Deciduous fruit trees demand to spend their winters in certain ways. Peaches, plums, apricots, apples, cherries, nectarines, they like to get chilly in the fall, then shed their leaves and stay chilly for a certain length of time, then warm up in the late winter or early spring and make flowers — a bunch of flowers all at once.
Pictured above are some of my stone fruit trees making a bunch of flowers all at once. They are telling us that they had a fantasticly chilly winter. They are suited to the past winter’s climate in my yard.
On the other hand, the same trees were sending a very different message at this time last year, after an unusually warm and wacky winter. (See my post about last winter, “Effects of a warm and wacky winter on deciduous fruit trees.”) Here is my Flavor King pluot “in bloom” last year:
And here it is this year:
How do your deciduous fruit trees look this spring? Are they flowering in a heavy, concentrated way? If not, then don’t expect them to in the future. They probably aren’t going to experience a more consistently cold winter in Southern California anytime soon.
What kind of winter did we have?
Many parts of Southern California had a winter for the record books, just like my nook of San Diego County did. I’m in an area called Ramona, and the National Weather Service says that in February we had the coldest average temperature ever recorded: 47 degrees.
More important for deciduous fruit trees, January and December were also consistently cool. The winter of 2018-2019 was three successive months of steady chill. I keep temperature records for my yard, and the highest temperature between December 1 and March 15 was only 71 degrees. And in February there were two full weeks where my yard did not even rise as high as 60 degrees. That’s cool, consistently cool.
We never even had our usual Santa Ana spell around New Year’s. It was the best winter for deciduous fruit trees that we can hope for, ever.
What do deciduous fruit trees want from a winter?
Deciduous fruit trees of all types vary slightly in their winter preferences in terms of how long the winter lasts and how cold it gets, but they all seem to have an internal clock that counts how long it stays cool and whenever they’ve reached their requirement (and the air warms up), they wake up and flower. A Babcock peach only needs to be chilly for a short time while a Bing cherry needs to be chilly for longer than our winters ever last in Southern California.
(For more about winter chill needs of deciduous fruit trees, see my post “Effects of a warm and wacky winter on deciduous fruit trees.”)
Researchers are continually learning more about exactly what deciduous fruit trees need in their winters, and last week I listened to an interesting interview with one such researcher named Katherine Jarvis-Shean of the University of California. About the fact that trees prefer consistent chill, Jarvis-Shean likened winter to filling a bucket. Cold nights fill the bucket, but a winter warm spell (Santa Anas near New Year’s, e.g.) dumps out some of the accumulated chill.
Jarvis-Shean also noted that during unusually warm winters pollenizers sometimes don’t bloom at the same time as the trees they’re meant to pollenize. Pluots, for example, need to be pollenized by another pluot or certain plums. Unusually warm winters will cause these trees to bloom at different times compared to when they meet their chill requirements in a colder winter.
I saw this at work with my pluots and plums last year compared to previous years — and compared to this year. I even shot a short video of some of them in bloom here:
Synchronicity of bloom should result in a ton of pluots this summer. I’m starting to see flower petals dropping and fruitlets appearing today.
And here is a short follow-up video shot on May 2, 2019, showing the actual fruitset on my pluots:
What does all this mean for our yards?
This year is the time to consider removing deciduous fruit trees that don’t set a good crop or figuring out what else is wrong because these apricots, cherries, plums, pluots, peaches, nectarines, apples, etc. all experienced the coolest winter they will ever give it.
What are the other possible problems for a deciduous fruit tree not fruiting well this year?
Earlier today, I had a wonderful time speaking about fruit trees to the Carlsbad Garden Club, and I was reminded of the myriad other factors that can be holding a tree back from fruiting as one hopes.
For instance, one garden club member mentioned that she has a plum tree which flowers profusely every year but barely sets a couple fruit. Many plums need to be pollenized by another plum tree so my suspicion in her case is that the problem is not chill, but rather that her plum needs a mate. (For more on this issue, see my post “Grafting a pollenizer branch into your fruit tree.”)
Also, if a tree has only been in the ground in your yard for a year or two, then make no conclusions yet. Some trees need to grow for a couple years before they develop fruiting wood. This is especially applicable to cherries, but all trees should bloom and fruit more as they get older.
Not enough sun can be a problem, but that’s not the issue with my SpiceZee nectaplum. I’m keeping a close eye on this tree. The tree’s bloom last year was weak, which I ascribed to the warm and wacky winter.
Disappointingly, this year’s bloom isn’t far better.
But since the tree is still young (planted as a bare root in January 2017), I’m forgiving its moderate bloom and hoping that it sets a moderate crop. At this date, it’s still too early to tell.
It’s possible to make the mistake of pruning off most of a tree’s fruiting wood, too — I’ve made that mistake before. (See my post, “Don’t cut off the fruiting wood: Pruning lesson number one.”)
One final thing to remember is that trees have different schedules. Most apples wake up from the winter later than other kinds of trees. My Pink Lady apple is only swelling its first couple buds today whereas my Blenheim apricot, which is adjacent, is already finished flowering. This is natural and nothing to worry about.
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