What you need to know to grow an avocado

Top tips on growing avocados

• create excellent drainage
• stake your tree
• protect from wind and frost
• prepare your hole and add nutrients several months before planting

Planting an avocado tree is quite straightforward as long as you have specific knowledge about site selection, soil requirements and variety. Seedlings grown from avocado pips are rarely successful. They may grow well but never produce fruit, so buy a grafted variety, suited to Melbourne conditions, and preferably a type ‘A’ that will self-fertilise. The one chosen for the community garden is a Wurtz type A which has been cultivated in ever increasing pot sizes for the last 5 years so is sturdy and ‘ready to go’.

Site selection for avocados

Good drainage is the most vital aspect of avocado planting. Any area where water may pool is not suitable as the biggest threat to avocados is root rot. Choose a sunny site. Avocados also need protection from wind and frost. For this reason, at the community garden, a curved mudbrick wall has been built to provide some shelter from the wind but more importantly to act as a heat bank to prevent frost settling on the tree. In the home garden, a brick wall is a good substitute.

Planting avocados in a depression or on a mound?

Avocados have shallow roots which need to be kept moist so this throws up a dilemma. Do you plant them in a slight depression to avoid drying out or on a mound to make sure they drain well? The answer may well depend on your capacity to water your tree. Ideally one deep water a week is enough except when establishing the tree when 2-3 times a week for the first few months is required. However the consensus is that planting on a mound is best with the top of the growing medium from the pot, raised some centimeters above the ground to allow for the root ball to sink as it settles and thereby avoiding the tree sitting in a depression. At the time of planting, insert a sturdy stake and tie the tree to it to prevent wind damage and insecure attachment in the soil. This gets rid of the wobble factor.

Soil preparation

Begin preparing your site several months before planting. Remembering that your aim is to create a mound, dig a hole deeper than the root ball and twice as wide, adding any fertiliser that will balance your soil. This may include blood and bone, zinc and boron (Banyule soils are deficient in boron) and compost. Some horticultural sand for drainage may be necessary in heavy soil to aid drainage and for roots to quickly make their way into the surrounding soil so that they anchor the tree firmly. You will of course need enough compost/soil etc in the hole and above it too so that the top of the soil in the pot remains above the surface when planted. The deeper you can prepare the hole and the higher you build the mound, the better the drainage will be*.

Mulching and watering

Mulch to a depth of 10-15cm with coarse mulch while keeping it 10cm from the tree trunk. In addition to the watering information above, note that grey or salty water is unsuitable and only tank or tap water should be used. Avocados are fussy and require clean water.

Cultivation dos and don’ts

• do give the tree plenty of space to grow
• do give small amounts of nitrogen fertiliser every 3 months when the tree is young and before it bears fruit (except in winter)
• do increase the amount of nitrogen fertiliser over the years mainly applying it in December and January with a little only in November and February
• do give the tree some organic fertiliser in late winter to improve soil texture
• do increase nitrogen fertiliser if the tree has yellowing leaves; if dark green, do nothing
• do decrease fertiliser if the tree is failing to set any or much fruit
• do not fertilise in winter
• do not dig in the vicinity of shallow roots – weed only by hand
• do paint the trunk and spray the leaves with lime-based whitewash or kaolin clay when planting to act as a sunscreen
• do plant in spring or autumn (not in summer or winter)
• do not compact the soil around the base when planting e.g. by stamping with your feet
• do not prune unless the tree is growing too wide or too tall. If so, pinch out the terminal buds
• do not plant unhealthy, diseased or root bound trees

Choosing a variety of avocado to grow

There is one species only of avocado subdivided into three races: these are the Mexican, Guatemalan and West Indian varieties, though West Indian doesn’t come from the West Indies. (Glowinski p.341). The Wurtz for the community garden is a Mexican and Guatemalan hybrid and is a type A, self-fertilising type which is compact, small and produces good quality fruit. Some type A trees are self-fertilising but all type B trees require a cross-pollinator. Haas is the most commonly grown variety in Australia (a type A) but needs an Edranol, Sharwill or Bacon to fertilise it. Glowinski lists 11 varieties that grow in Australia and their pollinators.

*At the community garden we start with the advantage that the surface is an old en-tous-cas tennis court comprising gravel, clay and coke which is designed for good drainage. The orchards are built on top of this surface which was ripped to a depth of 450mm before five layers of gypsum, green waste, organic cow manure, mountain soil and vegie mix were added, comprising a depth of 550mm and once mulched – a total depth of 1m. Using an auger, we should be able to dig a hole at least 500mm deep. We will need to rough up the surface of the hole if it becomes shiny so that young roots can penetrate into the surrounding soil. Building a mound on top of the prepared hole will complete the process.

Reference:
Glowinski, Louis, The Complete Book of Fruit Growing in Australia, 1991, Reprint 2005, Lothian
Queensland Agriculture Youtube video, How to plant an avocado tree

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Written by Robin Gale-Baker