I put them in my tomato beds this summer, with other fertilisers and new soil mix, so I can’t say if it’s useful for the bed or not. I do see plants are more productive. I will test them with the strawberries in pot, put in a few plants and not in others, to see if there are any real difference.
Do you use them for your vegetables and fruit trees? Yes or no according to your experience?
So I had a look at the scientific literature, and frankly I kicked myself. Coffeegrounds are of course a rich source of caffeine – in fact they can be richer than coffee itself, depending on brewing technique. One of the key functions of caffeine in the plants that produce it is allelopathy – the ability to reduce competition from surrounding species by suppressing their growth. Caffeine is packed into coffee seeds for the very function of suppressing the germination of other seeds.
There is a stack of studies to suggest it also stalls root growth in young plants, preventing their uptake of water and nutrients. Yet others have shown it has antibacterial effects (so much for boosting soil bacteria). And guess what? It isn’t even always very acidic. OK, its effects have varied widely depending on plant species, but it’s never shown colossal benefits that could outweigh the risks.