Lemon trees (Citrus limon) are small, fruit-bearing ornamentals that usually grow 10 to 20 feet high. The fruits are acidic, juicy and covered with a yellow rind. Usually, lemons have an oval or elliptical shape. Lemons turn yellow when they ripen, but there are some reasons the fruits may turn yellow prematurely. Yellowing lemons and foliage are indicative of a problem caused by cultivation or disease.
Plant and grow lemon trees in healthy conditions to prevent disease and promote normal ripening. Space trees at least 7 feet apart, and prune them to stay at 12 feet high and under. Lemon trees should be fertilised two or three times a year. Lemon trees should have well-drained, rich soil. Air circulation keeps the foliage wet, preventing disease and bacterial growth. Fungus may discolour fruits and foliage, and affect the overall health of the tree.
Different cultivars of lemon trees produce fruits year-round. Initially, lemons will be green or yellow-green in colour. As the fruits ripen, they will turn a rich, golden yellow colour. Citrus limon "Eureka" fruits grow in spring and summer. "Lisbon" fruits appear in the summer and fall. Both "Ponderosa" and "Meyer" fruits grow in fall and winter. Other cultivars may produce fruit throughout the year. Once fruits mature, they become yellow naturally. Fruits will mature on the tree, but they may be picked before they are fully ripe if the gardener wishes.
Planting location and conditions are very important for lemon trees. Some cultivars are negatively affected by bright direct sunlight. Partial shade will keep trees protected from sunburn. Like skin, lemon rinds may be burnt by the sun. Yellow or brownish spots may appear on fruits when they are sun-damaged. Lack of nutrients in the soil may cause fruits and foliage to turn yellow out of season. Chlorosis causes yellowing between the veins of leaves, indicating a lack of iron, magnesium or another nutrient. Fertilise the soil to provide trees with regular nutrition.
Leaves and fruits may turn yellow prematurely due to a condition ironically named citrus greening. When citrus greening occurs, one section of the tree will turn yellow. Root rot and other rotting diseases may cause foliage to turn yellow as well. Prevent disease by treating lemon trees regularly with fungicide.