Can Ultrasound Accelerate Plant Growth?

Though it's best known as a pest-control method, high-frequency sound could soon be used for ultrasonic plant stimulation.


| May/June 1984



Plant Growth Sound Frequency

Fig. 1: The hearing capabilities of several different mammals are compared to the frequency range effective for plant stimulation. Higher frequencies seem to stimulate greater growth.


ILLUSTRATION: MOTHER EARTH NEWS STAFF

In an effort to keep you informed about the latest developments in the scientific and electronic worlds, I regularly devote time to reporting current (as well as, occasionally, forgotten) technology. Two issues ago—in How a Solar Root Stimulator Can Help Grow Healthy Plants—I discussed some experiments in which photovoltaic cells were used to stimulate the roots of plants, resulting in a significant increase in the rate of plant growth.

And, as it happens, I recently found yet another intriguing report... one which claims that plant growth can be speeded up by subjecting the greenery to ultrasound. "Now this," I thought, "is a new twist."

Ultrasonics 

Judging by your overwhelming response to the article on photovoltaic root stimulation, I'm sure that many of you will be anxious to give this new technique a try. Once again, though, let's start by discussing the principles behind this exciting development.

Sound is vibration that travels through air. Without those molecules of nitrogen, oxygen, carbon dioxide, etc., there would be no sound: A telephone ringing in outer space would go unanswered even if an astronaut happened to be floating by, because no one could hear it. Sound vibrations come in a wide range of frequencies. The audio range—which extends up to about 20,000 vibrations per second (cycles per second or CPS)—includes those frequencies that people can hear. Of course, some individuals do hear better than others. Women, in particular, can usually detect noises that are of too high a frequency for men to hear. And most animals exhibit hearing capabilities superior to those of humans. Many insects, for example, can produce and hear frequencies that are beyond our limitations.

When the frequency of a sound extends beyond our normal hearing limit, we have ultrasound. Fig. 1 illustrates the sound frequency range from 0 to 50,000 CPS and shows the hearing capabilities of humans and several animals.

Accelerated Plant Growth

The possibility that plants might respond to sound waves was explored to some extent more than a century ago. Charles Darwin, the famous evolutionary theorist, was convinced that sound could benefit plant growth. He even attempted—without success—to stimulate plant growth with notes from the bassoon and other musical instruments. Similar tests were performed by the eminent German plant physiologist Wilhelm Pfeffer, with the same negative results.

ben king
9/7/2009 5:51:37 AM

use airophonics with the ultra sound this solves the problem. the plant is able to absorb more nutrients I dont recommend using PV as there really is no need as you should be giveing your test plant enough light


egbert
1/19/2008 3:15:42 PM

How difficult would it be to modify this design to produce either 28 or 40 kHZ? There are numerous studies that show the effectiveness of sonic mixing in the production of biodiesel and this design seems like an ideal starting point. The chip will handle the frequencies so the only question is what capacitor is appropriate?






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