Avocado Tree Fertilization Basics

  • Apr 22, 2013

For the best consistent avocado crops, fertilizer applications should aim to keep the avocado trees very healthy. In order to produce consistent, abundant avocado crops, avocado trees need healthy leaves, they need to produce flowering wood and have strong healthy roots to take up water and minerals.

What minerals do avocado trees use? The first four listed below are the most important minerals for avocado trees.

  • Nitrogen — for growth and development
  • Potassium — for growth and fruit bearing
  • Boron — growth
  • Zinc — fruit
  • Phosphorous — healthy metabolism
  • Calcium — roots, good structure
  • Magnesium — photosynthesis
  • Sulfur
  • Iron — health
  • Manganese — health

Fertilizer applications require the right balance of minerals because the amount of each mineral in leaves, the flesh and seed of fruit, and flowers are different. Thus, some minerals are required in greater amounts than others. Very simply, avocados need the right amounts of Nitrogen and Phosphorous for healthy metabolism, Potassium and Zinc in the fruit, Calcium for good structure, Magnesium for good photosynthesis capacity, and Boron, Iron, and Manganese for good health.

Determining how much fertilizer should be used in an avocado grove

Avocado trees have a variable demand for nutrients depending on where the tree is in its cycle. To determine the exact amounts and times of applying fertilizers, monitor the avocado grove, take notes and use a specialist who will perform soil, leaf and water tests. The specialist will determine fertilizer amounts based on fruit load, cropping history, growth cycles, soil/leaf/water tests, and existing regulations. Remember — irrigation water contains nutrients as well and this must be factored into your irrigation strategy.

The specialist will determine what nutrients are needed when the following is considered:

  • Values of each mineral measured by regular soil and leaf tests including analysis of irrigation water
  • Current young and mature fruit load on the trees and the cropping history
  • Strength of the growth cycle of the tree
  • Target levels of minerals for best production
  • Regulations limiting downstream effects of fertilizer applications

Determining which avocado growth cycle is the primary sink

The nutrients needed by an avocado tree depend on the variable growth cycles and whether roots, fruit or shoot growth are the primary sinks.

  • Examine roots to see if they are the primary sink. New growth should be easily visible under the leaf litter. Look at the rest of the tree for indicators. If roots are the primary sink, there will be little shoot growth, flowering or fruit development occurring. When roots are the primary sink, apply Phytophthora control. This should generally be applied twice a year — summer and winter based on the appearance of new roots to indicate a more exact time.
  • To improve the quality of fruit provide calcium during the first 6 – 8 weeks of fruit growth.
  • Nitrogen promotes shoot growth in an avocado tree.
Event References: Fertilization Techniques, PGRs and Local Issues Updates, CAS, CAC, UCCE California Avocado Grower OUTDOOR Seminar – Field Fertilization and Herbicide Uses