Sunny Slope Orchard

Sunny Slope Orchard
In the coast range foothills overlooking the Sacramento Valley

Sunday, May 8, 2011

Fruit Thinning

We've just about finished the tedious task of thinning excess fruit from the trees. Thinning is a vital step in fruit tree care that many backyard gardeners neglect, while others may not realize that it should be done at all. But given the right growing conditions most stone fruit trees will set far more fruit than they can support. Unless much of the excess is removed, both fruit quality and tree health will suffer. Trees that typically need thinning are apricots, peaches, plums, pears and apples. Cherries, figs, persimmons and citrus usually do not.

Here are the benefits of thinning:
  • Thinning matches the tree's energy with the amount of fruit it has to nourish. A tree has only so much carbohydrate stored in its roots, so when too many fruits compete for this nourishment they all end up small and flavorless.
  • Thinning reduces disease and insect damage. Crowded clumps of fruit offer hiding places for damaging insects, which can then damage all the fruits in a group. Crowded fruits also stay wet longer in damp weather, encouraging mold and fungus problems that can quickly infect all adjacent fruit.
  • Excess fruit weighs down branches, especially when trees are not adequately pruned. This often leads to broken limbs.
  • Crowding shields fruit from sunlight, decreasing fruit color and flavor.
  • Thinning is an opportunity to remove smaller, deformed or damaged fruit so more of the tree's energy can go into the remaining perfect fruit.
As we admire small green fruits early in the season and dream of biting into a ripe peach or apricot later on, it can be really hard to pull fruit off. But as with pruning, this is not a time to be squeamish. Apricots should be left no closer than 3-4" apart, and peaches no closer than 6-8". Fruit at the ends of long branches should be thinned even more heavily to avoid breakage in a wind storm. On a heavy year we will often need to remove 90% of the fruit from a tree, leaving the ground littered almost solid with small green fruits.

Apricots before thinning . . .

Timing of thinning is important too. Most trees will self-thin to some degree; at an early stage some fruits will yellow and drop off on their own, so it is important to wait for this to happen before manually thinning. But once that happens we like to thin right away, so the remaining fruit will get the most benefit. Leaving too much fruit on also starves the tree which then reduces next year's crop, so it is always better to thin more, not less!

and after the first thinning
 Thinning can be done by knocking with sticks, but we prefer doing it by hand. It's a lot more work, but gives us much better control and hence more benefit. Ideally the smallest fruit should be removed in favor of the largest.

Peaches before thinning . . .

We will typically thin twice, the first time leaving a few too many to cover our bases in case a bad hail storm or wind should damage much of the fruit. Then after 2-3 weeks when the fruit has sized up a bit more we go back and get more agressive.
and after the first thinning

The pictures at right show a typical before and after first-thinning look at cots and peaches. The second thinning will remove even more fruit. It hurts to do it, but always pays off in fruit size and quality. After 40 years I don't remember ever thinking we thinned to heavily.