Gardeners are often faced with the dilemma of knowing when to harvest fruits and vegetables. When is the right time to pick them, and will they ripen afterward? At the risk of revealing that I am a botany nerd, fruit are the protective female organs of flowering plants that contain their babies, or seeds. The protective fruit may be fleshy structures, like apples, or dry structures, like nuts. Apples, peaches, grapes, tomatoes, peppers and melons are all examples of fleshy fruit.
Physiologically, fruit are mature when their seeds are fully developed. However, if you have ever encountered a humongous, fully mature zucchini, you will know that the desirable stage for harvesting and eating this fruit is when they are much smaller with tender skin and undeveloped seeds. As consumers, there are some vegetable fruits that we prefer to eat when they are immature, like summer squash, and others when fully mature, like melons. When it comes to tree fruit, like apples or peaches, we usually find the fruit much tastier when fully mature and ripe.
Ripening is also a physiological process. It involves changes in the fruit, such as the flesh becoming softer and sweeter, and the skin changing from one color (often green) to another. Chemical changes can occur during ripening, including the breakdown of starches into sugars, leading to a sweeter flavor. Softening results from a change of insoluble pectin in the cell walls to soluble pectin. The acid content of the flesh also decreases as the fruit ripen.
Now back to the original question of when to pick fruit, and if they will ripen off the plant. The answer: Some do and some don’t. Because of this, horticulturists divide fruit into two groups. The group that does not ripen after picking tend to produce only small quantities of ethylene gas as they ripen. Ethylene is an odorless, naturally occurring hydrocarbon gas. It is sometimes referred to as a plant aging hormone. Fruit that do not ripen after picking include cherries, grapes, raspberries, strawberries, other berries, watermelon and citrus fruits. These are picked when fully mature and ripe.
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The second group are fruit that produce greater amounts of ethylene as they ripen and do ripen after picking. These include apples, pears, peaches, nectarines, apricots, plums, cantaloupes, bananas and tomatoes. These fruit should be harvested at the right stage of ripeness after becoming fully mature. I am sometimes asked how to determine when to pick homegrown apples. It is tricky because the timing is based on the color of the skin, how easy it is to detach from the tree, flavor and softness.
Commercial fruit growers have equipment for testing skin color, amounts of sugar and flesh firmness. Gardeners should periodically check for sweetness by tasting the fruit. The flesh will be starchy if it is not ripe. Gardeners can also check the fruits’ aroma and judge skin color.
Apples change in firmness from rock hard to slightly softer flesh that gives just a bit with a press of the thumb. Ripe apples should separate from the tree fairly easily with a slight upward twist. A gardener must sacrifice a few fruit to determine the right time, but it is better than harvesting an entire crop of unripe or over-ripe fruit.
Now that fall is here, I suspect frost is not far off, so next week we will tackle picking winter squash and green tomatoes.
Marianne C. Ophardt is a horticulturist for Washington State University Benton County Extension.