Fruit Set Failure

Why do healthy plants fail to set fruit? Your plants look lush and healthy. There are plenty of leaves and blossoms. You’ve been watering and feeding and mulching, just the way you are supposed to, and still no fruit. Why not?

Tomato blossoms (Kate Russell)

Assuming that your plants are otherwise healthy, not diseased or water stressed, there are several reasons behind fruit set failure. The most common causes are lack of pollinators, too much heat, not enough light, and the wrong fertilizer.


Lack of pollinators
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While many crops, such as tomatoes, are self-fertile, the lack of bees, flies, butterflies and moths, and even wind can reduce the number of fertilized flowers. Unfertilized flowers cannot produce fruit. You can attract more pollinators into your garden and landscape with colorful flowers that offer a variety of landing pads. Plant flowers in clusters, rather than singly, for the best results. You can shake plants very gently to increase pollination rates.

Honey bees (Kate Russell)

Too hot to fruit

One of the most common reasons why blossoms do not transform into fruit is heat. As temperatures rise, plant life processes slow down. Most spring temperatures are pretty mild, but a few scorching hot days can ruin everything, at least for a while. This is because pollen loses its viability between 85 and 90 ºF. So it won’t matter how many bees stop by for a visit or how healthy your plants are. It simply can’t happen. Luckily, most plants continue to produce flowers beyond the brief heat wave and the pollen in those flowers can produce fruit. Note, hybrid plants tend to be more sensitive to temperature fluctuations.


Inadequate light

Most fruiting plants need six to eight hours of sunlight to produce. If growth is leggy and etiolated, it may be that they are not getting enough light. Chlorosis is also common when plants are not getting enough sunlight. This is called etiolation.


Fertilizer, a balancing act

All plants need good nutrition to produce fruit. Unhealthy plants simply do not have the resources to produce a decent crop. At the same time, too much nitrogen can lead to excessive vegetative growth, and even blossoms, and still no fruit. Insufficient phosphorus can also cause reduced flowering and fruiting, but that is rarely a problem in San Jose, California. Before adding phosphorus (which we generally have in excess), or any other nutrient, send a soil sample in for testing. Soil tests are inexpensive and invaluable. Too many nutrients can cause just as many problems as not enough.


So, if you are watering your plants properly and they are getting enough light, you may simply need to wait out the unfavorable conditions, or you may need to alter your fertilizer applications.