Why Are My Oranges Splitting?

Technically, it is still summer. 

But some trees are beginning to show their hues of red and yellow on the leaves (probably due to stress).

Football season has begun and the pumpkins are brightly colored.

And backyard gardeners are noticing that their citrus trees are developing fruit. 

But for some navel orange tree owners, the promise of a juicy, winter harvest is thwarted as the young, green fruit splits open on the branches this time of year. 

This dilemma is facing many area gardeners, including one frustrated citrus fan, Teresa, who writes to the garden e-mail bag:
    "My mom has a wonderful orange tree, and the fruit is just starting to grow. However, most of them are splitting before they even get larger than a fist. What makes them do that?" 
    
    The short answer: splitting oranges are usually due to stress to the tree, usually a combination of fluctuating temperatures, humidity, soil moisture and possibly fertilizer levels.

    The long answer, from Pam Geisel, a UC Cooperative Extension Farm Advisor, who has studied the problem of citrus split: When hot weather is combined with high winds, navel orange trees become drought stressed and begin to take water from the young fruit, causing the fruit to soften and the leaves to cup. If the tree is then irrigated heavily, the dehydrated fruit swell, causing them to crack. Young trees or dwarf varieties with relatively small or shallow root systems, as well as trees grown in very sandy or porous soils that do not retain moisture well may be more susceptible to fruit splitting.
    Backyard gardeners can help minimize fruit split in navel oranges by paying attention to the summertime weather forecasts. When hot winds are predicted, irrigate before the winds begin. After the hot winds subside, irrigate lightly for a few days and then resume a normal irrigation schedule. 
Geisel also advises: "Instead of a single large application of quick release fertilizer each year, smaller monthly applications throughout the growing season (Feb. through May) may help keep nutrient levels constant."

Citrus grower Lance Walheim, author of the book, "Citrus", says that a good watering pattern for oranges includes adjusting it to the weather. Allow the top three or four inches to dry before irrigating deeply. He explains that too much water retards the spread of roots and promotes soil-borne diseases. An orange tree that gets too little water will grow poorly and may die. Keep an eye out for the signs of moisture stress on the orange trees: wilting or off-colored foliage.

    Ask a dozen citrus growers how they fertilize, and you may get 12 different answers. The University of California has several recommendations: "Apply one application of nitrogen (ammonium nitrate, ammonium sulfate, or urea) in late December to February. Alternatively, fertilizers can be applied in several applications. Many commercial growers apply 1/3 of the total nitrogen needed in February, July, and September. Using a balanced citrus food may help to correct mineral deficiencies as well as provide a more complete nutrition. Manure should be applied in the fall so that the winter rains can leach the salts. Steer and chicken manure should be used sparingly because they are high in salt and may burn the trees. Mature citrus trees use 1-1.5 lb. of actual nitrogen (N) per tree per year."

I'm no fan of quick release, ammonia-based products; it's too easy to apply too much, and could damage your tree. Others have weighed in on why these salt-containing formulations are bad for your garden. But for those of you that can't resist those $3 bags of Sulfate of Ammonia piled up outside the drug store, remember that Sulfate of Ammonia (20-0-0) consists of 20% actual nitrogen. So, applying one pound of actual nitrogen over three feedings per year per mature citrus tree equals about a pound and a half of ammonium sulfate per application, spread evenly beneath the outer dripline of the tree, following the label directions.

     My citrus feeding regimen for my containerized (half-barrels) citrus trees is organic, applied every other week during the growing season (February through September): a combination of water soluble fish emulsion and sea kelp. Fertilizer leaches through containerized plants more quickly than in-ground plants. So, a light feeding, but more often (every other week instead of monthly), mitigates that loss.

There are plenty of complete and balanced organic fertilizers available for fruit trees, some that only need to be applied a few times a year.

Timed-release synthetic fertilizers offer the convenience of supplying  nutrients at an even rate, but are usually more expensive. 

Whichever fertilizer you choose, apply it according to the label directions. 

     Lance Walheim also advises against fertilizing oranges after the end of summer. Late applications of fertilizer to deficient trees, he says, can lower fruit quality, make  the rind tougher and exposes new growth to the ill effects of a winter freeze.
    There are no pests or diseases that cause splitting, nor is there a chemical control for it, explains Pam Geisel. It is a problem that stems from environmental or cultural conditions. Blame the weather this year. Next year, water and fertilize that navel orange tree correctly to help minimize the fruit split.