Here is the comment, so you can link to your own thread, but it is directed primarily toward the use of coffee and tea as a "tonic" for containerized plants. The use of coffee grounds in compost, as a mulch, or even incorporated in mineral (garden) soils would be less of a problem than the actual coffee or tea, which would contain far more of the potentially harmful compounds.

Forum discussions frequently center on the question of adding dilute coffee/tea to plants as a 'tonic', but Arabica (coffee) and Camellia (tea) are known for their toxic alkaloid (caffeine) content and their allelopathic affect on plants as well as autotoxic (to their own seedlings) effects on future generations. Caffeine interferes with root development by impairing protein metabolism. This affects activity of an important bio-compound (PPO) and lignification (the process of becoming woody), crucial steps for root formation.
We also know that the tannins in both coffee and tea are known allelopaths (growth inhibitors). There are ongoing experiments to develop herbicides using extracts from both coffee and tea that cause me to want to say they might serve better as a nonselective herbicide than as a tonic. I would not use either on my plants; nor would I add tea bags/coffee grounds to my container soils.

Al

Thank you very much! I will share this information with my friends on the Florida Forum in the interests of being a bit better informed. I know many of them collect bags of used coffee grounds from Starbucks and other places, and this might impact how they decide to use them.

I appreciate your help!

Marcia

For those of us who did not see this the first time, thanks for bringing it back up!