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Comment by pixelpoet | Hacker News Reader

I'm fairly sure coffee grounds are the most valuable "waste" that we regularly throw out. Some time ago I found out how obscenely good it is for starting plant growth, and it's great for a million less obvious things too, now even making concrete!

That's extra good because apparently we're running out of high quality sand for making concrete.

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I keep my grounds but I've found whenever I use them on indoor plants it grows mould on it within a day of watering the soil. Outside plants / veg don't have this issue -- have you come across this before? I keep my used grounds in a conservatory, they're very dry when I use them, although I guess not dry enough...

Direct UV light inhibits surface mould growth. This is why you don't see it (as much) outside.

grounds are fantastic in an active composting environment. they make really great, nutrient-rich soil. less so for indoor plants with their tiny, relatively sterile environment. Indoor plants usually suffer from two problem wrt coffee grounds: a "that's going to mould," problem and a "that's too acidic on it's own to be useful," problem.

Thanks, that actually makes a lot of sense. So I've been using them wrong, whoops! I guess I should get myself a little bin to compost stuff in

Mix them with a bit of soil rather than leaving them on top.

How old is your soil? Mixing in some fresh soil with the grounds might be a solution since a lot of the micro-organisms in soil that would break that down and eat the mold degrade over time.

i live in an arid climate and just air-dry and then put them in a container for later use. however i also only use it as part of the soil for outdoor gardens. my grandmother’s “recipe” was topsoil, sheep manure, coffee grounds, and banana peels and that’s worked out for me too

You have to compost first, really.

> apparently we're running out of high quality sand for making concrete.

Sand for concrete is increasingly obtained by crushing of hard rocks like granite (manufactured sand or M-sand); this can have superior properties to the previously used natural concrete sand.

My understanding is that crushed rock is inferior, as it binds too much water that weakens the concrete.

I'm pretty sure this is going to depend on what kind of rock it is, and how it was crushed and screened.

Fuel ("Coffee Logs") and mushroom substrate, just off the top of my head

I live on a 6 acre hobby 'farm' and have had a huge garden in the ground in my own native sandy loam here... but the only good pepper plants I've ever managed to grow were grown in partially composted coffee grinds mixed about 50% with sand... in pots.

But that was when I worked at the Google Waterloo office and could get as much a quantity of grinds as I wanted from the cafe there. Wish I still had access to that. 1 day of grinds was a 5 gallon bucket!

Every coffee shop I've worked at had someone who would come by and pick up the grounds every few days. It was always clearly just some guy who had a never-commented-on-or-explained arrangement with the owner, rather than like a company using it for commercial compost. You might be able to ask around and get a similar thing going?

Also even years later I strongly believe that, somehow, a trash can full of espresso grinds is the heaviest material in the world. Shit's denser than lead idk.

We’ve been able to just call up the local Starbucks’ and usually at least one is happy to give theirs, last time we went 4/4 and got more than we knew what to do with.

Starbucks around Seattle commonly have giant bags of grounds that are free to take. I'd say half the time there's a bag in the basket

https://www-elmundo-es.translate.goog/andalucia/2014/03/01/5...

It's also good for skin exfoliation

Especially if you don't let it cool down first

Wait, you’re telling me that this isn’t how they make iced decaf? Errrr, cold-brew?

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