Citrus fruit has been one of the symbols of California agriculture for over a hundred years.  While they are tropical plants, citrus trees thrive in warm temperatures and tolerate arid environments as long as they are irrigated.  Some of the oldest orange trees in the state grow just across the road from our farm, at the UC Davis Wolfskill Ranch.  More than century old and impossibly tall, they were planted by John Wolfskill after the land was granted to him by the Mexican government.  Seeing those trees, you might be left with the illusion that all it takes to grow citrus is to stick them in the ground and they will essentially live forever.  Nothing could be further from the truth.
Citrus are unlike almost every other fruit grown in our state in two ways.  First, their fruit ripens in the winter and early spring, instead of the summer and fall.  During this time, it is constantly at risk from temperatures dropping below freezing.  Second, evergreen citrus do not go dormant in the winter.  Mature trees can be damaged if it gets below 25 degrees or so, and killed by temperatures in the teens.
But citrus is most vulnerable to being killed by a freeze when the trees are young, their roots are still small and poorly established, and they don´t have much leaf canopy to keep their trunks warm.  A single night below 25 degrees will kill a tree less than a year old.  Weather this cold is not infrequent in the “citrus growing regions” of California, once or twice every ten years.  Once the trees get to be six years old, they can handle much more cold.  So the survival and success of a citrus orchard depends enormously on the weather for the first few years of its life.  In other words, John Wolfskill got lucky when he planted those first orange trees.
Everywhere in the world that they grow, oranges are orange on the inside.  But despite their tropical origins, the peel of the fruit does not fully color unless it gets chilly — into the low 50s.  Oranges can be ripe and sweet and still be mostly green on the outside.  But in the U.S., few people will buy a half-green orange.
The arrival of the cool fall weather that makes citrus turn color in California is normally accompanied by frequent rains that complicate the harvest.  Itś not safe to climb tall ladders to pick the fruit in the wind and rain.  If the ground in the orchard is too wet, you can´t get in with a tractor or trailer to haul the fruit out.  And anyway, citrus that is harvested when itś soaking wet tends to quickly get moldy unless it is quickly dried.  So harvest happens between storms.
All of these elements combined make citrus growing a challenge requiring a Zen-like level of patience combined with Ninja speed:  Wait, wait, gogogogo, stop, wait, wait, go.  In our own experience as citrus growers, there have been years when warm weather has lasted well into November, keeping the fruit from coloring up — only to be followed by weeks of constant rain preventing us from harvesting.  Then, after a day or two of harvest, a freeze that destroyed part of the crop.
Some farmers say that growing citrus is like playing Russian Roulette with 3 bullets instead of 1.  Itś not a crop you want to rely on for your living.  All of our citrus orchards are planted on other peopleś land, and all of those people have regular jobs.
All that aside, growing citrus is deeply satisfying on other levels.   Walking into a vibrant. lush green orchard loaded with ripe fruit in the middle of winter can chase away the worst case of winter blues.  And the fragrance is amazing.  Not to mention the bright, delicious fruit.
We harvest a succession of citrus at Terra Firma, first mandarins, then navel oranges and finally grapefruit.  Our mandarins have sweet on the inside for a couple of weeks, but have stubbornly resisted turning color due to the hot weather — we had a record high temperature of 87 degrees here Saturday.
But over just 24 hours, we had a dramatic weather change with Sundayś healthy rainfall that ushered in much cooler — normal — fall weather, and the mandarins responded immediately.  We started harvesting mostly orange fruit yesterday, and with chilly temperatures forecast all week, we expect them to be completely orange by the weekend.
You can look forward to a fairly steady stream of citrus in your boxes this winter…with the enormous disclaimer that we need it to be not too cold and not too wet.  What could possibly go wrong?