Citrus trees thrive on constant moisture, so apply enough water slowly and deeply to thoroughly soak the root mass. How often to water depends on your soil characteristics, rainfall and weather. Use a soil probe to help determine how often to apply water (such as a pointed stick or metal rod), and poke it into the soil. It will move easily through moist soil and stop at dry soil. As trees mature, be sure to water out to their canopy or drip line, where new roots are growing. To keep water from evaporating too quickly, mulch over the root area. This will also help suppress weeds.
Citrus are also heavy “feeders.” Apply fertilizer three times per year, using one-third of their total annual nitrogen requirements. Apply in Jan/Feb, April/May and Aug/Sept. The amount to apply depends on their age and size. Follow package instructions and water thoroughly before and after fertilizing.