In a time of food insecurity, what could be more inviting than a tree covered in fruit? Then again, sometimes the gods can be too kind. Overly generous fruit loads have a way of breaking branches and yielding small, poor-quality fruit if not managed in a timely manner. 

When most families depended on their own gardens to supply the kitchen season-by-season, everybody understood the paradoxical nature of ridding the tree of a sizable amount of its developing fruit in order to get a decent harvest. This might seem an absurdity to today’s hands-off consumer! 

But culling, or thinning, a tree of excess fruits before the majority have reached the size of a quarter does stop them from crowding one another, competing for the tree’s resources and putting too much weight on the branches. In a frustrating twist, this allows too many young fruits to mature on the tree and causes the tree to cancel much of next year’s crop. 

The tree does this because next year’s crop is already present in the form of latent buds. Every seed in every fruit is programmed to secrete a hormonal signal that the tree can interpret and react to in order to save its own reserves by nullifying any number of those latent buds. Culling, therefore, interrupts any tendency for the tree to produce too much fruit one year, none or a scarce crop the next and will ensure a crop can be harvested next year, too.

For gardeners, the key issue  when culling is how much space to leave between each new fruit. For plums, apricots and pluots the spacing should be 3 to 4 inches apart; peaches and nectarines need 5 to 7 inches and apples should be culled to one or two per cluster. Trees that typically don’t need culling include: figs, pomegranates, cherries and citrus. 

In the case of persimmons, the amount of immature fruit drop throughout the summer is often enough to be unnerving, and even more will drop if the tree was fertilized while in blossom or developing its fruit.

For detailed information on the process of fruit thinning, visit the University of California Master Gardener Program’s excellent online guide “The California Backyard Orchard” at http://homeorchard.ucanr.edu/The_Big_Picture/Fruit_Thinning.