This is the long and short of how to best use recycled coffee in the garden (coffee snobs will see what I did there😏)
Recently Sam and I bought a heat press to seal bags full of spent coffee grounds. It's created an awesome opportunity to reuse what would otherwise be landfill-destined waste material, and a choice bonus to reuse the bags our coffee comes in as they are sadly non recyclable.
BUT! As a responsible distributor of such a product I felt some research was in order. A lot of information suggests using coffee grounds willy-nilly as a do-it-all equivalent to fertilizer, mulch and pest control. THIS IS INCORRECT!
I think people are quite happy to assume that because it is totally natural, spent coffee will be amazing for all things horticulture. Whilst I sympathise with the appeal that it would be a neat and tidy completion of the circle of life (or one of them, anyway), it just isn't true.
After some digging (#shamelesspun) I've discovered some interesting do's and don'ts.
Here's a summary of how to use spent coffee grounds most effectively to turbo-charge your homegrown goodies (whatever those might be🙃):
1. Coffee grounds are best added to an existing compost heap. Whilst coffee grounds are indeed full of good stuff (mainly nitrogen), there are certain other compounds whose toxicity do no favours for your botanical exploits unless composted first. So despite being indeed a great way to boost nitrogen levels, the toxicity of these other nasties can actually limit nitrogenous bioavailability.
2. Coffee grounds are great in vermiculture. If you have a worm farm, your slender, slippery friends will absolutely love you for it.
3. Coffee can be added to a ready-to-use mulch or fertiliser mix, but shouldn't make up too much more than 10-15% of its total composition lest it be to the detriment suggested above. Using spent coffee as your sole fertilizer will actually cause a significant decrease in overall plant yield.
4. If you are leaving a patch of soil to fallow (restore, restabilise, restructure, etc), spent coffee is an excellent natural pesticide for controlling weeds, insects and vermin.
For further reading, this is a really interesting link of a study conducted if you want to get down and dirty with more science.
Anyway that's all the important stuff! I recommend just go play in the garden and start experimenting with different patches of dirt.
Because plants are awesome!