix later.
For more gardening information visit www.springvalegardencentre.co.nz
