There is an old Spanish proverb that is used in reference to both childrearing and training of trees and vines:  “El palo que nace chueco jamas se endereza” (A crooked branch will never straighten).
If you travel to a region where tree crops are grown, you will notice that the trees in an orchard always look the same.  Not just that they have the same leaves and fruit, but that the shape of the tree varies very little from one to the next.  This is the result of careful shaping according to a set of rules established over time and followed by most farmers.
Apple trees are not shaped the same as apricots, nor are cherry trees shaped like cherimoyas.  But make no mistake:  each of those trees was shaped by human hands, with a pruning shears and a saw.
Shaping begins from the minute the tree is planted, when the top two-thirds are cut off.  This encourages the trees to push out new roots and get acclimated to its new home.  Later the same year, after the tree pushes out new branches, more pruning cuts are made.  Branches that cross or grow “backwards” into the center of the tree are eliminated.  And the tree gets shaped based on one of a few blueprints:  an “open vase” shape with three or four “scaffold” branches; a center-leader that is usually tied to a stake to keep it straight; or one of various “cordon” systems that force a tree or vine to grow parallel to the ground along a wall or trellis.
As the trees grow, the farmer continues to follow the established system of pruning.  The shape of the tree is maintained, and certain cuts are made to encourage production of fruit or nuts.  Failure to prune the tree even in a single year can cause numerous problems, ranging all the way from overproduction of fruit that subsequently causes broken limbs to excessive shading by foliage that results in little or no crop.
So when the University of California came out last year with a study challenging many of these assumptions, it was a bombshell.  They compared several training and pruning methods for new walnut trees to a unpruned control and found no difference in crop production over a seven year period.
The results surprised even the researchers, who like anyone else in the business have spent their whole lives shaping trees.
“Just let ’em grow” is the basic conclusion of the research.  Yes, some branches — and even some whole trees — will break.  But it turns out that nut trees (walnut trees anyway) pretty much know what they are doing.  They will fill up all the available space and sunlight available to them, and use it to make as many nuts as they can.  And by letting them do it on their own, farmers can save many hundreds of dollars per acre on pruning costs.
By coincidence, we happened to plant a walnut orchard last year so we try out the new “system”.   I can say one thing about the results:  it ain’t pretty.  Every tree in our 8 acre orchard looks completely different.  Some are tall and straight, others are short and bushy.  We had a windstorm last week and the trunks of several of the tallest trees simply snapped halfway up.  But none blew over completely, and the broken trees are already responding to the damage by pushing out new growth.
One year-old walnut trees at sunset
One of the main benefits to the new (non)-pruning regime is that the trees produce their first harvest two years early than under the old system, in which you intentionally cut off nut-producing branches for two full years.  In fact, many of our trees already have a  handful of nuts on them.
 I’ve seen a few other new walnut orchards around the area that look like ours, but most growers are obviously ignoring the UC recommendations and sticking to their tried and true methods.  I’m not surprised.  Farmers are used to dealing with plenty of factors beyond their control, but traditionally, the shape of their trees has not been one of them.  A uniform and well-organized orchard is a way of maintaining a bit of sanity when everything else seems chaotic.
Since we have never planted a walnut orchard ourselves, we aren’t wedded to any existing system. And our new orchard is well off the road where no one can see it except us.  So I won’t have to put up with any of our walnut farmer neighbors telling me, “You know, el palo que nace chueco…”