Citrus productive and ornamental
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 the fruit’s decorative appearance during the autumn and winter months.
Here in Whanganui we have a climate that generally grows good citrus. Most citrus trees are subtropical or tropical and will tolerate temperatures to around -2C. 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 faster.
Citrus varieties originate from the warmer regions of IndoChina 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, Miho and Miyagawa Wase), navel orange and Tahitian lime all produce seedless fruit.
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 about a 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 heavy fruit production and a year of minimal cropping.
To be grown successfully most citrus trees are grafted on to a rootstock. The main rootstock used in New Zealand is 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 with trees reaching 1.5m if left untrimmed. 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 as a product that makes nutrient readily available to the plant. Where soils are lighter and sandy, particularly in parts of Springvale, Gonville and 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.
Pruning is only required for shaping and plants are better left untrimmed from a fruit yield perspective. 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 vigour from the tree 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 “premium” potting mix such as Tui Pot Power, and fertilise monthly or bi-monthly using a specialist citrus fertiliser that is suitable for pots and containers such as osmocote for citrus. The addition of saturaid re-wetting granules to 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. 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 scale and aphids 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 Growsafe Enspray 99, this is an organically certified spraying oil.
As mentioned above, avoid any pruning between the early spring to midsummer period to reduce the risk of attack from borer beetle. If you do prune be sure to seal cuts with pruning paste. The telltale 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.
Here are some good varieties to grow here in Whanganui;
■ Mandarin Satsuma Varieties: Do you love those big seedless, mandarins with the soft puffy easy to peel skin? Then plant a mandarin satsuma variety — good ones include; Silverhill, Kawano and Miyagawa. They have easy peel, sweet juicy fruit with segments that easily separate.
■ 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.
■ 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 is also heavier cropping and more vigorous than parent Navel. Deep orange rind, slightly oval shaped, sweet juicy fruit. Ripens from late winter. Protect from hard frosts. 2.5 x 2m.
■ Tangor Kiyomi: For something different try this hybrid citrus fruit — it’s a cross between a mandarin and orange. It has large fruit like an orange, with the easy peel of a mandarin. It’s very juicy, thick skinned and seedless when self pollinated.
■ Gareth Carter is general manager of Springvale Garden Centre
Sweet NZ grapefruit grows well in the North Island and is a Whanganui favourite.