coffee grounds as compost

How much coffee grounds would be an ideal mix for a tumbler composter ? Plus using mulched leaves & kitchen leftovers. I am thinking about hitting up the coffee shop next door. Thanks for any help, this will be my first winter garden.:?:

I add about 1-2 cups full twice a month.

Mel recommends that you keep coffee grounds to less than 10% of your compost volume.

If you have excess grounds, put them in a pile on the ground in an out of the way place to act as a worm magnet. Worms loooove grounds. Then put the worms into the composter. That's a disadvantage of composter gizmos-worms can't get in to help.

boffer wrote:Mel recommends that you keep coffee grounds to less than 10% of your compost volume.

If you have excess grounds, put them in a pile on the ground in an out of the way place to act as a worm magnet. Worms loooove grounds. Then put the worms into the composter. That's a disadvantage of composter gizmos-worms can't get in to help.

Oh that's brilliant right there boffer.^^^ Now I know what to do w/the excess grounds.

Thanks for the replies, I may do as boffer suggested and have a coffee bin box working.

Extra coffee grounds can also be used as mulch.

Hi camprn,

So coffee grounds as mulch? Even around trees, bushes, etc? How much/deep? Or would it encourage weeds?

capatl wrote:Hi camprn,

So coffee grounds as mulch? Even around trees, bushes, etc? How much/deep? Or would it encourage weeds?

Yes, the used coffee grounds can be used just about everywhere. Just a light mulch(0.5-1.0") upon the soil is fine, for the vegetable or flower garden. Even less or a bit more if you can get them. They are a great soil conditioner and the earth worms love them. The only reason I could see that it would encourage weeds is that they are a source of nitrogen.

boffer wrote:Mel recommends that you keep coffee grounds to less than 10% of your compost volume.

Thought I'd resurrect an old topic.  I have always been interested in why there is a "limit" or "recommended limit" on the amount of coffee grounds that can be put in compost.  Most "experts" recommend that not more than between 10% and 25% of the compost be coffee grounds, but I have never seen an explanation or study showing where these recommendations come from. Where do they come from?  And, what happens if you exceed their recommended percentages?

I have, on a number of occasions, composted almost pure coffee grounds - almost pure because it had coffee filters and pine pellets for carbon added - and it always resulted in beautifully smelling black compost.  The finished compost was used on garden beds, and never had any adverse effect - not only did the plants love it, but the earthworms loved it as well.

What should have happened because I composted pure coffee grounds?  The biggest problem I ever noticed was that some coffee grounds fell out through the screens of the compost tumbler, but it wasn't much of a loss. Since I have an unlimited supply of coffee grounds, I love finding use for them rather than them going to the landfill.

Thanks for resurrecting this thread.  I have been wanting to ask a few questions concerning the amount of coffee grounds to use for various projects.  But it looks like there is no real answer and no reason why.  But I will ask my questions anyway because I have found a good source of a lot of used coffee grounds.  I can virtually get all I want.  So a few questions if you can answer them or if there is an answer.

Putting coffee grounds directly in SFG raised beds.
Because my growing season is so long and because I plant during 3 seasons, I use a lot of compost and I don't have the energy to make all the compost I need.  In the past I have grown cover/green manure crops to help supplement the compost.  But the cover crops do not grow much during the winter and I start planting in March so they do not get large volume before I turn them under.  This year I am also trying to compost somewhat directly in the beds.  So, in December, in each 4 x 8 bed I added one 5 gallon bucket of used coffee grounds, one 5 gallon bucket of shredded wheat straw and one 5 gallon bucket of chopped green plant (mostly pea plants now).  So, my question is how much coffee grounds and wheat straw should I put in each 4 x 8 bed.  I realize the wheat straw will not be completely composted before I plant in the spring, but I can add extra nitrogen to help things along.  Hopefully the wheat straw will absorb some moisture and help to keep the bed moist during the long hot growing season.  

Putting coffee grounds in the compost pile.
In early December, I made an approximate 3.5 x 3.5 x 3.5 bin using 1/2 inch hardware cloth.  I filled it with approximately 300 gallons of shredded live oak leaves (which take forever to decompose), 20 gallons of coffee grounds, and about 2 gallons of alfalfa pellets.  It reached a high temperature of 120-130*F.   It has already cooled down to 80*F.  I stirred it up to get some oxygen in the pile but it has only heated back up to 100*F.  The leaves are a long way from being composted.  I need to add something to the pile to get it to heat back up to help further compost the leaves.  So, my question is should I just keep adding coffee grounds (and how much) to get the pile cooking again.  The outside temp has been pretty mild so far this winter.  It usually gets down to freezing about once each week but them warms back up again to 50*F.

yolos, to get through and to keep your composting pile composting, you will either need to somehow insulate your pile or build a bigger pile. Here to get though the cold of winter I would need to build a 5' pile+ to compensate for shrinkage as the pile composts. Or get an insulated rotating composter like the one OhioGardener has. I know I said I was going to fabricate an insulating structure for the Black Knight Composter but that will be next year as I do little fabricating during the winter in my unheated garage workshop. I basically cold compost, it takes between a year to two years but I now have a compost pipe line in operation. I am not a big fan of hot composting, I don't mind weeds and use earthworms to suppress soil borne diseases.

I don't think you need to add alfalfa pellets with your coffee grounds to your compost pile. Just adjust ingredients to obtain a 30-1 carbon to nitrogen ratio. If you were incorporating coffee grounds into the top 6"-8" of your garden soil I would add the alfalfa pellets or a different nitrogen source to offset nitrogen draft. Coffee grounds are an excellent slow release nitrogen source.

You can use the coffee grounds as a mulch, less than 1/2". I use coffee grounds to side dress lettuce and spinach. I use them mostly in my worm bins along with pulverized roasted eggshells and kitchen waste. The only word of caution is, "too much of a good thing is not necessarily a good thing". I am trying to find a compete plant mineral analysis of spent coffee grounds but haven't found one yet. I have seen copper listed as one of them and would like to know the amount as copper can be an anti-fungal and certainly don't need that getting near toxic levels.

Here are a few links covering the topic of coffee grounds.

https://s3.wp.wsu.edu/uploads/sites/403/2015/03/coffee-grounds.pdf

https://www.sunset.com/garden/earth-friendly/starbucks-coffee-compost-test

http://cru.cahe.wsu.edu/CEPublications/FS207E/FS207E.pdf

A link to mix your ingredients for composting.

http://compost.css.cornell.edu/chemistry.html

I am going with 10 more gallons of spent coffee grounds as my final answer. I haven't figured in the two gallons of alfalfa pellets.

Yolos, I use coffee grounds year around on my gardens, and have always had good results with them.  This fall I began experimenting with using them to keep cats off of the raised beds, and it has been huge success.  The primary concern about spreading the grounds on top of the ground, which helps keep slugs off the beds, is that you cannot have complete, solid coverage of coffee grounds.  If the coffee grounds solidly cover the soil, they will repel the rain water and not allow it to soak onto the ground. But, as long as their is soil visible within the grounds they will be fine. If you go out with a flashlight to look at the beds on a warn evening, you'll probably see nightcrawlers grabbing coffee grounds to pull into their holes. 

The mixture you mention about putting in the 4'x8' beds - 5 gallon each of coffee grounds, straw and greens - would not be excessive if allowed to decompose over the winter months (Dec to March?) - and I have used more than that with success.  On one of my 4'x8' beds that I did not want a cover crop on it so that I can plant onion sets in  March, I put down a heavy coating - 1" to 2" - of coffee grounds and chopped green plants, and then I turned it under. Then I covered the bed with 4" of straw to protect the soil over the winter.  By March the coffee grounds will be totally consumed by the earthworms & microbes - which turns them into available nitrogen - and the straw protects the soil from erosion and nutrient leaching.

I don't have an open compost pile due to all of the varmints we have, and use enclosed compost tumblers for all of my composting.  But, I do have a 55 gallon drum with the bottom cut out that I collect coffee grounds in over the winter months when I can't add them to the gardens, and it is amazing how "composted" they become over the winter.  Earthworms move up into the drum as soon as I start adding coffee grounds to it, and thoroughly work it over leaving behind a lot of their castings. They not only consume a lot of the coffee grounds, but consume the coffee filters that are in the grounds as well. In the spring I have very fertile compost to sprinkle on the beds, and put in the holes with transplants as I set them out.

This report gives a pretty good analysis of the nutrient & mineral levels in coffee grounds, both raw and brewed:

MAXXAM ANALYTICS Lab Report


One thing to keep in mind, though, is that the lab can only test immediately available nutrients & minerals, not those that are available after processing by microbes, etc.

Thanks Dan and Ohio Gardner.  I read all of your links and I appreciate them.  I guess once the rain ends and I can uncover the pile, I will empty the bin, then add the contents back with some additional coffee grounds and a few left over alfalfa pellets.  I will count the alfalfa pellets as compressed grass when calculating my C:N ratio.  It will come out about 40:1 which isn't too bad (not great but will work).

Here is the compost calculator I used to calculate the C:N ratio.
https://www.klickitatcounty.org/DocumentCenter/View/3523/Compost-Calculator

Looks like the ratio of leaves, green matter, coffee grounds and wheat straw which I dug into my 4x8 raised beds is just about a good C:N ratio but probably could have put about twice that amount into each bed.  Don't know the effect of digging the material into the beds but it should work ok.  I will still add some compost when planting veggies this spring.

Yolos,  I use blood meal if I need to heat up a pile.  You can check out the ratio in the Klickatat calculator.

I have wondered if the coffee grounds are actually consumed by worms and other organisms in only a handful of months.  They are just ground up hard beans.  ??

sanderson wrote:I have wondered if the coffee grounds are actually consumed by worms and other organisms in only a handful of months.  They are just ground up hard beans.  ??

Probably depends on how many worms are in the beds or the compost bin.  My raised beds have a lot of worms in them - if I take a shovelful of soil out of one of the beds, there will be at least a dozen worms in the soil.  But, when I set up 2 new beds last fall and put 12" of wood chips in the bottom of the bin before adding the top 6" of modified MM, there were no worms in the beds 2 months later and coffee grounds I had added to the beds was unconsumed. I expect as the wood chips start decomposing that worms will migrate up into the beds, though.

Saw this interesting short article on feeding coffee grounds to worms:  Coffee-loving Worms

Earthworms actually consume the microbiology that is growing on the coffee grounds and other food wastes and am now wondering how much the coffee grounds change after passing through the intestines of an earthworm. Wondrous things happen to anything that passes through the intestines of an earthworm, agriculturally speaking. They do have a gizzard and need soil to ground up some of their food similar to a chicken. Your garden soil should have somewhere between 10-15 different species of earthworms. It is possible that some soil enhancing benefits might be species specific. It is only possible to identify adult earthworms, as the location of the clitellum is the easiest indicator for identification by counting segments. Dr. Clive Edwards of Ohio State University is one of the premier experts on earthworms and some of his textbooks go for over $200. Someday when I hit the lottery, it is one of the first thing I am buying.

Because of the carbon to nitrogen ratio of coffee, if by itself should compost rather quickly although because of particle size oxygen maybe a limiting factor and may have a slight ammonia smell. I like OhioGardener's idea of a barrel to store but might raise the barrel up on block and plumb a spigot into the bottom. I would like to utilize the leachate. Have used coffee left in the pot diluted but was inconclusive in my buckets because once again my garden secretary stopped taking notes half way through the gardening season.

OhioGardener, thanks for the lab report on coffee grounds.

yolos, This is how I got my answer of 10 more gallons of coffee grounds. 300 gallons of leaves x 60 ( C:N ratio of leaves 30-80) divided by 20 gallons of coffee grounds x 20 (C:N ratio of coffee grounds)   18000/400   to end up with a 30:1 ratio  needed to add 10 gallons of coffee grounds to get 18000/600. The hard part of building a hot compost pile is usually greens are wet and browns are dry, so by weight is out. Volume is better although browns are usually airier but close enough. Composting is an art, so much so that even when I look like I am doing nothing I am still composting.

yolos wrote:Looks like the ratio of leaves, green matter, coffee grounds and wheat straw which I dug into my 4x8 raised beds is just about a good C:N ratio but probably could have put about twice that amount into each bed.  Don't know the effect of digging the material into the beds but it should work ok.  I will still add some compost when planting veggies this spring.

Yolos, here are some helpful suggestions from a study done at Oregon State University some years ago:

Here are some suggestions for using composted grounds in the yard and garden from the OSU Extension compost specialists:

• Mix grounds into soil as an amendment. Make sure to keep them damp. Add some nitrogen fertilizer if you do this, as coffee grounds encourage the growth of microbes in the soil, which use up nitrogen. While microbes are breaking down the grounds, the nitrogen will provide a source of nutrients for your plants.
  
• Spread grounds on the soil surface, then cover them with leaves or bark mulch.
  
• Add grounds to your compost pile, layering one part leaves to one part fresh grass clippings to one part coffee grounds, by volume. Turn once a week. This will be ready in three to six months.
  
• Or, put them in an existing unturned pile. Just make sure to add a high carbon source, such as leaves to balance it.
  
• Grounds may be stored for future use. They may develop molds but these appear to be consumed during the composting process. Or a large plastic bag works for storage as well.
  
• Paper coffee filters may be composted with the grounds.
  

Notes are from this article:  Coffee Grounds Perk up Compost Pile With Nitrogen

This is my current composting setup - which will be this way for the rest of winter.  The large tumbler is not insulated, and is not used during the winter months. The smaller tumbler is insulated and is used to make compost all winter long - it currently has one side full and is finishing the compost, which takes a month; and the other side was just started with kitchen scraps and a neighbors juice pulp, and will be filling over the next month.

The barrel on the left is about one-third full of finished compost, and is just storage until next spring. The barrel between that one and the composters is about three-fourths full of Starbucks coffee grounds, which are a a combination of cold composting and vermicomposting.  Next summer I will use the large tumbler to complete the composting of those grounds so they can be applied to the garden beds.

The small plastic drum on the far right is a temporary storage area for coffee grounds until there is a use for them to spread on the flower beds, add to the compost tumbler, etc.  After picking up 250# of grounds from Starbucks yesterday, this drum is about three-fourths full, but on the next warm day we have a lot of those grounds will be spread on the perennial flower beds.




A side note:  During a recent conversation with a neighbor she brought up about how much juicing she does for her family of four. I asked her what she does with the pulp, and she said she puts it in the garbage disposal. I guess she noticed my gasp when she mentioned the garbage disposal. I couldn't imagine all that good food going into their septic system, and we brought up composting. They don't garden, so don't have any interest in compost. To make a long story short, she is now saving her juicer pulp into a 5 gallon bucket, and brings it over once a week to dump into my tumbler. The next day, that section of the composter will be up to 110°F to 120°F.  She juices primarily carrots, kale, and beets. The finely pulverized pulp composts really fast, and the microbes can't wait to start digesting it.

I'll add this too: JimmyCee (a long-time member) had a space between his compost beds that he filled with only coffee grounds. The worms absolutely LOVED it!

Yes, the do love it, AM!  Next spring when I turn over that drum full of coffee grounds to begin emptying it (I forgot to mention those two drums on the left have had the bottoms cut out, so they are open to the soil), I will find balls of worms in the coffee grounds.

Do you try to save as many of the worm clusters as possible before putting the material  into the tumblers to compost?  When I composted in a big cage, I didn't worry because they would crawl out as it heated.  Now that I use a tumbler fir composting, I only use worm-free materials.

Score on the juicing wastes! 

sanderson wrote:Do you try to save as many of the worm clusters as possible before putting the material  into the tumblers to compost? 

Yes, when I turn over the drum I take as much of the worm castings and the worms as possible and add them to the gardens.  I try not to put any of the worms or their castings in the tumblers - I hate wasting such valuable resources.  I have to be quick, though, because as soon as those worms see daylight they try to retreat back into the ground. 

OhioGardener wrote:Yes, the do love it, AM!  Next spring when I turn over that drum full of coffee grounds to begin emptying it (I forgot to mention those two drums on the left have had the bottoms cut out, so they are open to the soil), I will find balls of worms in the coffee grounds.

"Balls of worms"...... My dream here with our GA red clay....