Mild Weather Causes Concern

Without a chill in the air, orchards face an altered schedule to
produce cherries and apricots
Morgan Hill – Andy Mariani wishes it would get cold already.

While most people hate the thought of scraping ice off their windshields and shivering as they wait for their car to heat up, Mariani enjoys it. 

Or, at least, he needs it. If it doesn’t get cold soon, it may be a tough year at Andy’s Orchard.

“It is mild and we’re a little concerned, particularly about deciduous fruit trees that require a certain amount of chill in order to bloom right and perform, especially cherries.”

And cherries are what Mariani’s Morgan Hill orchards are famous for. Bing, black tartarian or van, they all need hours and hours of cold weather to go dormant and get ready for the next season. And so far, this winter just hasn’t been cold enough.

Cherries need about 800 to 850 hours of temperatures below 45 degrees Fahrenheit before they begin to bloom to reach peak performance. With the blooming season just weeks away, local trees are just halfway to their goal, according to statistics compiled by the University of California, Davis.

Without enough chill hours, Mariani said, trees will bloom erratically, produce fruit of variable color and size and not hold on to the fruit as long.

“Everything affects fruit set,” Mariani said. “The whole physiology of the tree just goes wacko.”

It’s not just cherries. The region’s vaunted Blenheim apricots are in danger as well. The apricot trees at B & R Farms in Hollister are only about two-thirds of the way to the 750 chill hours they need to be at their best.

“Last year we were behind and this year we’re more behind,” said Mari Rossi, who owns B & R with her husband, Jim. “Usually, you need to get it in December and January.”

Apricot trees will begin to bloom next week. Without enough chill, every step of the process from flowering to harvest is thrown off. Pruning, irrigation and fertilization schedules all have to be altered, and with the warmer weather, the fruit will ripen early and be less flavorful.

“They should ripen about July 4, but the last two years we’ve been harvesting in June,” Rossi said. “The climate has just changed.”

Theories about climate change abound, but Mariani prefers the local explanation over global warming. Since the spring of 2001, the number of chill hours in Santa Clara and San Benito counties has fallen dramatically, in the neighborhood of 40 percent or more, and Mariani blames development.

“It’s pavement, exhaust, night lighting,” he said. “Houses give off heat. That makes it harder and harder. Locally, the prime factor is development.”

But not all is lost for the former Valley of the Heart’s Delight. Researchers around the world are getting better at assessing the conditions stone fruit trees (trees that grow fruit with pits in them) need to thrive and inventing ways to trick trees into thinking it’s cold outside, such as defoliating trees immediately after harvest.

Kitren Glozer is a researcher at Davis. She said fears about shrinking chill hours are, in this country, unique to California, and the Santa Clara Valley in particular. Even the parched San Joaquin Valley gets bone-chilling cold in the winter.

“In most of the country, they don’t need to worry about this,” Glozer said. “But there are plenty of places in the world where the lack of adequate chilling is problematic. … There are ways to get trees to be shocked into a new season without chilling.”

A lot of the research on the topic has taken place in Israel, where scientists developed a new model for measuring chill that has benefits at slightly higher temperatures, but also includes penalties for unseasonably warm days. 

Under the new chill model, a cloudy 47 degree night followed by an overcast 52 degree day counts as chill, but a clear, frosty night followed by a bright and sunny 60 degrees does not. 

The new model doesn’t set a target for the amount of chill needed to produce optimum fruit, but establishes when farmers should apply so-called rest-breaking chemicals. Under the chill portion model, the South Valley lags far behind last year’s chill, but Mariani said the model’s outlook gives him hope. 

“I think this is more accurate,” he said. “I’m not nearly as concerned as I would be because I think there’s time to get enough chill for these cherries to perform.”

Just in case, Mariani applies special fertilizer on his trees to get the buds to open more quickly and evenly at the proper time. He also grows brooks cherries, which are a little less dependent on chill.

And Glozer said that California researchers are hard at work on methods to help cherry trees cope with warmer winters. Apricots, she said, may have more to fear from foreign imports and the marketplace than a lack of chill.

“Most of the research and most of the applications are made on sweet cherries,” Glozer said. “Apricot acreage keeps shrinking so there hasn’t been any real research done, but the lessons learned for one crop can be carried over to another. You just need to work out the details.”