Fertilising avocados

Correct nutrition is critical and fertiliser treatments should be based on the results of regular soil and leaf analysis.

In less fertile soils, soil analysis results may suggest adding lime, dolomite, phosphorus and selected trace elements before planting.

Applying fertiliser treatments

If you need to apply fertiliser or manure before planting, do so 6 months before so it's broken down and taken up by the soil before planting.

Never use nitrogen, potassium or animal manures on or just before planting. Fertilising soon after planting can burn the tender feeder roots of the young tree.

Pay attention to levels of:

• Nitrogen: encourages tree growth and canopy health, however too much will make the tree too vegetative and result in inferior fruit quality.
• Boron: important to add before flowering and required in light doses throughout the year, especially during flowering and fruit set. Seek expert advice as there is a narrow window between boron deficiency and toxicity. Apply lower rates to lighter soil textures and higher rates to heavier soil textures.
• Calcium: important for fruit quality
• Zinc: trace element that is often deficient or unavailable in Queensland soils.
• Soil pH (measured in water): about 5.5 to 6.5 is considered best but this range is likely to be impractical to reach in calcareous soils. Trees can grow successfully in pHs of up to about 7.5, although iron chlorosis can be an issue.

Lime or dolomite

Lime or dolomite is only necessary about once every 2–3 years and the need to use it depends on your soil analysis results. If more than 2t/ha of lime or dolomite is needed, it is best to split the application into no more than 2t/ha at a time, with 6 to 12 months between applications to avoid trace element tie ups.

Foliar fertiliser

Foliar nutrient sprays aren't generally recommended for avocados. The one exception is a foliar spray of boron at flowering where leaf boron levels are below 30ppm.

Soil and leaf analysis

Buy leaf and soil sampling kits from your local fertiliser agent and follow the sampling directions. Your local fertiliser agent may take the samples for you as part of their leaf and soil analysis service.

Leaf analysis - Sample the most recently hardened leaf flush from branches without fruit. The correct time for leaf analysis is when the summer flush has hardened off (generally April-May in Queensland). A follow-up sample can be taken when the spring flush has hardened off (about December).

Soil analysis can be done at any time, but we recommend soil samples be taken at the same time as the leaf samples so the results can be interpreted together.

Published leaf nutrient guidelines are based on analysis of leaf tissue. Sample each variety or block of trees separately and avoid mixing leaves from trees of different ages.