Citrus tree health and fruit production depend on proper nutrition. Fertilization is necessary to support tree vigor and maximize the yield of high-quality fruit. California’s unique climate, which lacks severe winter dormancy, means the trees have nearly continuous nutritional demands. Understanding when and how to provide these nutrients is fundamental to successful citrus cultivation.
Understanding the Citrus Growth Cycle in California
The timing of nutrient application is tied to the citrus tree’s natural growth cycle, which occurs in distinct bursts called “flushes.” Citrus trees typically experience two major flushes annually, corresponding with high nutrient demand. The most significant is the spring flush, occurring from late winter through early spring, coinciding with flowering and fruit set.
This intense biological activity requires energy and nutrients to support the development of new leaves, flowers, and fruit. A second, less vigorous flush often occurs during the summer months (May through July). These flushes are when the tree’s root activity and nutrient uptake are at their peak.
During cooler winter months, root activity slows substantially, leading to a period of semi-dormancy where nutrient uptake is minimal. Applying fertilizer when the tree is dormant is ineffective and can lead to nutrient runoff or salt buildup. Applications should be timed to precede and fuel the active growth periods.
The Optimal Annual Fertilization Schedule
The most effective fertilization strategy divides the total annual nutrient requirement into several smaller applications to align with the tree’s growth flushes. For mature, established citrus trees, a split application schedule is recommended. The first and most substantial application should occur between late January and early March, just before the spring flush and bloom.
This initial application provides the energy needed to support the heavy demands of flowering and fruit set. A second application should follow in late spring (around May) to sustain the first growth flush and prepare for summer heat. A final application is often done in early summer (around June) to support the subsequent summer leaf flush and fruit sizing.
Young, newly planted citrus trees require a modified schedule due to their underdeveloped root systems. Instead of three large doses, young trees benefit from smaller, more frequent applications, split into four to six doses from late February through August. This approach delivers a steady supply of nutrients without overwhelming the limited root zone.
Fertilization should cease by late summer, generally no later than August, allowing the tree to harden off its growth before cooler weather. Applying fertilizer into the fall stimulates tender growth highly susceptible to frost damage and can negatively affect fruit quality.
Essential Nutrients and Application Techniques
While citrus trees require a balance of many elements, the primary nutrient for California growers is Nitrogen (N), which drives vegetative growth and fruit production. Mature trees typically require about one pound of actual nitrogen per year for a standard-sized tree. This amount is then divided across the annual application schedule.
California soils are frequently deficient in certain micronutrients, notably Zinc (Zn), Iron (Fe), and Manganese (Mn). Deficiencies appear as characteristic yellowing between the veins of new leaves. These micronutrient needs are often best addressed with a foliar spray applied directly to the leaves, timed with the emergence of new growth in the spring.
When applying granular fertilizer, spread the material evenly over the soil surface, beginning a short distance from the trunk. The fertilizer should be distributed out to the tree’s drip line—the area beneath the outermost edge of the canopy. This is where the majority of the active feeder roots are located.
Fertilizer must not be piled directly against the trunk, as this can cause bark damage. Following the application of soil-based fertilizer, water the area thoroughly. Watering helps dissolve the nutrient salts and moves them into the root zone for uptake.