I routinely add coffee grounds and teabags to the compost that I put in my wormery. What effect, if any, would residual caffeine have on earthworms and other invertebrates?
• We live in the country and have an aerobic sewage treatment system that depends on worms. Our suppliers advised us not to put coffee grounds in because the worms don’t like it. Since these animals are such a mission-critical component, we have scrupulously followed this advice.
A relative with a simple compost system – like that of your correspondent – reports that by gradually increasing the dose, he has got his worms to tolerate caffeine, but we still won’t risk it with our sewage.
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Guy Cox, St Albans, New South Wales, Australia
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