The appearance of yellow leaves, known as chlorosis, is a common symptom in citrus trees signaling a problem with nutritional intake. This discoloration is a visual cue that the tree is struggling to produce chlorophyll, the compound responsible for healthy green foliage. Chlorosis almost always indicates a deficiency in one or more required nutrients, particularly those involved in chlorophyll production. Correcting this issue requires a strategic approach: first, accurately identifying the specific deficiency based on the leaf pattern, and then applying a targeted feeding treatment.
Identifying Specific Nutrient Deficiencies
The precise pattern of yellowing is the most reliable tool for diagnosing the missing nutrient. Elements are classified as mobile or immobile, meaning deficiency symptoms manifest on either older or newer growth. Understanding this distinction is fundamental before selecting corrective feeding.
A uniform, pale green to yellow color across the entire leaf, first noticeable on older, mature leaves, signals nitrogen deficiency. Since nitrogen is mobile, the tree pulls this resource from older leaves to support new growth, causing the older foliage to become completely chlorotic. Severe deficiency may cause leaves to turn entirely yellow and drop prematurely.
Deficiencies in immobile micronutrients like iron, zinc, and manganese present differently, appearing first on the youngest, newly emerging leaves. Iron deficiency typically causes interveinal chlorosis, where the area between the leaf veins turns yellow while the veins themselves remain distinctly green.
Zinc and manganese deficiencies also appear on new growth, often causing a mottled or speckled interveinal chlorosis. Zinc deficiency frequently results in small, narrow leaves with irregular yellow banding or blotching between the green veins. Manganese deficiency presents as similar yellowish mottling, but the dark green bands along the midrib and main veins are generally more defined.
Magnesium deficiency affects older, lower leaves, but unlike nitrogen, it displays a specific pattern rather than uniform yellowing. This deficiency causes yellow blotching that begins at the leaf tips and margins, progressing inward toward the midrib. The signature symptom is an inverted ‘V’ or triangular patch of green that remains at the base of the leaf, adjacent to the stem.
General Citrus Feeding Requirements
While specific yellowing patterns require targeted intervention, citrus trees need a consistent, foundational feeding program to maintain health and prevent generalized deficiencies. Nitrogen is the most heavily utilized nutrient, driving canopy growth and fruit production. Therefore, a successful feeding regimen must prioritize nitrogen throughout the active growing season.
Most recommended citrus fertilizer blends reflect this need by having a high first number in the NPK ratio, such as 3-1-2 or 5-1-3. These ratios ensure a steady supply of nitrogen relative to phosphorus and potassium. Applying a complete fertilizer formulated specifically for citrus delivers the high nitrogen dose required for vegetative growth.
Phosphorus (P) supports root development and flower formation, while potassium (K) is required for fruit quality and plant vigor. Although both are needed, they are not consumed in the same large quantities as nitrogen, which is why a high-nitrogen ratio is preferred. The annual feeding should be split into multiple applications across the growing season to provide a continuous nutrient supply.
Specialized citrus fertilizers are beneficial over general garden products because they often include necessary micronutrients. A complete fertilizer helps ensure the tree has all the elements it needs for optimal function. This regular, balanced feeding acts as a preventative measure against nutritional problems.
Targeted Micronutrient Treatments
Once a specific deficiency is diagnosed, a targeted application of the missing element is necessary for correction. Treating micronutrient deficiencies often requires a different approach than applying granular fertilizer to the soil. This is especially true in alkaline soils where elements like iron, zinc, and manganese become chemically bound and unavailable to the roots.
For iron deficiency, the most effective treatment is the application of chelated iron products. Chelated forms are chemically protected, allowing the iron to remain soluble and available for root uptake even in high-pH soil conditions. Applying these chelates directly to the soil near the trunk provides the best long-term corrective action.
Zinc and manganese deficiencies are best treated using a foliar spray application containing the missing element. The leaves absorb these micronutrients directly, bypassing the complications of high soil pH that make them unavailable to the roots. Foliar application provides a rapid correction, making the element immediately available to the new growth.
Magnesium deficiency can often be corrected with soil amendments containing magnesium. Applying Epsom salts (magnesium sulfate) or dolomitic lime successfully supplies the missing magnesium. Epsom salts provide a fast-acting source, while dolomitic lime is suitable for longer-term correction, especially if the soil needs a slight pH adjustment.
Timing and Methods for Fertilizer Application
The effectiveness of any feeding program depends heavily on when and how the nutrients are delivered. The best time to begin the annual fertilization schedule is in late winter or early spring, just before the first flush of new growth. Subsequent applications should follow periodically throughout the spring and summer, aligning with the tree’s periods of active growth.
It is advisable to stop fertilizing by late summer or early fall to prevent stimulating new growth that could be damaged by cold weather. The tree needs time to harden off before the dormant season begins. Splitting the total annual amount of fertilizer into three or four smaller, evenly spaced doses is more effective than one large application, minimizing the risk of nutrient leaching and root burn.
Soil application of granular fertilizer should be spread evenly beneath the canopy, extending out to the drip line, but kept away from the trunk. For maximum uptake, the soil should be thoroughly watered before and immediately after applying the fertilizer to dissolve the nutrients. Foliar feeding, which involves spraying a liquid solution directly onto the leaves, is the preferred method for immediate correction of micronutrient deficiencies.