Coffee grounds at work

Thursday, June 30, 2011

Coffee grounds and coffee “tea” may be an answer to controlling the deadly cycad scale and mealybugs, warding off grasshoppers and even killing mosquito larvae.

For the past several years, the Internet has been abuzz with stories about the effects of used coffee grounds on cycad scale that devastated ornamental cycads called the queen and king sago. Tom Broome, the newly elected president of The Cycad Society, brought the story to the recent Cycad Day at the garden. Broome, who owns a nursery in Lakeland called The Cycad Jungle, has been publicizing his work with coffee for the last four years, and experimenting on his plants. He uses grounds around the roots of king and queen sago (Cycas circinalis and Cycas revoluta) and he makes a sun coffee to spray on the crowns of the plants.

The cycad scale, introduced into this country in the 1990s, killed the ornamental cycads by the thousands in South Florida. Initially, experts recommended spraying imidacloprid as a spray, along with horticultural oil. But it was soon found that the scale invades cycad roots, and no matter how often the chemical spray/oil combination was used, cycads continued to become infested and gradually weakened and died.

Broome remembers reading an article about caffeine’s lethal effect on insects about five years into the scale scourge, and he set to work. Because coffee plants concentrate alkaloids (caffeine and trigonellin) in their seeds, coffee drinkers get a jolt to the nervous system. Cycads get a jolt to their infestations.

Gradually, Broome said, he worked out a system of making applications of old grounds around the root zone of the cycads in March and July. If he saw scale on the leaves, he used a spray of sun-tea-like coffee made from used grounds.

He has expanded his used of grounds – often recommended as a fertilizer – to keep new bamboo culms free of mealybugs and kill mosquito larvae in the vase of a bromeliad. In all, he told his audience that used coffee grounds will kill scales, mealybugs, aphids, whiteflies and spider mites, and repel grasshoppers and fire ants. And, he said, he made a drip system using a barrel on blocks to automatically water his favorite hot pepper while he goes on vacation. The sun coffee lasts about 10 days and the peppers are free of aphids and grow much larger.

For more information, go to and click on the link to TCS documents.