Citrus varieties such as finger limes perform well in mild and temperate climates, writes Gareth Carter.
Gareth Carter is the general manager of Springvale Garden Centre in Whanganui.
OPINION
Not only a source of food, the garden is a place of relaxation from the world.
Spring is a great time to add to or plant a home orchard.
There are a lot of summer-fruiting berries and frost-sensitive varieties available in the garden centre now. Varieties such as banana, passionfruit, avocado, tamarillo and cape gooseberry grow well in sheltered, frost-free pockets of home gardens. This year we have received some tropical fruit plants that are relatively uncommon in this part of the world – papaya, pawpaw, tropical Asian guava, cherimoya and lucuma. These will require warm, sheltered positions or even a greenhouse.
It is the ideal time to plant them because they will be established and be of some size by the time the cooler weather arrives in June.
It is also a good time to plant other fruit trees including apples, apricots, nectarines, plums, pears, peaches, plumcots and citrus. There are also nut trees, such as almonds, hazelnuts, macadamias and walnuts, that can be planted now.
Citrus perform well in mild and temperate climates and tolerate lower temperatures than the likes of bananas. Citrus includes well-known lemons, mandarins, oranges, tangelos, grapefruit, limes, lemonades, finger limes and some lesser-known fruits including limequat and tangor (a cross between a mandarin and an orange). These popular trees are both 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 fruits’ decorative appearance during the autumn and winter months.
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. Where the location is sheltered from wind and warmer, the trees will grow and mature more quickly.
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 or is at the cost of tree growth. A good practice is to remove flowers and fruit for two or three 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 4-5m over 15-20 years usually. It is also tolerant of heavy and wetter soils and creates increased frost hardiness. By trimming or growing in a pot, a citrus plant 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 because 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 showing yellowing of the foliage should, in addition, be given a top-up of magnesium. Yates liquid magnesium chelate, which makes nutrients readily available to the plant, is highly recommended. Where soils are lighter and sandy, an extra dose of epsom salts is recommended more frequently. 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 and helping retain nutrients.
Pruning is required for only shaping and plants are better left untrimmed from a fruit yield perspective. 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.
Any shoots from the rootstock should be removed because 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 promote 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 “premium” potting mix such as Tui Pot Power or Ican Premium Potting Mix and fertilise monthly or bimonthly using a specialist citrus fertiliser that is suitable for pots and containers, such as Ican Fruit Food for Pots or Yates Acticote Fruit & Citrus Tree. 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 and 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 a secondary problem caused by the presence of, in particular, 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, an organically certified spraying oil. If you are unsure, take some sample leaves to a garden centre for advice.
For more gardening information go to www.springvalegardencentre.co.nz.