In the Garden:
Southwestern Deserts
September, 2011
Regional Report

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An inner berm of soil around the trunk helps prevent the spread of water-borne fungus.

Growing Healthy Citrus Trees

After a long hot summer, your citrus trees will benefit from a little TLC. Proper irrigation and fertilizing are key to growing healthy citrus. Put your trees on a regular schedule of food and water, and they will reward you with bumper crops of luscious fruit.

Watering
Apply water around and slightly beyond the tree's outer canopy edge. This is where feeder roots are actively absorbing water and nutrients. If you have an older tree that still has drip emitters or bubblers near the trunk, that water is being wasted because there are no feeder roots in that area. Move emitters and bubblers outward as the canopy grows to keep up with the expanding root zone. If you apply water with a hose, simply drag it to the canopy edge.

Keep water from standing against the bark tissue by building a doughnut berm of soil one foot out from the trunk. This helps prevent deadly phytophthora, a deadly water-borne fungus that can kill citrus trees quickly.

How often to water depends on many factors, including weather and soil type. As a general guideline in September and October, water trees that have been in the ground for one year or less every 5 to 7 days; water trees that are one to two years old every 10 days; and water trees that are three years or older every 14 to 21 days. As temperatures cool November through January, water trees of the above ages every 14 days, 14 to 21 days, and 30 days, respectively.

Apply water slowly, allowing it to soak deeply through the root zone. This also helps leach salts beyond the roots to prevent salt burn. For newly planted or young trees that have been in the ground less than two years, water should soak 18 to 24 inches deep. As trees mature, water should soak 3 feet deep. Remember to apply the same amount of water with each irrigation (sufficient water to soak the appropriate depth). It is the frequency of watering that changes through the year.

Fertilizing
Newly transplanted citrus trees do not require feeding. After they have been in the ground two years and have established roots, start a regular fertilizing program. To promote healthy growth and a good crop, divide the annual nitrogen requirement for each tree into three equal feedings. This also helps prevent overfertilizing that might burn roots. Apply one-third in January/February, another in April/May and the final third in August/September.

How much fertilizer to apply depends on the tree age and size, type of citrus (mature grapefruit trees take half as much nitrogen as other types of citrus), as well as the percentage of nitrogen in the product. University of Arizona Maricopa County Cooperative Extension makes this task easy with a handy chart that shows exactly how much product to apply, depending on the age of the tree and the amount of nitrogen in the fertilizer (which is always listed on the package). No math required! Download the chart at http://ag.arizona.edu/maricopa/garden/html/pubs/MC91.pdf.


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