Last summer I received several calls about citrus care.
First, let me assure you, citrus are easy to care for. One basic "don't" and two simple "do's" and you should enjoy ample fruit next fall, and in the years to come.
Don't prune citrus.
All citrus trees have a naturally beautiful shape, forming a large glossy green globe. The plant is shading its trunk. If you prune this shape, sunlight hits the trunk of the tree, and then the trouble starts. Minor problems include fruit drop and poor fruit quality. Major problems include splitting or cracking bark, sap oozing out, gumosis, limb death, and even death of the entire tree. Avoid pruning citrus if at all possible. If you must, do so in late fall or early winter, never in summer.
That said, interior pruning to eliminate crossing branches or sucker growth needs to be done. If such pruning causes the trunk to be exposed to sunlight, paint the exposed area with "Go Natural Citrus Paint" a gray paint specifically created for the task. It can also be used on other thin barked trees such as peaches.
A well-balanced citrus fertilizer should be used. Generally this is one high in nitrate and phosphate, such as ammonium phosphate (16-20-0). Fertilizer only needs to be applied to established trees three times per year — Rodeo Weekend, Memorial Day and Labor Day. If you missed the Memorial Day fertilizer, you can do it now, but don't apply full strength. While citrus can take the heat, they are surviving the heat, not thriving in it. Full fertilizer now can put too much stress on the plant.
Apply fertilizer at least six inches away from the trunk, and extending outward to several feet beyond the branch ends. The feeder roots that take up the fertilizer are below the branch ends and further out. If your tree has a tree well and it is not that large, consider enlarging it.
Note that, at any time, too much fertilizer can harm trees as well as developing fruit. Underfertilizing merely reduces your crop yield. Ideally, water fertilizer well into the soil so it does not burn the roots. Better yet, dissolve fertilizer in water before applying. Always wait one month after planting trees to apply fertilizer, although you could apply rooting aids at the time of planting.
Citrus prefers a deep watering. Afterward, allow the soil to dry out somewhat. Soils that are watered too often result in poor fruit quality, and even problems with flowering. In moderate, loamy soils, water once a month October through March (or not at all if more than half an inch of rain falls that month). After March, increase irrigation frequency to every three weeks, and then every two or three weeks in the summer. This guide depends on soil type.
For more information on which citrus varieties to plant, the Cooperative Extension Service (626-5161) has several good citrus bulletins available. If you are really into citrus, I recommend the book published locally by Ironwood Press "Citrus," by Lance Walheim, available at most local nurseries or online from ironwoodpress.com.
Jacqueline has been writing about gardening in the Southwest for close to three decades. She is currently working on a book on growing and using the herbs of Father Kino's Mission Gardens.