Answer: Yellowing leaves indicate lack of fertilizer or poor drainage.
Citrus trees feed heavily on nitrogen. Your fertilizer should have more nitrogen (N) than phosphorous (P) or potassium (K). Use at least a 2-1-1 ratio. Miracid Soil Acidifier is a water-soluble product that works well and is a 3-1-1 ratio. In some regions, you may be able to find specialized citrus/avocado fertilizers. Buy a good brand and apply according to package directions.
Also important are trace minerals like iron, zinc, and manganese, so make sure those are included as well. Many all-purpose products will work. We prefer slow release fertilizers in the granular form rather than fertilizer stakes. Follow rates on the package carefully as fertilizers come in different strengths, release rates, and application schedules. We recommend that you fertilize more often than recommended with most slow release fertilizers. Foliar applications of trace minerals in the form of kelp or other soluble fertilizers can be effective on leaves when half their mature size.
Container trees also will need some supplemental fertilizer. Use an organic, evenly balanced fertilizer in spring and early summer; you don't need to fertilize in winter.
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