Submitted to the Contra Costa Times on January 20, 2006

Q. Most of the oranges on my tree have split. Can I prevent this?

A.  It is very frustrating to have oranges split after caring for the tree all year. The fruit quickly becomes moldy and inedible once it splits. Splitting is not caused by any kind of pathogen; it is not caused by a disease or insect, but is a result of environmental or gardening practices.

If splitting occurs in the fall when the fruit is green, it is most likely caused by water moving up into the fruit more rapidly than the rind can accept. Fruit with thin rinds or that has been damaged is more likely to split under pressure. It appears that splitting occurs in response to fluctuations in temperature, water availability in the soil, humidity and perhaps fertilizer levels, or a combination of these factors.  Trees that are stressed appear to have higher levels of fruit split, and younger trees and those on dwarfing rootstocks may  more easily stressed due to their smaller root systems.

The best recommendation is to promote the health of your tree.  Make sure that irrigation levels in the fall are a consistent and adequate. Make sure that acidic mulch such as fir or cedar is maintained under the canopy of the tree to a depth of 3”. Feed your tree regularly but with frequent smaller applications of fertilizer rather than infrequent large amounts.

 Once the fruit has split remove it from the tree as soon as possible to prevent pests and diseases from becoming established. Fallen fruit can be composted if you have a hot compost pile, but do not add to worm bins since worms dislike citrus peel.