Few tomatoes in your garden?

Severe drought conditions could be causing poor fruit set on tomatoes in home gardens.

I will be so happy when the 2012 gardening season is over. The extremely warm weather in March resulted in early plant development that was damaged by subsequent frost and freezes. Estimates of damage to agricultural crops are expected to exceed $300 million in Michigan. As a result of the strange weather, I lost all of my apple, pear, peach and cherry crops.

If that wasn’t enough, many areas in Michigan are now experiencing severe drought conditions. Crops such as blueberries, ever-bearing strawberries and corn on non-irrigated land are showing signs of stress. As the temperatures reach into the 90s, I expect to see another problem: poor fruit set on tomatoes.

Tomatoes are an interesting crop in that they can be pollinated by certain species of bees, although the blossoms are not that attractive to them and some pollination results from the vibration of the plant by the wind. When the weather is very warm, pollination may not take place, resulting in a drastic decrease in yield.

It is not unusual in years like this one to receive calls from gardeners asking why they have plenty of blossoms on their plants, but no fruit. The answer is multifaceted, but I will try to keep it simple.

Tomatoes have perfect flowers. This means they contain both the male and female organs. In order to get fruit, two things need to happen:

  1. Pollination, which is the transfer of pollen from the male organ (stamens) to the female organ (pistil).
  2. Fertilization, which is the merging of genetic material resulting in the growth of a fruit.

Weather conditions can have a significant role on this process. For example, when the plants are exposed to temperatures below 55 degrees Fahrenheit or greater than 75 degrees Fahrenheit, the pollen produced may be sterile. If the humidity is too high, pollen may stick together and not shed from the anther easily. If the humidity is too low, it may not stick to the stigma once released.

The ideal conditions for pollen shedding are warm, sunny days, usually between 10 a.m. and 4 p.m., but plants will set fruit most efficiently when the night temperatures are between 60 and 70 degrees Fahrenheit. Unfavorable temperatures, humidity, wind speed or lack of pollinator activity can all contribute low fruit set. Little or no fruit set means a sparse crop. What can be done? Nothing, but pray for cooler weather and a longer growing season.

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