Joan Swenson: On a clear day you can see forever — but the fog is better for your fruit
| Thursday, Dec 18 2008 07:09 PM
Last Updated Friday, Mar 27 2009 01:50 PM
Do I like the fog?
Better question — do I like shivering in the half-light of Bakersfield’s foggy winter days and do I like wearing two pairs of socks inside my slippers at night even with the heat on?
Not really, but my fruit trees like fog. And some like it a lot better than blindingly bright, icy winter days that can quickly turn to freezing, citrus fruit-killing nights. Think of fog as a lovely insulator, like the pink stuff in the attic that keeps temperatures from dropping too low. It’s the protector of sensitive crops, the moderator of chilly air.
All those foggy days when the temperatures start in the 30s and linger in the middle 40s? Perfect for deciduous fruit and nut trees. These need to be chilled to do well, each with their own number of hours of chill — temperatures below 45 degrees — for the trees to produce well next year.
This is why, when you choose a bare root fruit tree, you should buy it at a nursery where the staff has purchased trees specifically for your area. An apple tree in Tehachapi would not be the same variety you want to plant in Bakersfield because Tehachapi gets substantially more chill hours than Bakersfield. You’d need a low-chill requirement apple in Bakersfield. Tree tags typically explain how many chill hours a tree requires.
The valley floor in the past has had approximately 800 chill hours from mid-November to mid-February each fall-to-winter — although we all know it’s chilliest from mid-December to mid-January. However, the average has been dropping lower each decade and researchers at UC Berkeley have predicted that by the end of the 21st century that the valley will have an average of 500 chill hours per season. Lack of chill hours and warm winters can cause trees to bloom too early and lead to poor fruit production.
Farmers and gardeners will need to plant low-chill trees.
On the valley floor, there is a wide range of chill hours depending on location. Arvin will have about 200 hours fewer chill hours than Shafter. Even parts of Bakersfield may be warmer than others.
Sunny, bright days that are chilly are not as good as gray, foggy days for producing enough chill hours. Interestingly, while the air temperature may be 44 degrees on a sunny day, the sun shining on a tree can warm it up enough to essentially void those chill hours.
Clear, open skies in the winter can produce freezing temperatures as the earth’s heat rises at night. Freezing temperatures aren’t bad for deciduous fruit trees, but they can be murder on citrus. Ripening citrus can hang safely on trees for many weeks, unless we get an extended, hard frost. If frost is predicted, you may run water around your citrus trees to slightly raise the temperature around the trees. Extended days of freezing temperatures? Pick your fruit immediately and get it into a cool, but not freezing spot, such as a garage.
And meanwhile, praise the fog that keeps our peach trees producing and our citrus trees protected.
