Q: I live in Tucson (caliche paradise). I have a ruby red grapefruit tree in my patio. It is 20 years old, 17 feet tall. Over the years I have trimmed it into a nice shade tree that gives us 150 square feet of shade. It has four separate trunks off the main trunk. The main trunk is 38 inches in circumference. I just harvested it and counted over 500 large grapefruit. I have not fed it in the last 10 years. I deep water every 10 days in the summer and once a month in winter. What is the normal life span? What am I doing wrong?
A: Grapefruit trees do not need a lot of fertilizer. A mature tree of the size you described probably has roots extending past the patio and receiving fertilizer from your turfgrass, garden, etc. Or perhaps the site is on a former agriculture field and there is still some residual fertilizer left in the soil. Or perhaps there is fertilizer in the irrigation water. Sooner or later, the tree will show nutrient deficiencies. Maybe it already is, but your yield is not yet affected. Grapefruit trees can live to be 50 years under ideal conditions but insects, diseases, and user errors often take their toll and shorten life spans. Your irrigation schedule seems to be on track so other than finding a way to add some fertilizer to the outer root zone, I think you are doing a fine job taking care of your tree.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to
