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Coffee grounds: confused if good or bad for soil?

 
pollinator
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I’m now receiving 15kg (30 lbs.) of used coffee grounds free DAILY from a cafe.

I throw it loosely over my new garden beds which are mulched with pine needles. I felt great about it, but then read that contrary to peoples’ anecdotal evidence, coffee grounds are bad for soil. It’s alleopathic and some people say plants grow worse when it’s sprinkled around them. Yet on other sites people say coffee’s amazing for the soil and plants.

What do you think? Unfortunately I can’t just compost it as I don’t have room. Sprinkling it over pine needle and other leaf mulch is the only feasible way for me.
 
pollinator
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No direct experience to share, but I imagine that dose is the issue.  A mulch made solely of coffee grounds would act quite differently from a mixed mulch. Test and see what it does in your conditions.
 
garden master
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I've read that caffeine is a germination inhibitor....might be interesting to experiment with that as it could be useful.

I've never seen issues with coffee grounds and plants, but I've never worked with it at the level you are getting too (I am jealous btw!!!).  One year when I was camping for a week I ran across a beautiful carpet of cranberries growing along the edge of a lake and I cut out a small plug to bring home.  I didn't have any nice soil to pot it up in so I flushed my used coffee grounds several times and then used it to pot up the plug for the 4 days it would take before I was home with it....I now have a nice carpet of cranberries at my house.  May be very plant species dependent, but the cranberries seemed to like it.
 
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coffee grounds can be ideal for growing edible fungi/mushrooms. there are many great educationals on growing oyster shrooms in coffee grounds

heres one

https://www.motherearthnews.com/organic-gardening/cultivating-oyster-mushrooms-on-spent-coffee-grounds-ze0z1905zwoo
 
pollinator
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I think it would depend on how acidic the used grounds are, the pH of the soil, and the activity of the microbiome.

I mean, I know that fresh, unused coffee grounds are acidic enough that if you top an ant hill with them and water them in, the resultant acid coffee will be enough to burn off their little legs, so I imagine that if the grounds are too fresh, only lightly brewed with, that they might negatively affect the microbiome.

But I know it's worm candy. Personally, I would get a worm bin started and process at least some through there. It would also act as a worm breeder, so that when you empty the coffee-grounds-turned-worm-castings out onto your garden beds, some eggs and small worms will go with it, and they will take care of any fresh coffee ground additions.

Honestly, if you just get a tub of red worms and spread them throughout your garden, I am fairly certain that they will process your coffee ground deposits in situ.

-CK
 
Tim Kivi
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Worms dislike acidity, which is why they say not to add citrus peel or onions to a worm farm. But people say worms love coffee grounds, even though they’re also acidic. It puzzles me.

I might keep collecting them for a week and then have a break. I don’t want to unintentionally harm the plants. It’s a shame because this cafe is so happy to have me take the coffee grounds away!

The more websites I’m reading the more I’m finding studies stating coffee grounds inhibit plant growth.
 
pollinator
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Tim Kivi wrote:Worms dislike acidity, which is why they say not to add citrus peel or onions to a worm farm. But people say worms love coffee grounds, even though they’re also acidic. It puzzles me.

I might keep collecting them for a week and then have a break. I don’t want to unintentionally harm the plants. It’s a shame because this cafe is so happy to have me take the coffee grounds away!

The more websites I’m reading the more I’m finding studies stating coffee grounds inhibit plant growth.



If you watch the youtube videos One Yard Revolution, he uses free coffee grounds and leaves to make his compost and has great results.
 
Tim Kivi
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Great i’ll add some to the worm bin!

I’m just going to go full throttle and throw them all over my garden. All my soil is being mulched by a thick layer of pine needles, so maybe the coffee and pine needles mix and help each other. I don’t know.

It’s soooo confusing because there’s strong opinions of pro- and anti- coffee in the garden. Basically the anti-coffee sources say “look we did a test and you can clearly see the plants aren’t growing as well as the neighbouring plants”. Then the pro-coffee people say “my plants look so much better since I started using coffee!”.
 
Chris Kott
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You might be reading too much at this point.

Perhaps you might want to do a limited experiment. I would take the grounds you're using and set up a series of small pots in threes (I have done it in an egg carton), set up controls with potting soil, and plant out a variety of seeds.

The variables I would select would be number of flushes (the number of times you rinse the grounds) and perhaps the ratio of coffee grounds to potting soil.

This will not relate directly to even a large container garden, as even there you have a more active microbiology than you will in small pots of soil on a windowsill.

This will first address the question of retarding germination. If nothing germinates, or if there's better germination and early growth the less coffee in the soil mix, you'll have an idea of the ideal ratio for germination and potting up.

You could go whole-hog, which I think I would do, if I were going to the trouble of doing a scientific experiment and recording everything, making sure that the potting mixture and coffee grounds are both sterilised (I find that microwaving them for a minute or three works a treat), along with washing all the instruments.

In this context, we'd really only be testing if there's any chemical incompatibility, as we'd be removing the microbiological component by sterilisation. I think that in the context of topping up a garden bed with thriving soil microbiology, it's the soil we're feeding; absent the soil life, the grounds are just an organic ground seed material that absorbs water better than sand. I am not certain how bioavailable the nutrient content of the grounds would be to plants trying to grow in dead dirt.

-CK
 
pollinator
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Mixed results may reflect mixed quality.

Organic grounds would be much better than grounds with various chemical residue.

If grounds are not organic, mushroom growing could be good first stage to clean them up.
 
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My opinion - If you don't create a thick layer that can cause a crust and your yard/garden is 1/4 acre or larger and you have plants, grass and trees already growing - you should be fine.

I threw 50 lbs of ucg's on an urban lot the other day and couldn't even tell.  I could have used another 200 lbs to even start to make a difference.

Most of my research states that coffee is acidic and coffee grounds are neutral and Red Worms do quite well with coffee grounds.  

Currently I use ucg frequently and then make "instant" coffee to rinse the buckets out and fling that as well.

My neighbors enjoy watching me.

 
bruce Fine
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coffee grounds can be used to prepare site for blueberry bushes also, blueberry loves acid. coffee loses acidity when used. test ph of it and you will know.
 
gardener
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Tim Kivi wrote:I’m now receiving 15kg (30 lbs.) of used coffee grounds free DAILY from a cafe.

I throw it loosely over my new garden beds which are mulched with pine needles. I felt great about it, but then read that contrary to peoples’ anecdotal evidence, coffee grounds are bad for soil. It’s alleopathic and some people say plants grow worse when it’s sprinkled around them. Yet on other sites people say coffee’s amazing for the soil and plants.

What do you think? Unfortunately I can’t just compost it as I don’t have room. Sprinkling it over pine needle and other leaf mulch is the only feasible way for me.



Spent coffee grounds that have sat around for a week or so, have no allopathy to soils or plants. The bacteria will have had time to break any of those compounds down.
If you are leery of using the grounds, simply leach water through them a couple of gallons will do the trick, then apply as a thin mulch layer (1 inch to 2 inches thick.
Several slime molds love to propagate in spent coffee grounds, these are actually a benefit to your soil microorganism profile.

If you use fresh coffee grounds, these are best for ant control you spread the fresh coffee grounds over the mound and out to about 3 feet away from the mound, water in well once spread.
The acids in the coffee that is brewed this way will burn the ants up and by going far enough away from the obvious mound, you can be fairly certain of getting the queen in the laying chamber as well as the workers and the nursery.

Spent grounds will have some of the acids and caffeine left behind but it isn't enough to worry about for most plants.
The acidity will leach down quickly, usually one watering completes this process on freshly brewed spent grounds.
Worms love SCG, they will grab them and take them underground for consumption.

No coffee sold in the USA has any chemicals in it. This only holds true for fresh ground coffee, not instant types.
There is a file here I wrote many years ago titled "everything you want to know about spent coffee grounds", there is lots of info in that post.

Redhawk
 
pollinator
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Keith Odell wrote:My opinion - If you don't create a thick layer that can cause a crust and your yard/garden is 1/4 acre or larger and you have plants, grass and trees already growing - you should be fine.

I threw 50 lbs of ucg's on an urban lot the other day and couldn't even tell.  I could have used another 200 lbs to even start to make a difference.

Most of my research states that coffee is acidic and coffee grounds are neutral and Red Worms do quite well with coffee grounds.  

Currently I use ucg frequently and then make "instant" coffee to rinse the buckets out and fling that as well.

My neighbors enjoy watching me.



I agree with this. I've probably put 1,000 lbs of used coffee grounds into my 800 square foot garden. The worms love it, and I haven't seen any sign of soil acidification. I discovered that applying it straight onto the soil surface is not good. It dries and forms a water repelling crust. Either use it to make compost first, or work it into the soil surface.
 
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Bryant RedHawk wrote:
There is a file here I wrote many years ago titled "everything you want to know about spent coffee grounds", there is lots of info in that post.



Here’s the link: https://permies.com/t/45126/Coffee-Grounds
 
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I too collect spent grounds from a local cafe and have done so for over 7 years. I garden in a community garden that would have once been a river bed - the soil is no more than a spade's depth. I have been using the grounds to prepare new planting areas by mulching with newspaper, cardboard, coffee grounds and topped with arborist's mulch. I have also put them directly into worm bins and any bags that are left for any length of time become colonised by worms - they love them. I am a total believer in spent grounds, they have really improved the soil. In winter, two of the local ski fields drop off their bags of spent grounds at the gardens - they get put into the compost bins.
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