Temperature changes affect stone fruit and other crops
This map shows how the average winter temperture has increased across the United States. Sacramento's winter average has increased by 2.3 degrees since 1970. Courtesy Climate Central
It’s not just your imagination: Our winters are getting warmer. And that can affect what we grow – particularly stone fruit.
According to a new report released this week by the nonprofit research group Climate Central, the greater Sacramento area is on average 2.3 degrees warmer in winter than we were in 1970.
“In our warming world, the coldest days aren’t as cold, and cold snaps are shrinking,” said the report. “Warming winters affect public health, water supplies, agriculture, and recreation.”
The report focused on meteorological winter – December, January and February. Warmer winter days mean fewer “chill hours” (time under 45 degrees) overall – vital for cherries, plums, peaches and other stone fruit to set.
“Many high-value fruit crops require a minimum number of winter chill hours,” said the report. “Warmer, shorter winters mean shorter chill periods, which could lead to lower fruit yields.”
It’s not just cold nights that are important; the trees need chilly days, too. Time spent above 70 degrees can offset the time spent under 45 degrees.
“Fruit trees and certain bushes must go through a dormant period each winter in preparation for producing fruit the following spring and summer,” explained the report. “This rest period, also known as a chilling period, is directly related to the temperature. For many varieties of trees, the most efficient temperature for chilling is 45 degrees F., with little additional chilling effect at temperatures below 32 degrees. Brief warm spells in winter have a negative effect — temperatures above 70 degrees for four or more hours offset any chilling that happened in the previous 24 to 36 hours.”
Lack of chill hours also affects apples, pears, persimmons, blueberries, blackberries, grapes, strawberries, almonds, walnuts and many perennials such as peonies. No cold, no flowers.
“One of the things we actually see in parts of Northern California impact the stone fruit,” state climatologist Dr. Michael Anderson told CBS Channel 13. “They really need those cold hours to really help produce fruit. What you start seeing is your cherry tree is only producing fruit at a certain level of the tree because that’s where the conditions are being met.”
Another visible impact: Less tule fog.
“One of the big things we don’t see so much in the Sacramento area anymore are the days of just heavy fog,” Anderson said. “As things have warmed, you get above that threshold where fog can form, all of a sudden now you’ve got clear sky, and boy, the sun can heat up the place.”
Sacramento winter is actually warming a little less than the rest of the nation, said the report, which found warmer winter temperatures in 97% of the 238 locations studied. On average, our nation warmed 3.8 degrees with the greatest change in the Northeast, upper Midwest and swaths of the Southeast.
According to Climate Central, the top-five winter warming locations were: Burlington, Vt. (7.7 degrees), Albany, Ga. (7), Chattanooga, Tenn. (6.7), Milwaukee, Wis. (6.7), and Concord, N.H. (6.6).
The report also found most of the nation is experiencing more days above normal (at least what was normal from 1991-2000, the base years used in this study). Sacramento now averages 15 winter days with high temperatures above that baseline.
The study found the cities that saw the largest increase in warmer-than-normal winter days since 1970 were: Las Vegas, Nev. (30 more days), Honolulu, Hawai’i (27), and San Francisco (27).
Besides offsetting chill hours, those warmer than average days can coax fruit trees to bloom too early – before pollinators are active and while frost is still a threat.
“Warmer, shorter winters can disrupt the chill that fruit and nut crops — a nearly $27 billion industry in the U.S. — depend on,” said the report. “Climate Central analysis found that winter chill has decreased in 84% of 215 locations, including in counties that grow the 10 most valuable fruit and nut crops, especially in California, Washington, Florida, Oregon, South Carolina and Georgia.”
Experts expect this trend to continue – which will be problematic for home gardeners as well as farmers. When choosing new fruit trees, berries or perennials for your garden, make sure to consider their chill-hour requirements before planting.
For the full report: https://www.climatecentral.org/climate-matters/2023-winter-package.
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Garden Checklist for week of Jan. 12
Once the winds die down, it’s good winter gardening weather with plenty to do:
* Prune, prune, prune. Now is the time to cut back most deciduous trees and shrubs. The exceptions are spring-flowering shrubs such as lilacs.
* Now is the time to prune fruit trees. (The exceptions are apricot and cherry trees, which are susceptible to a fungus that causes dieback. Save them until summer.) Clean up leaves and debris around the trees to prevent the spread of disease.
* Prune roses, even if they’re still trying to bloom. Strip off any remaining leaves, so the bush will be able to put out new growth in early spring.
* Clean up leaves and debris around your newly pruned roses and shrubs. Put down fresh mulch or bark to keep roots cozy.
* After the wind stops, apply horticultural oil to fruit trees to control scale, mites and aphids. Oils need 24 hours of dry weather after application to be effective.
* This is also the time to spray a copper-based fungicide to peach and nectarine trees to fight leaf curl. (The safest effective fungicides available for backyard trees are copper soap -- aka copper octanoate -- or copper ammonium, a fixed copper fungicide. Apply either of these copper products with 1% horticultural oil to increase effectiveness.)
* When forced bulbs sprout, move them to a cool, bright window. Give them a quarter turn each day so the stems will grow straight.
* Browse through seed catalogs and start making plans for spring and summer.
* Divide daylilies, Shasta daisies and other perennials.
* Cut back and divide chrysanthemums.
* Plant bare-root roses, trees and shrubs.
* Transplant pansies, violas, calendulas, English daisies, snapdragons and fairy primroses.
* In the vegetable garden, plant fava beans, head lettuce, mustard, onion sets, radicchio and radishes.
* Plant bare-root asparagus and root divisions of rhubarb.
* In the bulb department, plant callas, anemones, ranunculus and gladioli for bloom from late spring into summer.
* Plant blooming azaleas, camellias and rhododendrons. If you’re shopping for these beautiful landscape plants, you can now find them in full flower at local nurseries.
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