CRFG "Fruit Gardener" October 1993
Thin That Fruit!
An overloaded tree is an unhappy tree, possibly an unhealthy tree, and certainly a tree likely to produce inferior fruit. Eph Konigsberg, in a talk to the Foothill chapter offered ten excellent reasons why fruit thinning should be a part of any orchardist’s tree-maintenance program.
1. Fruit size: If you thin, you can get good- sized fruit. If you don’t, you’ll get undersized fruit. Perhaps you will have a greater number of fruit if you fail to thin, but you will probably not like the ratio of pulp to pit. Eph follows a handy two-part rule: When it comes to larger fruits such as peaches, Casimiroa edulis (white sapote) or apples, if you can touch two fruits with one hand, you are allowing your tree to bear too much fruit. On trees or bushes bearing small fruits such as eugenias or mulberries, if you can touch two with one thumb, thin it out. By following this rule, the plant will produce the largest fruit possible up to its genetic potential.
2. Sweetness of fruit: The tree is best able to develop the necessary sugars and therefore sweetness, by putting its energy into a smaller number of fruit. Although you will get fewer individual fruits per tree, they will be of much higher quality.
3. To avoid limb breakage: Limbs overloaded with fruit often break and fall onto the ground. They do so in a random and uncontrolled way that usually tears bark, thus exposing the tree to fungus and insect attack. Eph advises that if the limb can’t bear the weight of the fruit, thin the fruit. Don’t prop up the limb. It hurts the tree in the long run.
4. To avoid disease: If wind and air can’t go through the tree and circulate between the fruit you have an increased potential for disease.
5. To reduce a tendency toward alternate bearing: A tree puts a lot of energy into producing and ripening fruit. Heavy fruit set demands a heavy expenditure of energy, and the tree will need to recuperate from this. For instance, a pear tree left unthinned during a heavy-bearing year might produce a big number of small-to-medium-sized fruit, then next year, none at all. By thinning out the very heavy fruit sets, you can avoid this problem. Exception: some varieties are genetically programmed to be alternate bearing. There is nothing you can do about this. However, even in these cases, the heavy crops should be thinned because of all the other excellent reasons listed.
6. To avoid weakening younger trees: Allowing a very young tree to produce fruit retards its growth.
7. To control fruit drop: Trees do this spontaneously. If the fruit set is not thinned, they might drop all, or at least most of their fruit.
8. To stagger the fruit-ripening process: If you look at fruit set on most trees, you will see little green nubbins of varying sizes, indicating differing stages of development. If you thin fruit so that some remain in each of the various stages of development, you will be able to spread ripening over a much longer period. That is, the more developed fruits remaining will ripen first, the others, later. Eph described an experiment he is performing on his Anna apples. He has two Anna apple trees. These set three crops a year, a good first crop, a moderate second crop and a small third crop. Last year he thinned an exceptionally heavy first crop and got a good second crop. This year he is thinning all of the first crop to see its effect on the second crop. A year from now, he plans to pick off all the first and second crop and see if this produces a large third crop.
9. To enjoy the green fruit: He cites the examples of green mango chutney, the deliciousness of green apple pie. Green papaya can be used as a vegetable. Most people never thin enough when the fruit is small. Eph suggests that when the fruit is about the right size, do a second thinning and use this green fruit in cooking. Consider it a resource.
10. To improve the appearance of the fruit. Some fruit should be thinned to ripen as far inside the tree as possible. This applies to fruit easily sun scalded such as persimmons or loquats. Thin the fruit on the outside. Other types of fruit, such as peaches and some varieties of apples, should be thinned on the inside of the tree because they need exposure to sunlight to color up.
Tricks Learned from Experience
Eph restricts all his trees to a height of 8 feet and explains his reason with a question: How do you thin a 35-foot tree (especially when you get beyond a certain age and find yourself disinclined to go scampering up ladders or tree trunks)?
He cautions that trees should not be allowed to develop canopies. He used as an example a peach tree of his. He wanted to keep most of the growth in the lower branches, but these were dying off. Therefore, he was not getting the results he wanted: good lower branch development and most of the fruit developing there, within reach. He realized his problem was the canopy of leaves above. It shaded everything; no sunlight could penetrate the heavy growth above. So he summer-pruned to allow sunlight into the interior and reach the lower branches.
Another way to keep a tree small is to restrict its growth by means of root pruning. When a Varigold lemon planted between two larger trees failed to thrive, Eph dug trenches between it and the larger trees on either side. The trench restricted root growth of the larger trees and kept the roots from encroaching into the root zone of his lemon. The trench should be approximately at the drip line. If you dig it inside the tree’s drip line, then cut back the top of the tree. However, Eph cautions that if you do this with jujube, you get rootstock.
Some of the results of natural thinning can be startling. It is not unusual for the first crop a tree bears to be sparse: two or three fruits or nuts. On occasion this can result in enormous fruit, unduly exciting the novice or orchardist. The second or third year’s usually more prolific fruit set is probably more indicative of the likely size of the new fruit or nut strain in the mature tree.
For his strawberry guavas, Eph took yet another approach. When one of his plants almost died from the stress of an enormous fruit set, Eph knew he would lose an entire afternoon thinning that strawberry guava. So he took a shortcut. Strawberry guavas grow in bunches. Instead of thinning the fruit individually, his solution was to get rid of some of the bunches. Cutting out bunches with a tool had the same good effect as thinning individual fruits.
Eph cautioned against the shortcut of using chemical sprays such as those used in commercial orchards to thin fruit. The reason is that those products are designed for a large planting of one species. Home gardeners or very small-scale fruit growers tend to have one or a very few of each kind of tree—maybe a plum tree, nearby a peach, and next to it a nectarine, across the yard a Minneola tangelo, around the side of the house a persimmon—a smattering of different kinds of trees. A chemical that causes controlled thinning in one species might affect another differently.
Thin loquats while they are still in flower. Lop off every other cluster, taking care to leave quite a few toward the top of the tree - fruit tax collected by birds. If you leave some fruit for the feathered bandits toward the top, they will be less inclined to bother the loquats growing toward the bottom of your tree.
Thin persimmons in the flowering stage, too. This is important because persimmons are another one of those fruit species prone to premature fruit drop from an overloaded, unthinned tree. You can lose most of a crop this way.
Especially with figs, pruning can also be considered a form of thinning. Most figs grow on new growth. "Breba" is the smaller, earlier crop that comes out of the previous year’s growth. When pruning your fig trees, always leave one half of the tree unpruned to get a breba crop.
In concluding his talk, Eph ran down a few fruit trees needing further research and experimentation:
Pitangas will produce a fine crop of seeds with skimpy pulp if left unthinned. He expressed the need to develop a way to thin pitangas easily.
To improve his macadamia nut yield, he plans to experiment with taking a pole pruner and knocking off every other bunch.
The bottom line is, if you want larger and sweeter mulberries and peaches, giant medjool dates, healthier trees, and an extended crop, go out there with pruning shears or even scissors and thin your fruit. You‘re aiming for quality first and foremost. If you want average produce, you can always go to a supermarket
Alice Ramirez is a contributing editor of the FRUIT GARDENER who reports frequently on various horticulture meetings.