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desert gardening basics
February, 2014, Page 120
Lemons, tangerines and oranges (top) need to be fertilized three times a year.
Timely feedings keep trees healthy and productive
As temperatures warm and plants begin to show signs of fresh growth, it’s time to fertilize non-native plants, including citrus.
Most native trees, shrubs, wildflowers, cacti and succulents do not require supplemental feeding (unless grown in pots). Many desert trees and shrubs are legumes—plants that partner with soil bacteria to create their own form of useable nitrogen. Others have adapted over centuries to thrive with what native soil offers, and they seldom suffer nutrient deficiencies.
Non-native plants, on the other hand, evolved in different soil and growing conditions and benefit from a fertilizer boost.
Confronting the array of fertilizer products on nursery shelves can be daunting. The easiest route is to choose one formulated for a specific plant type, in this case citrus.
In addition to the macronutrients of nitrogen, phosphorus and potassium (displayed on the package as three numbers called the N-P-K ratio), these fertilizers also contain appropriate nutrients needed in smaller amounts, such as iron and manganese. Arizona’s Best Citrus Food (13-10-4) is one such product formulated for low-desert growing conditions.
Citrus trees, like most plants, need nitrogen in relatively large quantities; thus nitrogen-only products, such as ammonium sulfate (21-0-0), may be more economical than a specific fertilizer formulation, especially if you are tending multiple trees or a small orchard.
If using a product not formulated for citrus, the University of Arizona Maricopa County Cooperative Extension provides a chart that lists specific amounts of fertilizer to apply based upon tree age, size and type. Find the Fertilizing Citrus Chart at
Organic vs. Inorganic
Another fertilizer characteristic to consider is organic versus inorganic. Organic fertilizers are made from natural sources that contain carbon, such as alfalfa meal, bonemeal or fish emulsion. In addition to providing nutrients, the organic matter enhances soil structure, aeration and moisture retention, and supports earthworms and beneficial soil organisms that build healthy soil over time.
Organic fertilizers cause little to no harmful salt buildup in the soil, as do chemical (inorganic) fertilizers. However, organic fertilizers tend to be slower-acting, and they are more expensive than chemical fertilizers.
Spread fertilizer at and slightly beyond the drip line (canopy edge), where feeder roots actively absorb water and nutrients. Applying fertilizer near the trunk base of a mature tree is wasted because there are no feeder roots in that area. Instead, spread fertilizer evenly around the entire circumference and water deeply. Water should soak 2 feet deep for young trees planted less than two years and 3 feet deep for mature trees.
Fertilize citrus trees three times per year, with one-third the total annual nitrogen requirement at each feeding. Apply in January or February, April or May, and August or September. For an easy reminder, feed on Valentine’s Day, Memorial Day and Labor Day.
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