Splitting oranges

Q: I have an orange tree that is 9 years old. The oranges look OK and are being watered by a sprinkling system. I also had the tree pruned this year and am getting more growth. They are starting to turn orange in color, but I noticed some oranges had already changed to the color orange or partially orange. Those are the ones I had to pick off the tree because they were all split in the middle with an orange on either side, except for one that was black (inside) on one side. I want to know what is causing the oranges to split in half. I do occasionally give them some extra water (especially in the summer) with a hose for about 20 minutes or so. Is there anything I can do to keep from losing all my oranges?

A: Split fruit can be caused by a variety of stressful conditions for an orange tree, including extreme fluctuations in temperature, humidity, soil moisture and fertilization. The rind splits when water and sugars are transported from the roots to the fruit and the rind is unable to expand quickly enough. If you are watering and fertilizing properly and otherwise taking good care of the tree, it is less likely you will have problems. The factors we have the most control over are fertilization and soil moisture so it is important to provide fertilizer at the right time of year and deep irrigation rather than just watering on the surface. I am afraid your sprinkler and hose method is not enough for your tree. I recommend you check to make sure your irrigation schedule is providing water down to 36 inches below ground. You can check this with a soil probe. It is best to install a drip irrigation system around the outside of the tree canopy and operating on a schedule that provides water 36 inches deep every seven to 10 days in the summer, every 10 to 21 days in the spring and fall, and every 14 to 21 days in the winter.

Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Email: plwarren@cals. arizona.edu