Gardening Pesticides

Caffeine is Actually an Insecticide

20160805AAA.jpgThe coffee plant (Coffea arabica) didn’t evolve the capacity to produce caffeine just to help humans keep their eyes open through a boring day at work, but rather as an insecticide. En effect, insects that try to eat a coffee plant will quickly be paralyzed by the caffeine and other toxic products it contains and may even die.

Sadly for coffee-drinking gardeners, watering your plants with coffee will not repel insects: caffeine decomposes too quickly to be effective, plus it is also slightly toxic to roots and beneficial soil fungi. Thus you wouldn’t really want to water your plants with coffee.

However, you can put coffee grounds in the compost and later apply it to your plants. Once they have decomposed, coffee grounds are beneficial to plants, enriching the soil in minerals.

Beware, however: despite plenty of claims to the contrary, the coffee grounds are not a miracle product, but simply an organic waste that decomposes over time as do so many others. Read more about it here: The Truth About Coffee Grounds.


Larry Hodgson is one of Canada’s best-known garden communicators. He has notably been editor-in-chief of HousePlant Magazine, Fleurs, Plantes et Jardins, À Fleur de Pot and Houseplant Forum magazines and is currently the garden correspondent for Le Soleil and radio garden commentator for CKIA-FM Radio. He has written for many garden publications in both the United States and Canada, including Canadian Gardening, Harrowsmith, Horticulture, Fine Gardening and Organic Gardening. He also speaks frequently to horticultural groups throughout Canada and the U.S. His book credits include The Garden Lover’s Guide to Canada, Complete Guide to Houseplants, Making the Most of Shade, Perennials for Every Purpose, Annuals for Every Purpose, and Houseplants for Dummies, as well as nearly 60 other titles in English and French. He is a past president of the Garden Writers Association (now Garden Communicators International) and the winner of the prestigious 2006 Garden Media Promoter Award offered by the Perennial Plant Association. He resides in Quebec City, Quebec, Canada.

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