Gardening: Growing fruit trees at home

Citrus trees grow well in Whanganui's soil and climate. Photo / Supplied

I read today that Whanganui's population is now above 47,000 people and growing. We are meeting a number of new residents in the garden centre as they settle into a new property and plant a garden. Many from larger centres are very excited by our larger section sizes and temperate climate and the opportunity this gives to grow some fruit trees around the home.

A fruit worthy of mention is a feijoa called 'Sherbet'. This variety, developed in Taranaki, has two qualities that set it apart from other feijoa: exceptionally early fruiting with its fruit ripening in March as well as the fruit being of exceptional size.

This plant was first released in 2016 with very limited numbers. Following this myrtle rust was discovered in Taranaki and all the stock bushes and plants in production in the nursery developing 'Sherbet' were destroyed by MPI (Ministry of Primary Industries). The devastated owners were left with some cuttings in propagation as their mother stock to reproduce from. Not long after this it was decided that feijoa plants were not affected by myrtle rust anyway.

After focused production to rebuild production, Feijoa Sherbet has just been re-released in limited numbers with plants arriving into the garden centre late last week. If you miss out on one of these then it is recommended to order ahead for crops that will come available in 2020.

Fruit trees that are frequently chosen from the myriad of options are citrus. Citrus includes 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 productive and ornamental in value. 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 -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.

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 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 the removal of approximately 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 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 also be given a top up of magnesium. Yates Liquid Magnesium Chelate is highly recommended. It is a product that makes nutrients 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 in conserving soil moisture and helping retain nutrients.

Pruning is only required for 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 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.

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 tends 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 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 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. 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 then take some sample leaves into a garden centre for advice.

• Gareth Carter is general manager of Springvale Garden Centre