Here are some factors that influence flowering and fruiting in vegetable crops. The vine crop family has the following factors that cause poor fruit set: Low pollinator activity (lack of honeybees), low temperatures, overcrowded plants and/or excessively dense canopy and lack of pollinator plants (if needed), as with seedless watermelon.

Flowering and fruit set in vine crops are determined by temperature and plant growth rate. Temperature also affects the time of pollen dispersal and how long the flowers remain open. The number of male flowers increase with long days, high temperatures, increased fruit load, more water, high light intensity, high plant populations, excess nitrogen and close in-row plant spacing.

With summer squash, the optimum temperature for growth is between 65º – 75º F. Summer squash is a monoecious plant, as are all members of the vine crop family, meaning that they form separate male and female flowers on the same plant. Both day and night temperature are known to affect sex expression in cucurbits. Cool conditions, especially cool nights, are detrimental to male flower formation and favor female flowers. In general, female flowers tend to form first under cool conditions. In the absence of adequate male flowers, there is poor pollination and low fruit set.

Poor blossom and fruit set in bean, pepper and tomato can be caused by prolonged dry or wet soil conditions, very high (can kill pollen) or very low temperatures, excessive nitrogen fertilization and hot, dry winds. Also, failure to harvest crops regularly can signal plants to slow down flower and fruit production. Night temperatures below 60º and above 75º or day temperatures above 95º can cause pepper flowers and small fruits to drop. Plants often stop producing blossoms and fruits during mid-summer if temperatures are high. Fruit production then resumes on healthy plants in late summer and early autumn. Tomato flower and fruit production diminish when temperatures are below 55º or above 95º. Furthermore, low spring temperatures will often cause the first cluster of fruits to be deformed. This is known as catfacing. Eggplant does not set fruit well until minimum night temperatures exceed 55º. Bean plants stop flowering or flowers die when temperatures exceed 85º.

Sweet corn is another vegetable adversely affected by high temperatures. The corn tassel is often killed when temperatures go above 100º. Injury to the tassel will prevent development of kernels in the ear. Fortunately, in most parts of the country, summer temperatures don’t stay above 100º for long.

Fruit & Vegetable Ripening

Ripening is the process by which fruits attain their desirable flavor, color and textural properties. Climacteric fruits can ripen off the plant once they have reached physiological maturity. Climacteric fruits include apples, avocado, blueberries, fig, muskmelon, pears, persimmon, quince, stone fruits and tomato. If harvested “mature-green,” some of these fruits can be ripened after harvest and given short term storage. Pears are unusual in that they develop the best flavor and texture characteristics when harvested mature-green and ripened off the tree. Avocadoes do not ripen on the tree.

Some climacteric fruits give off large quantities of ethylene, a naturally occurring growth hormone, which triggers ripening. A small dose of ethylene gas will stimulate other climacteric fruits to begin the ripening process. A few climacteric fruits, such as muskmelons, will not increase in sugar content after harvesting, but will soften.

Non-climacteric fruits must ripen on the plant if you want a fully ripe fruit; once they have been harvested, no further ripening will occur. Flavor and texture will be of low quality if fruits are picked before fully ripe. Some non-climacteric fruits include berries, cherries, citrus fruits, cucumbers, eggplants, grapes, okra, peas, peppers, strawberries, summer squash, tamarillo and watermelon.

Non-climacteric fruits will not respond to attempts to ripen them with synthetic ethylene gas. A partially red strawberry, for example, will not develop any more color or sweetness after being picked, and will deteriorate faster if exposed to ethylene. Watermelons develop most of their sweetness during the week before they reach full maturity, making early harvest very undesirable.

Sometimes ripening commodities with synthetic ethylene before sale at the wholesale or retail level will improve their value. Ripening rooms are often used for tomatoes and citrus fruits. A small fan can be used to ensure a uniform, continuous flow of ethylene into and through the room. Forced-air ripening is increasingly being used to provide more uniform temperatures and ethylene concentrations throughout the ripening room.

Ripening information was adapted from “Small-Scale Postharvest Handling Practices: A Manual for Horticultural Crops (4th Edition),” University of California at Davis, November 2003.