https://news.oregonstate.edu/n...

CORVALLIS, Ore. – The most consumed drink in the world has more benefits than just keeping us awake. Spent coffee grounds can be used as a soil amendment and compost ingredient, while liquid coffee acts as an effective slug killer.

According to various sources, between 400 billion to 1 trillion cups of coffee are consumed around the world every year. No matter the number, that's a lot of coffee, which means a lot of spent coffee grounds. Using coffee grounds in the garden keeps them out of the waste stream and gives gardeners another option for caring for plants and dealing with slugs.

Linda Brewer, Oregon State University Extension Service soil scientist, said coffee grounds can be worked into the soil or added to a compost pile but should be done with some restraint.

"The big message is that generally people are too enthusiastic," Brewer said. "You really need to take the recommended dosages to heart. I've visited a site where a raised bed was ruined by too much coffee grounds. Like most kitchen waste, it is a fine amendment for the garden, but like anything else, coffee grounds can be overdone."

Contrary to popular belief, it's a myth that coffee grounds are acidic and will lower the pH of the soil. After brewing, the grounds are close to pH neutral, between 6.5 and 6.8. Research shows that whatever change coffee grounds bring to the soil is short-lived, Brewer said. So, don't depend on them to keep a lower soil pH. Some plants like rhododendrons, azaleas, blueberries, gardenias and blue-flowering hydrangeas require a lower soil pH to thrive and coffee grounds won't do that.

Ditto to Urbanwild that soldier flies love coffee grounds.
Re the grounds ruining a raised bed, I would guess it was a drainage issue or nutrient imbalance.

My reply had a lot of autocorrected nonsense. I've fixed that.

Just to make things more complicated...I also get weekly inputs from a kombucha manufacturer, spent grain a few times a year from a local brewworks, and you didn't want to know what I grab during leaf season! 😁

And for you written feeders and compost makers, of you have room for banana trees, grow them. They must have lots of sugars in the trucks and leaves or something because worms LOVE THEM.

It is best to compost the coffee grounds first before using as the bacteria present in the compost pile will break down the grounds and release nitrogen and other nutrients that are present in the grounds. so that your plants can better utilize the nutrients. That makes the grounds more beneficial to the plants it is being used around. I have composted hundreds of pounds of spent coffee grounds over the years to use in my gardens and have not had any issues. Here is a scientific article which may help you in your journey to using coffee grounds in your gardens, https://www.researchgate.net/p...

WIth all due respect to previous commenter and to Dr Linda Chalker Scott-
I'm not buying the requirement that coffee grounds (and everything) has to be officially composted before putting 'in the garden'

. "Nitrogen rich compounds.. break down quickly, releasing plant available nitrogen.." Why not let that happen right around the plants I want to grow?
'..earthworms pull coffee grounds.. into soil.. may account for improvements in soil structure..' Again, why not have that happen right away under my chosen plants?
"Be sure to allow coffee grounds to cool.." Seriously? How hot can my filter full of grounds be by the time I drop it in my compost? (Or are we talking about the WAWA folks dropping 2 pounds of fresh brewed grounds right on their compost bin out back lol)
' .. no more than half an inch.." Has this really been studied experimentally, versus an inch? Probably not, it sounds hard to get a decisive result. Therefore, I feel like that's a guess. So why phrase it like a strict rule? (Because many people want a quick rule, not a long explanation of how to make a judgement call) (It is the strict rules around composting that I rebel against. The world is full of microbes, and the degree to which I can manage them by my actions is, I think, very limited.)

There's what this article says, and there's what Urbanwild reports from real life.

I have been 'composting' for decades. Literally about 50 years. My main goal is to keep organic matter on my land where it supports life, not using gasoline to haul it and bury it in a landfill aka garbage graveyard. If I have lots of dry leaves, then the wet kitchen stuff like grounds may help that get rotting. And Some kitchen waste looks too garbagey to me if I dump it on open garden ground. So I will always set aside a place for it, or bury it.

How anyone handles grounds will in part depend on what daily or 'batch' quantity they have, as well as what type of garden or land they have to play with.

But I'd encourage anyone who can use grounds to do so. And tea bags- but seriously, do not expect miracles from the tiny amount of dried washed leaf matter in each tea bag.

It's a very interesting discussion here.

What I've learned so far is: there's many ways to skin a cat. I have no grounds for complaint.

greenriverfs said: It's a very interesting discussion here.

What I've learned so far is: there's many ways to skin a cat. I have no grounds for complaint.

For what it is worth; In summer I put the coffee/tea bag grounds on/in the compst heap; in winter I dig a deap hole and put the grounds/bags in the hole; in spring I ususally empty the hole and turn the contents into the soil with a rototiller.

I have a cold compost bin, very rarely turned over at all, and every X number of years, will spread it over the garden, and till it in.
Some times I have a pile of items that do not rot very fast and I will dig a large square or rectangle and put the nasty stuff in there and bury it, some times I put the entire pile in there and bury it, then rototill the contents months later.

I not only compost spent coffee grounds (hereafter SCG) in bins, I also trench compost them and spent brew grain in beds when I prep them for winter. I also dump SCG on the surface of almost all of the beds year-round. Not really as mulch but expecting them to be incorporated into the soil by the soil community.

I can't comment much on SCG being detrimental to slugs as I'm not sure about that. In the last 2 years slugs have built up considerably here. Given that I'm already applying large amounts of SCG, if they had a negative impact on slugs I wouldn't expect to see any. This last year almost made me think about justifying a couple of small ducks as slug patrols! Maybe I just need to borrow a couple.

sallyg said:

. "Nitrogen rich compounds.. break down quickly, releasing plant available nitrogen.." Why not let that happen right around the plants I want to grow?

Well you could do that , but you can also do both. Split your bounty of coffee grounds in half and use some around your plants and place the rest in your compost pile(s). That way your compost pile will get some added goodness plus with the grounds being high in Nitrogen, it can speed up the composting process and you could get your finished product sooner.

sallyg said:"Be sure to allow coffee grounds to cool.." Seriously? How hot can my filter full of grounds be by the time I drop it in my compost? (Or are we talking about the WAWA folks dropping 2 pounds of fresh brewed grounds right on their compost bin out back lol)

If you haven't noticed by now, there seems to be an influx of warning labels and other forms of cautions on most everything we come in contact with nowadays. This is just another example of one of them. I teach composting classes in my community and during the pandemic, these classes moved online to reach the large number of new gardeners taking up the gardening hobby . During one of the Q&A sessions at the end of my presentation, a new gardener asked the question, "Do I have to wait for the grounds to cool before I put them in my compost pile?" So yes, I can see why sometimes a warning like this might be necessary.

sallyg said: ' .. no more than half an inch.." Has this really been studied experimentally, versus an inch? Probably not, it sounds hard to get a decisive result.

While I couldn't find any studies done about an appropriate layer of used grounds to lay on the soil, I can take from my own experiences over the past few decades of utilizing grounds in my gardens. I experimented with using grounds as a mulch but found the thicker you apply them one major issue surfaces. The grounds will dry out and become hydrophobic as a crust tends to form on the surface, making it impervious to water. My recommendation would be to keep the thickness of any layer of grounds to a minimum, or be prepared to go through any areas where it is applied thickly and break it up to keep it permeable. ( Side note: I had planned on including that information about not applying the grounds too thickly in my original comment but left it out to keep my response shorter. Seeing your reply made me realize maybe I should have included it originally.)

Thanks for honoring my critical remarks I could have easily caused offense and truly would not want to.
Really, any articles about gardening need to be a jumping off point and folks need to try things and observe. As you did with the grounds getting crusty. It seems obvious to me, but might not to a new gardener, that I'd notice that and correct it.

I still think, if one is running their hot grounds to the compost before drinking that first mug, one really needs to take a chill pill Hey, warm grounds could be GOOD in winter compost!

This is a forkful of compost with a heavy coffee component from November 11, 2023. It's FULL of soldierfly larvae.

It's interesting that discussions about composting so often focus on a single "ingredient." After decades of composting, I no longer have an interest in moving organic matter (OM) more than once. The couple of big piles I've gone to the trouble to make here just turn into ant farms and the ants just eat everything. Not worth doing at all. As OM becomes available, it gets put in the garden somewhere and that is the end of it. Almost always on the surface, but sometimes buried. Sometimes I'll end up with a whole 5-gallon bucket of stuff from cleaning out the 'frige & trimming a bunch of plants. When that happens, I turn the bucket upside-down somewhere and ignore it for a couple of months, usually until I need the bucket for a big load again.

I never think about the individual components/ingredients after I've scattered them somewhere. To compost such minute particles as coffee grounds would yield what - mud? I think it would need to be in some type of container or it would just be lost in the soil under an open ground pile. But I would love to somehow have enough coffee grounds to notice any "effects" of them in particular sometime.

With code grounds I'm after them breaking down as well as being fodder for all the invertebrates and in turn, what they make also goes on. I didn't even drink coffee but if I did, it might not account to a lot. That's why I have an agreement with the local shop and it works for us. It's only 3 blocks away and I just add it to errands rather than make special trips. But, I also get an initially about of eggshells, tree leaves, kombucha SCOBY & kombucha tea leavings, spent brew works grain, plus what we save as waste. The benefit of living urban is that I'm close to all of it and it's easy to work in.

purpleinopp said: After decades of composting, I no longer have an interest in moving organic matter (OM) more than once.

The couple of big piles I've gone to the trouble to make here just turn into ant farms and the ants just eat everything.

Not worth doing at all.

As OM becomes available, it gets put in the garden somewhere and that is the end of it.

Good point...

I gave up on the idea of turning compost after the very first batch...
After reading as much literature as I could stand... Including a huge book on compost from Rodale Press, personal experience suggested that the only legitimate reason for putting in all that work... Saved on gym fees...

At my house, compost is unstoppable...
Doesn't matter what I do...
So... yeah... Best thing is give it to the yard birds... second option?
A decent burial.
Cold composting works too... Just toss it in a pile in the middle of the garden and let it break down on it's own... next year, level pile out, start new pile.
Plant something where the old pile was...