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.

Merry Christmas.

Al

Interesting biochemical notes. Maybe the answer is to leave coffee and tea together in containers so that the rain can leach out the harmful chemicals for a year or two.

The prospect of abetting "soil collapse" by adding loose organic matter in containers is expertly discussed at length elsewhere in this forum, by others.
Determined recyclers of coffee grounds & tea could add it to a vermiculture box; worms love that stuff, going at it without delay.
Take worm's castings & make yourself an aerobic extract (a.k.a. worm tea: use a bucket with external aquarium air pump driving submerged air stone in bottom of the water & another air stone inside the floating castings' sac).
After bubbling up your fresh brew filter the tea out, dilute & use that to "water weakly" (to quote an other). You will get fertilization, plant growth hormones & interesting micro-organisms; a more container appropriate end use of organic matter. (I give the leftover sludge back to the worms.)