Lower levels of salts can cause the tree to grow poorly or to produce fewer or smaller fruit. Nutrients that citrus needs in relatively large amounts are nitrogen, phosphorous, potassium, sulfur and calcium. In lesser amounts, citrus requires iron, magnesium, copper, zinc, manganese, molybdenum, boron and chlorine. In California and Arizona soils, usually only nitrogen must be added, most often in late winter to meet the demands of spring bloom. Pruning Unlike most other fruit trees, citrus trees don't require regular pruning.
Hand pruning opens up the trees to allow more sunlight into the center.
Frost Control Protection from frost is critical. The main methods of frost protection in California and Arizona are by wind and water. The fans mix the slightly warmer air above the grove with the colder air near the ground, which warms the air around the tree. By applying water, the heat built up in the soil during the day is lost more slowly, and air temperatures around the fruit stay warm a little longer. A few growers still use oil-burning orchard heaters, but this once common method is seldom used now because of the cost.