When your oranges are splitting

Sigh, another nice big navel orange splits. (Photos: Kathy Morrison)

It's weather-related, not a symptom of disease or pests

By Kathy Morrison

The weather was mostly to blame for the poor tomato season, disappointing legions of backyard tomato growers. Now, as we head into late fall and the beginning of citrus season, home orchard farmers also have reason to curse the weather: The navel oranges are splitting.

Both Debbie and I are seeing this in our home orange trees. My Washington navel, an established 20-year-old in-ground dwarf tree, is in the down year of a typical citrus boom-and-bust cycle. Last year we had many oranges and they were spectacularly sweet. Then the tree lost part of one side to a couple of freezes, so we didn’t expect much in the way of a crop this year, on top of the cyclical decrease. So I was pleasantly surprised to discover about a dozen large oranges forming on the sunny side of the tree.

Note to self: Try to prevent this next year.

But now four of them have split, and we could lose the rest if these temperature spikes keep up. When I lived in Fullerton a few decades ago, we saw fruit splitting fairly often on our full-size navel orange tree, but this year is the first I can remember the current tree having this problem.

Citrus splitting is not from disease or pests, as UC Cooperative Extension experts have explained. The exact cause is unknown, but often it involves a combination of weather and situational issues, such as stressed trees and hot, dry winds. (Sound familiar?) Fluctuations in soil moisture and fertilizer also can bring it on. Oranges are the most susceptible, but mandarins and tangelos apparently can split, too.

Basically the stressed tree takes moisture from the fruit, which softens. If the tree is then irrigated heavily, or gets a lot of rainfall in a short time (remember the rainstorms in late September?), the fruit swells and cracks. The thinner rind is not able to expand enough to hold the extra moisture.

If your fruit is splitting from navel to stem, pull it off the tree and discard it. It won’t ripen properly, and the exposed flesh will attract pests. Keep your fingers crossed that the rest of the oranges will be able to grow to full sweetness.

Then next year:

-- Pay attention to the National Weather Service forecasts, especially in summer and early fall, and water your orange tree a few days before hot, windy weather is expected. After the hot spell ends, irrigate lightly, then resume the regular watering schedule.
-- Spread out feeding the tree through the year. Give it small monthly feedings rather than a single large application. A slow-release organic fertilizer is preferred.