Citrus Freezes - Location Helps

Citrus Freezes – Location Helps
February 2007
Thaddeus Barsotti

Ever since I can remember my mother used to point out gently sloping hills in the Capay Valley. They were always pretty locations, big golden hills painted with shadows from the sun and oak trees sporadically filling the landscape. The spots she was interested in were hills that had flattened out enough to farm but still remained well above the valley’s floor – spots that cold air would “roll right off of” as she used to put it.

Cold air is much more dense that hot air – farmers pay particular attention to this when selecting a location to invest an orchard that is sensitive to freezing temperatures. We were interested in growing citrus. These trees are tropical plants, and quite frankly, were never intended to survive Northern California’s winters. To a citrus tree our area’s occasional freezing temperatures are death – briskly disguised.

Citrus trees are only in danger during the extreme cold periods of our valley – which creep below the freezing point. This cold, dense air is pulled down by gravity, displacing the warmer air to higher elevations. The result is that the coldest air temperatures are at the lowest elevations, while the higher elevations are surrounded by air several degrees warmer than the rest of the valley – this is called an inversion layer. It may not seem like much, but these few degrees can be the difference between an orchard that is killed and one that creeps by to live another season.

It is no wonder my mother taught her children the value of these few degrees. In the frost of 1988, she lost a young Satsuma Mandarin orchard - while the orchard a few hundred yards up the hill survived. This was an expensive lesson and surely a lesson a parent would not want her children to learn the hard way.

When I drive around our valley today I still recognize those perfect spots - high enough to scare away the cold but tame enough to farm. I can see what the orchard would look like to people driving by – a green patch in the quilted layers of grasses, shadows and trees that make the hills. It crosses my mind that those spots are important for only a few weeks of the twenty or so years a citrus trees is producing; but the importance of those moments are paramount events in the orchard’s life. Those moments are what allow the orchard to continue to work for the farmer who placed them there.

Many orchards and farmers are feeling the effects of the cold snap that just covered the state. It is estimated that 75% of the states citrus crop was lost this year. The percentage of the orchards that were killed will be determined this spring. The orchards and crops that survived were in abnormally warm micro-climates or at elevation that escaped the cold air below.

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