What to do to help a sad avocado tree

Q: We have an Avocado tree that is not doing well.  It was planted last spring and is on a drip system, however it is looking “sad.” What can we do to save this tree?

A: Avocado trees are a popular choice for home gardeners who live in frost-free areas of California. One of my fellow master gardeners remarked that every time he picks an avocado, he’s saving a dollar.

When planting a new tree, choose a site that has good drainage and plenty of sun. Avoid planting in a spot that is subject to strong winds. (Another lesson we learned the hard way.) Dig a hole that is twice the diameter and not quite as deep as the nursery container – the root ball should be just about one inch above the soil level. If the tree sits below the soil level, it can be subject to rot and if it sits too high, the roots can become exposed and dry out.

Most of the avocado’s root system is within 6 inches of the soil surface, so heavy mulching is essential for keeping moisture levels constant. Apply mulch in a 3-foot radius around the trunk, but don’t allow the mulch to contact the trunk since this can encourage fungal growth.

Drip irrigation is helpful for keeping the roots evenly moist but remember to move the emitters further from the trunk as the tree (and its root system) grows. Avocados do not go dormant, so they will require regular irrigation between rainy periods during the winter months. In the hot summer months, a mature tree will need 2 inches of water per week. Watering requirements may vary depending on tree size and maturity, soil conditions, wind, temperature, and humidity. The key is to keep the root zone moist, but not soggy.

Fertilization is important for healthy growth in both young and mature fruiting trees. Apply a nitrogen-rich fertilizer (such as ammonium sulfate) in the fall or early winter. For the first year, apply 2 tablespoons of ammonium sulfate every 4 months. If your tree has been in the ground for longer than a year, but is still puny, treat it as a new transplant.

Avocados can also suffer from micronutrient deficiencies. Foliar feeding (spraying a liquid fertilizer onto the leaves) or soil application of zinc sulfate and iron sulfate can remedy this.

Finally, if the trunk is exposed to direct sun and showing signs of sun damage, paint it with white latex paint diluted 1:1 with water.

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Author: Laura Simpson

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