Do Warmer Winters Mean Less Fruit?

Orchard photo courtesy of Devoto Orchards & Gardens
Orchard photo courtesy of Devoto Orchards & Gardens

By Brie Mazurek, CUESA (2/20/15)

Californians have been enjoying summer weather in the dead of winter, but the downside is that unseasonably warm temperatures could threaten many of our favorite foods. The state experienced its warmest winter on record last year, and according to current reports, this year could shape up to be another record breaker, compounded by a four-year drought.

California produces the vast majority of our country’s fruits and nuts, and farmers are worried because they depend on water and winter chill for their trees to produce.

The drought has been a top concern for Stan Devoto at Devoto Garden & Orchards, who grows nearly 100 heirloom varieties of apples in Sebastopol. Many of his trees are dry-farmed, meaning they receive no irrigation besides what falls from the sky and is stored in the soil. His farm has received about 27 inches of rain this season (compared to the usual 40 to 50).

Right now, though, Stan is more concerned about the lack of cold than he is about the drought. “We don’t anticipate a good crop this year unless we start getting some really cold temperatures,” he says. “During winter we sometimes get down into the mid to low twenties, but this year there’s been no frost on the roofs, no frost on the grass. It’s scary.”

The Big Sleep

Winter chill is a vital part of the annual cycle of most fruit trees, including stone fruit (cherries, apricots, plums, and the like), pome fruit (such as apples and pears), and nuts. To bear fruit each year, the trees must undergo a period of winter dormancy, when the tree essentially goes to sleep, dropping its leaves and slowing its metabolism to conserve energy and protect itself from the cold.

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These temperate trees need a certain number of chill hours below 45ºF, with some varieties requiring upwards of 1,000 hours. (Citrus trees don’t have chill requirements and can actually be damaged in freezing temperatures.)

When the days get longer and warmer in the spring, the trees break dormancy and regain their ability to blossom, a process known as vernalization. However, when a tree doesn’t get enough chill hours, that natural cycle is disrupted, which can lead to erratic bloom, delayed pollination, and reduction in fruit yields and quality.

“Normally our trees are completely dormant by about December 1, but this year they went on into Christmas,” says Stan. “Some trees had leaves on them into February.” And some trees are starting to flower early, a process that typically takes place in late March to early April. This could pose problems if much-needed rains come in the next couple months, since warm, wet weather can lead to mildew and scab on newly forming buds, preventing fruit from setting properly.

A Warmer Normal

Chill hour chart from UC Davis.
Chill hour chart from UC Davis.

Along with many other growers, Frog Hollow Farm in Brentwood lost the majority of their cherry crop last year—90%, according to Farmer Al Courchesne—due to the warm winter. Based on the current lack of cold this season, he forecasts that this year’s crop will be the same.

With some of the highest chill requirements for stone fruit, cherries may be the canary in the coal mine, according to the California Agriculture & Climate Network, which noted that cherry harvests were down 63% in California from 2013 to 2014.

“In California agriculture, I think we’re beginning to see climate change taking place before our eyes,” says Al. “It’s the big unknown that’s looming over everybody’s crops and future.”

According to one study published in the peer-reviewed journal PLOS ONE, chill hours have decreased up to 30% in some parts of the Central Valley from 1950 to 2000, with predictions suggesting that they may decrease by as much as 80% relative to 1950 by the end of the 21st century. If those projections prove true, the report concludes, “For some crops, production might no longer be possible.” According to climate scientists, certain types of agriculture may eventually have to migrate north.

“We’ll be planting bananas, coffee, and avocados here,” Al jests dryly. “With this new warming, our climate is going to be totally different. We might be growing tropical fruits instead of temperate zone fruits someday.”

Adapting for the Future

As one strategy, some fruit farmers are transitioning their orchards to trees with reduced chilling requirements, while breeders are starting to develop new cultivars in response to the demand. But keeping pace with the Mother Nature isn’t cheap or easy.

A few years back, Frog Hollow replaced 900 unproductive high-chill Orange Red apricot trees by grafting on lower-chill varieties like Golden Sweet, Apache, and Cot-N-Candy—a move that cost the farm thousands of dollars. “Then we then had to wait two to three years for those trees to reestablish, so we lost about 10 years of production on that orchard. That’s huge,” says Al.

While farmers are well accustomed to responding to the unpredictability of nature, adapting to an uncertain climate future is a whole other story. “California has had droughts before, but this one is so long and so severe that it’s beginning to feel like this new weather pattern is the result of some new influence,” says Al.

In the meantime, he is hoping to reduce his farm’s carbon footprint by recycling farm waste, creating compost, and rebuilding their soil biologically. “All the reports I’ve read are indicating that soil building and carbon sequestration could be the brightest hope for getting us out of the climate change spiral we’re in.”

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Support Devoto Orchards and Frog Hollow Farm at the Ferry Plaza Farmers Market on Saturdays.

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