Gardening: Citrus trees grow well in Whanganui climate - Gareth Carter

Lemon Meyer grows well in a pot.

OPINION

Autumn is a great time of year to plant citrus fruit.

The new plants from the nurseries are lush and full because of good summer growth and garden soil is moist from autumn rains and, with winter approaching, there are high prospects of further moisture to aid root establishment.

Citrus are one of the favourite fruit plants in Whanganui, for small and large gardens as well as container production with eventual tree size being controlled by the use of dwarfing rootstocks.

The most popular citrus grown in Whanganui are lemons and mandarins, though all the others are grown too. In Whanganui we have a climate that grows good citrus.

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 4-5 metres on a larger rootstock and two to three years 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 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 a strong branch framework to establish. In subsequent years, if the tree is still producing larger crops than it can sustain, removing 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 no 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 it will grow to, 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 4-5m in 15 years. It is 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 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 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 “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 fertilising monthly or bi-monthly using a specialist citrus fertiliser that is suitable for pots and containers such as Ican Fruit Food For Pots, Tui Enrich Fruit & Citrus or Yates Acticote Fruit & Citrus.

The addition of saturaid re-wetting granules each summer to established citrus growing in containers is highly recommended. This product, which channels water to the root zone where it is needed most, should be applied annually. It 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 sooty mould, a black sticky substance on the leaves and stems. This is actually a secondary problem caused by the presence of scale, in particular, 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 the early spring to midsummer period to reduce the risk of attack from borer beetle. 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 by putting No Borer Spray Injector into the holes. They can be difficult to control so prevention is better than trying to fix later.

Less common citrus

Finger limes: These are very different to other citrus fruit. The limes are about 1cm wide and 4-7cm long - similar to a little finger in shape and size. The inside of the fruit is like small beads resembling caviar. Added to salads, sushi, guacamole, gin and tonic, and other dishes, they add zesty flavour. Finger limes come in different colours including green, yellow, brown and purple skins. The fruit ripens during summer, generally from January to April. The incredibly spikey trees can take up to five years to fruit and grow about 3m high. They are highly sought-after with trees usually selling out quickly. There are limited numbers around stores at the moment.

Blood oranges: Produces fruit with blood-coloured flesh when days are hot and nights are cold. Fruits from late winter with the colour deepening as the season progresses.

Tangor Kiyomi: For something different, try this hybrid citrus fruit – it’s a cross between a mandarin and an orange. It has large fruit like an orange, with the easy peel of a mandarin. It is 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.

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.

Kumquat Meiwa: Round, spicy, sweet fruit that is excellent for marmalade, preserves and candied fruit. A showy, smaller shrub that is excellent for container growing. The hardiest of all citrus.

Bay Sweetie: New Zealand-bred mandarin hybrid with easy-peel, sweet and juicy fruit. Few or no seeds. Ripens winter to spring. High health, attractive foliage and showy, perfumed flowers. A great home garden variety. Grows to about 2.5 x 2.5m. Full sun position in well-drained soil. Tolerates light frost. Water regularly during hot, dry spells. Fertilise regularly from spring to mid-summer.

For more gardening information visit www.springvalegardencentre.co.nz.

* Gareth Carter is general manager of Springvale Garden Centre.