Yellow leaves on a lemon tree signal a disruption in the plant’s ability to produce chlorophyll. This condition, known as chlorosis, indicates the tree is experiencing stress, often stemming from nutrient deficiencies, poor watering, or adverse environmental conditions. Lemon trees are sensitive to imbalances and require consistent attention to maintain their dark green foliage. Successfully treating the yellowing requires observing the precise pattern of discoloration, as the location and form of the chlorosis provide distinct clues about the root cause.
Diagnosing the Type of Yellowing
Determining the cause of yellow leaves starts by observing where the discoloration appears and the pattern it forms. Nutrient deficiencies are categorized based on whether the element is mobile or immobile within the plant, which dictates if older or newer leaves are affected first. Yellowing that starts on the oldest, most mature leaves, often toward the interior of the tree, points to a lack of a mobile nutrient, such as nitrogen or magnesium.
Nitrogen deficiency is characterized by a uniform, pale yellow coloring across the entire surface of the older leaves. Because nitrogen is mobile, the tree pulls this nutrient from older foliage to support new growth. Magnesium deficiency presents a more distinct pattern on older leaves, beginning as a yellowish-green blotch near the base. This discoloration eventually forms a characteristic inverted V-shape where green pigment remains intact around the midrib.
When yellowing manifests on the newest growth at the tips of branches, the issue is likely an immobile nutrient deficiency, most commonly iron or zinc. Iron deficiency, known as iron chlorosis, is recognized by a clear interveinal pattern where the leaf turns yellow, but the small veins remain distinctly green. In severe cases, the youngest leaves can appear nearly white, while the rest of the tree remains green.
Zinc deficiency shows similar interveinal chlorosis on new leaves, but the pattern is often less uniform, appearing as small, blotchy yellow areas between the green veins. A widespread, general yellowing affecting the entire tree uniformly often signals a severe environmental problem, such as chronic waterlogging, root stress, or high soil pH preventing nutrient uptake. Yellowing combined with leaf tip or margin burn suggests a buildup of soluble salts, indicating a need for deep, flushing irrigation.
Treating Specific Nutrient Deficiencies
For a nitrogen deficiency, the tree requires a high-nitrogen fertilizer blend, often formulated specifically for citrus, to replenish its reserves. These fertilizers should be applied regularly throughout the growing season, as nitrogen is rapidly leached from the soil, especially in container-grown trees. Using a controlled-release granular fertilizer ensures a constant, steady supply of nitrogen, which promotes vigorous, dark-green new growth without the risk of burning the roots.
Treating iron deficiency is complex, particularly in alkaline soils where iron may be present but chemically unavailable. Standard iron sulfate is often ineffective under these conditions. The solution requires using a chelated iron product, such as iron EDDHA, which remains soluble even at high pH levels. This chelated iron can be applied as a soil drench around the root zone or sprayed directly onto the chlorotic leaves as a foliar application for the quickest visual results.
Magnesium deficiency is easily corrected using Epsom salts (magnesium sulfate). A common application method is dissolving approximately two tablespoons of Epsom salts per gallon of water and applying it as a soil drench around the tree’s drip line. For deficiencies of minor elements like zinc, a foliar spray is the most effective treatment. The leaves absorb these micronutrients directly, providing an immediate boost, whereas soil applications can be quickly locked up by high soil pH.
Correcting Environmental and Cultural Factors
Overwatering is frequently the most common non-nutrient cause of yellowing. Saturated soil deprives the roots of oxygen, leading to root rot and an inability to take up nutrients. The proper technique involves watering deeply but allowing the top inch or two of soil to dry out completely before watering again, which can be verified by sticking a finger into the soil.
Soil pH plays a powerful role in nutrient availability, as lemon trees thrive in a slightly acidic range of pH 5.5 to 6.5. When the soil becomes alkaline (pH 7.0 and above), micronutrients like iron and zinc become chemically bound to soil particles, making them inaccessible to the roots. To lower the soil pH, elemental sulfur can be incorporated into the soil, which slowly acidifies the root environment over time, freeing up locked-out nutrients.
Temperature stress also impacts a lemon tree’s ability to maintain green foliage, especially during cold periods. When temperatures drop, root activity slows significantly, reducing the uptake of water and nutrients, which causes leaves to yellow and drop. Potted lemon trees should be moved to a protected location during cold snaps, and all trees should be sheltered from cold winds to minimize this temporary chlorosis.