Growing avocados
Setting up a profitable avocado orchard requires careful planning and the right site, land and climate.
Guidelines:
- Avocado information kit
- Register with Avocados Australia to read the Best Practice Resource.
Land and growing conditions
Soil is the most important criteria when selecting an orchard site. Avocados are very sensitive to poorly-drained conditions and are also susceptible to Phytophthora root rot which thrives in poorly-drained soils. In high rainfall areas avocados require at least 2m of well-drained soil. In areas of lower rainfall at least 1.5m of well-drained soil is recommended
It is also strongly recommended that tree rows are mounded prior to planting. Ensure that the mounds are well designed so they don't cause water to dam up but allow it to drain away quickly without causing soil erosion. There should be a fall of 2–5% along the mounds to prevent water ponding within the orchard.
Slopes of up to 15% are suitable if the orchard is already set up to minimise erosion.
Avoid steeper slopes because they are a major erosion risk and make it difficult to operate machinery safely.
Avoid windy sites to minimise abrasion of fruit and limb breakage.
Ideally, plant on slopes that face away from the direction of the main prevailing winds, and in warm areas avoid westerly slopes as they can be very hot and result in sunburnt fruit.
You may need to plant windbreaks to protect your trees.
Frost-free areas are preferred, but mature trees will tolerate temperatures as low as -4°C for short periods without damage unless flower buds, flowers or fruit are present. Trees can also tolerate temperatures as high as 40°C for short periods, however fruit damage and losses can be expected. Growers in hot areas use overhead sprinklers (assuming good quality water is available) for evaporative cooling to preserve the crop during heat waves.
For avocado trees to produce flowers, a period of about 4 weeks of relatively cool temperatures needs to occur in autumn/winter. Flowering in Hass in coastal areas north of about Yeppoon will generally not be satisfactory. For fruit set to occur, periods of 3 days in a row are needed at flowering time during which the temperature does not drop below 10°C.
Water supply
Maintain an adequate water supply to the trees throughout the year, to meet moisture requirements and for effective uptake of nutrients.
Avocado trees must have well-aerated soil. They cannot tolerate heavy or waterlogged soil, so it's important to monitor the trees and soil as part of your irrigation process.
Avocado trees that don't get enough water can experience:
- summer stress resulting in early flowering and poor fruit set
- increase of fruit shedding in spring and early summer
- reduced fruit size, particularly if stress occurs in the first 6-8 weeks after fruit set
- poor quality fruit due to reduced uptake of boron and calcium.
Too much water causes:
- reduced tree vigour as a result of reduced soil aeration
- increased incidence and severity of Phytophthora root rot
- increased leaching of nutrients from the root zone, which wastes fertiliser and poses an environmental hazard by polluting groundwater.
Water quality
Avocados are sensitive to poor-quality irrigation water. They require water that has a low conductivity value (low in soluble salts) and a low chloride content.
Ideally, water salinity should not exceed 0.6 deciSiemens/m (equivalent to 384 ppm total soluble salts) and chloride content should not exceed 80mg/L. Water with salinity and chloride levels slightly in excess of these guidelines can be managed by using more tolerant rootstocks (e.g. Velvick) and by periodically applying extra irrigation to leach (flush) salts from the root zone.
Analyse new sources of irrigation water before use, and test existing sources regularly if a change in quality is possible.
Irrigation
Irrigation is essential in most of Queensland, particularly from August to April.
For coastal areas with high rainfall, a water storage reserve of 5 megalitres per hectare (ML/ha) is generally necessary to maintain production in a dry year. This needs to be increased to about 8–12ML/ha in drier coastal areas and inland areas, such as the Central Burnett of Queensland and Mareeba in North Queensland.
Use an effective soil moisture monitoring system to help you schedule irrigation events. Devices used can include tensiometers, gypsum blocks and capacitance probes.
Using beehives to pollinate
If your orchard lacks significant bee (or other pollinator insect) activity, we recommend 2 to 10 honey bee hives per hectare of trees to help pollinate avocado flowers.
Introduce hives when about 10% of the flowers have opened. Order the required number of hives in advance.
Pruning
Without canopy management, yield and fruit quality will deteriorate and trees will become more physically difficult to spray and harvest.
The type of canopy management practice will depend on tree density and the growth habit of the variety.
The aim of canopy management is to:
- keep trees to a practical size
- allow sunlight into the canopy to encourage flowering and fruit set
- rejuvenate the branches to keep them productive.
For a spreading, multi-branched variety such as Hass, selectively remove 1 major limb per year, e.g. for a tree with 4 major limbs, no branch will ever be older than 4 years. Upright varieties, such as Gem® or Reed trees, will need to be 'topped' every 2 or 3 years to keep height down, as well as some selective pruning of side branches.
Conduct major pruning after harvesting, i.e. during autumn or winter. Pruning too early in autumn (whilst temperatures are still high) could result in counterproductive rapid regrowth, whilst pruning too late (shortly before hot days are expected in spring or early summer) could result in sunburn to newly exposed limbs and poor fruit set.
Seek specialist advice and experiment with the timing and severity of pruning to find the most appropriate practice for your orchard.