Citrus trees are a cherished part of the Phoenix landscape, but growing them successfully requires understanding the unique challenges presented by the desert environment. The highly alkaline, high-pH soil common across the Valley locks up nutrients, making scheduled feeding necessary for tree health and fruit production. The intense heat and mild winters dictate a fertilization strategy unlike any other region. Strategic application ensures the tree receives the necessary elements while minimizing stress from the extreme climate.
Optimal Fertilization Schedule
The most effective feeding program for citrus in Phoenix involves three distinct applications tied to the tree’s biological growth phases. The first application occurs in late winter, typically late February to early March, just before the tree pushes new spring growth and flowering begins. This initial feeding provides the energy reserves needed for a strong bloom and subsequent fruit set.
The second application should take place in late spring, around May or early June, after the fruit has set. This feeding supports the developing fruit, helping it size up properly throughout the summer months. For lemons and limes, which often produce fruit year-round, a slightly heavier or more frequent schedule may be necessary compared to oranges or grapefruit.
The final feeding is recommended in early fall, around September or early October. This application helps the tree recover from summer stress and build up nutrient reserves before winter dormancy. It also prepares the buds for the following year’s spring bloom.
Essential Nutrient Requirements
Citrus trees are heavy feeders, and their nutritional needs are complicated by the desert’s alkaline soil, which often has a pH above 7.5. Nitrogen (N) is the most required nutrient, promoting vegetative growth and producing large, juicy fruit. A specialized citrus fertilizer blend with a high first number in the N-P-K ratio is the best choice for providing this bulk requirement.
The high-pH soil makes it difficult for roots to absorb certain micronutrients, even if they are present in the ground. This often results in chlorosis, a yellowing of the leaves while the veins remain green. Deficiencies in iron, zinc, and manganese are the most common causes of this chlorosis in the Phoenix area.
To combat micronutrient deficiencies, use chelated forms of iron, zinc, and manganese. Chelated nutrients are chemically protected, making them more stable and available for absorption by the roots in high-pH soil. Applying soil amendments like sulfur can also help lower the pH in the root zone over time.
Application Techniques and Watering
The location where fertilizer is applied is important, along with the timing and the nutrients themselves. The most active feeder roots are located under the canopy, extending outward to the drip line, which is the imaginary circle on the ground directly beneath the outermost branches. Fertilizer should be spread evenly across this area, avoiding the trunk entirely.
Applying fertilizer directly against the trunk can cause chemical burn and damage the sensitive bark tissue. After spreading a granular fertilizer, lightly rake it into the top inch of soil to prevent runoff or loss due to sunlight exposure. This ensures the nutrients are placed where the fine feeder roots can easily access them for uptake.
Watering must precede and follow any fertilizer application. Deeply watering the tree before applying fertilizer helps protect the roots from chemical burn by moistening the soil. A second, thorough deep watering immediately after application helps dissolve the granules and moves the nutrients down into the root zone.
Fertilizing During Extreme Heat and Winter
Successful citrus care requires knowing when not to fertilize, particularly during the intense summer and cooler winter periods. Fertilization must be suspended entirely during the peak heat of summer, generally July and August. Applying nitrogen during these months forces the tree to push out new, tender vegetative growth.
This soft, new foliage is highly susceptible to sunscald and burn from the intense daytime temperatures, which can severely stress the entire tree. Withholding fertilizer allows the tree to focus its energy on survival and maintaining its existing canopy during the most brutal months.
Similarly, fertilizing during the deepest part of the winter, typically December and January, is unproductive and potentially harmful. Cold soil temperatures slow down root activity, reducing the tree’s ability to absorb nutrients. Forcing new growth late in the season increases the risk of frost damage should a severe cold snap occur.