Why Do the Fruits Fall Off the Citrus Trees?
Whether you're growing your citrus tree for the fruit it produces or as an ornamental specimen for its form, foliage, flowers and fruit, you're likely alarmed when the citrus fruits begin to drop prematurely. Some amount of fruit drop at a certain stage of development is normal, but an excessive drop of older fruit could indicate a number of problems.
Normal Fruit Drop
Citrus trees normally drop some of their young fruits as a means to thin the fruit out and devote resources to the development of the fruits that remain. Beginning soon after blossom drop, and ending when the fruit has a diameter of about 1/2 inch, it is normal if approximately 80 to 90 percent of the fruit falls off the tree. A small amount of fruit may continue to drop as it grows on the tree.
A number of nutrient deficiencies can contribute to excessive fruit drop, and identifying the exact nutrient deficiency means you can apply the right fertilizer to correct the deficiency. A nitrogen deficiency appears first as a yellowing of older leaves, while a magnesium deficiency appears as a yellowing between veins on older leaves and leaf drop. Inadequate zinc causes young leaves to be abnormally small and have yellow blotches between veins, particularly on the south-facing side of the canopy. A citrus tree lacking manganese has leaves that turn a lighter green between leaf veins. An iron deficiency, most prevalent in alkaline soils with excessive moisture, appears as interveinal yellowing. In heavy fruiting years, low potassium levels can impact fruit drop.
Good water management is crucial to avoid excessive fruit drop and other citrus tree problems. Excessive watering, poorly drained soils or drought stress can lead to fruit drop. As a general rule, citrus trees prefer a slow, deep watering every five to 14 days during dry, hot weather, depending on the citrus tree's age, and every 14 to 30 days during cool, wet weather, or whenever the soil 6 inches below the surface near the tree feels dry to the touch.
Other Causes of Fruit Drop
Excessive pruning can stress the citrus tree and remove too much of its foliage, forcing fruit drop. A severe pest infestation can also stress the tree enough to cause fruit drop. Sudden changes in temperature, particularly when high temperatures occur at or shortly after fruit set, can cause fruit drop. Where citrus trees are planted in poorly drained or low-lying sites, fruit drop caused by brown rot can become problematic following extended periods of wet and warm weather in late summer and fall.
Angela Ryczkowski is a professional writer who has served as a greenhouse manager and certified wildland firefighter. She holds a Bachelor of Arts in urban and regional studies.