Coffee, Caffeine & Your Plants: Friend or Foe?

Dr. Russell Sharp examines the effects of coffee and tea on plants, explaining how caffeine and other compounds (tannins, organic acids, sugars) can act as low-dose biostimulants but become inhibitory or toxic at higher doses. He covers root drench vs foliar applications, allelopathy, impacts on microbes and pests, and how repeated use can harm photosynthesis, nutrient uptake and root health.

Practical takeaways: occasional small amounts may help rooting, but regularly pouring leftover caffeinated drinks on houseplants can cause overwatering, chemical stress, microbial shifts and long-term damage—so avoid routine use and be cautious if trying coffee grounds as pest deterrents.

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Joanne Chory — Salk Institute (USA)

Mark Estelle — University of California San Diego (USA)

Steve Kay — University of Southern California (USA)

Krishna K. Niyogi — University of California Berkeley (USA)

Bob B. Buchanan — University of California Berkeley (USA)

Chris R. Somerville — University of California Berkeley (USA)

Julin N. Maloof — University of California Davis (USA)

Pamela A. Ronald — University of California Davis (USA)

Daniel J. Kliebenstein — University of California Davis (USA)