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Comment by krunck | Hacker News Reader

Coffee grounds make a great fertilizer - a far less energy intensive use than charing for use in concrete.

When I worked at a coffee shop, a lot of people would come in for our "fertilizer". We would save it in buckets for people to take.

One time as a lark my partner grabbed a bag from one of those buckets in Seattle and then flew it back to Colorado with her. Probably in that case it would've been more practical to just make concrete out of it, but it was fun to add to the compost pile.

Did they have to rebag or double bag it? I've seen some of those tear in transit, quite the scene haha

It's also good material for composting and vermicomposting. Relatively regular grain size probably makes it a decent source for home biochar (definitely better than wood if you're just looking to add high-surface-area microbe housing to your soil). Given that coffee is so popular around the world, I think there could be real benefits to using it as a building material if it can lessen the need for new concrete.

I've been emptying mine at the base of our sapling laurels for about 18 months. I think the ones where I'm emptying are very slightly fuller looking than the others. Hard to say though.

Coffee waste is acidic which is not good for all plants.

It is not particularly acidic, most of the acidity in coffee grounds ends up in your coffee. Even if it were more acidic, changing the soil ph would require so much that you probably wouldn't worry about it unless you ran a cafe and used all the waste on your garden.

I'm using my experience of trying to maintain more acidic soil around my blueberry bushes, and all the coffee bean waste from my kitchen wouldn't make a difference even if it was very acidic (which it isn't).

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