Question: I have a pomegranate bush, which produced about 30 pomegranates last year. Initially, the pomegranates seemed to be very healthy. However, as the season progressed, prior to ripening, they all began to split open. This year's crop has already started doing the same thing. Is there anything that I can do to prevent all of them from following suit? If not, perhaps you can suggest something that I can do for next season.
- V. Gonzales, Socorro, NM
Answer: My first thought was that splitting is a good sign. My dad knew his pomegranates were ripe when they split. He took great pains to grab the newly split fruit before the ants found them. One year, he even rigged a hammock over the driveway to catch ripe fruit that fell while he was at work because the split ones would explode when they hit the ground.
Splitting before the fruit ripen is a real problem, though. Over the past year, I've gotten this same question from gardeners in Bernalillo, Doña Ana, Otero, and Sierra Counties. Resources from multiple Cooperative Extension programs across the country point to consistent irrigation as the key to keeping pomegranates from splitting too early.
Pomegranates are a low-water-use tree, to be sure, but it's irrigation irregularity that is likely to be the issue. This is because the whole fruit gets bigger and bigger after bloom, but if at some point it is stressed for water, the outer peel may stop growing. Then, when watered, the seeds inside continue to expand and can rupture the leathery peel if it's too tight. This happens with other fruit as well; I'm specifically thinking of tomatoes.
Tree problems are often difficult to diagnose because the symptoms pop up long after the damage was done, so it's hard to know exactly what started it all. Having a regular irrigation schedule for your pomegranate trees can help ensure consistency and reduce early fruit split. Here are recommended guidelines for irrigating established pomegranate trees: Water the entire root zone (at canopy dripline and several feet beyond) to a depth of about 2–3 feet every 7–10 days when temperatures are getting above 90°F. When daytime temperatures are cooler, but still getting above 70°F, back off and irrigate to that same depth every 2–3 weeks. In the winter, irrigating once a month is recommended, but continue to water to the same depth and out beyond the dripline to encourage those powerful, but tiny, lateral roots. If you are like me and you accidentally wait too long between irrigations, don't try to overcompensate with extra water. Pomegranate trees that are water stressed may take up too much water too quickly once it's available, and this can instigate early fruit split.
It's always a good idea to check the soil moisture before watering to be sure you are not overwatering. During monsoon season, you may be tempted to skip an irrigation, but go out and see how deep the rain soaked in before making your decision. Conversely, if we get over a half inch of rain or so, you may very well need to adjust your schedule. Always apply water directly to the ground (preferably mulched ground). Do not spray or sprinkle water on the foliage, flowers, or fruit, because doing so practically invites pathogens, and pomegranate flowers are very sensitive to high humidity.
Splitting fruit was a challenge reported in pomegranate research trials performed by the University of Arizona. The actual cause of splitting was not determined, although it was speculated that uneven watering could have had something to do with it. Researchers noted that 1) after splitting, fruits were more likely to be further damaged by the leaf-footed plant bug and 2) younger trees had more problems with splitting fruit than older trees. They studied 32 cultivars of pomegranates planted at three different elevations: 164, 2,490, and 3,700 feet above sea level.
Conducting pomegranate cultivar trials for residential landscape use across New Mexico is a high priority for me. Pomegranate trees (Punica granatum) are native to the region that stretches from present-day Iran, Afghanistan, Pakistan, and northern India. Through the millennia, they were cultivated to grow in warmer regions of the Mediterranean. Most of the cultivars currently available at nurseries in the U.S. are from that Mediterranean lineage. Therefore, it makes sense that they perform well in California, Arizona, and southern New Mexico. Reference books I checked listed USDA Plant Hardiness Zones 7–10 or 6–8, depending on the pomegranate cultivar. Commercially available cultivars thrive in southern and central New Mexico. Potentially, by testing other cultivars from the original native range, which has much colder winters and lower precipitation than the Mediterranean cultivars, we will find a few that are well adapted for colder parts of our state. Stay tuned!
For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms (http://desertblooms.nmsu.edu/) and the NMSU Horticulture Publications page at http://aces.nmsu.edu/pubs/_h/.
Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, office: 505- 865-7340, ext. 113.