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I've read that spent coffee grounds work well as a fertilizer. But the methods of application are all over the map. Some indicate using it in compost, others suggest spreading it and broken eggshells as an insect deterrent, and others recommend making a "tea" (heh!) out of it to water plants. Personally I've just taken my coffee filter outside to clean it and hoped for the best.

Is there any particular reason to pick one application method over the rest or should I just do what's easiest?

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I dump mine in the kitchen compost bucket simply because it's the easiest thing to do... –  bstpierre Jun 22 '11 at 1:04
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@bstpierre I used to do this but with a compost barrel and a cafetiere/french press, a lot of liquid would go in as well - it adds up and results in compost that is too wet (and hence anoxic/anerobic). This year I've been putting much more of it directly on the pepper beds. No pest problems. It will eventually break down, the water does some immediate good (a cool day today: 95F!), and other answerers here say the acidity is good for the peppers. –  winwaed Jun 22 '11 at 2:52
    
@bstpierre +1 for your above comment, as that's exactly what I do. But to address "winwaed's" comment/observation, I do allow the used coffee to dry-out for a few hours before putting it in our indoor counter top kitchen compost bin. –  Mike Perry Jul 27 '11 at 16:32
    
I have used coffee grounds in my veg garden regularly for a long time now and think its a great idea. So far based on everything I have read most vegetables prefer a slightly acidic soil and thats what coffee grounds does to the soil. I am currently trying out coffee grounds on my lawn, still in the process so nothing to report yet. You can check out my veg and lawn pics at www.projectgreenbean.com –  user1449 Jul 21 '12 at 2:42
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9 Answers 9

up vote 23 down vote accepted

EDIT:

Here is a nice article from sciencedaily.com that talks about the benefits of adding coffee grounds to your compost pile. Some excerpts:

  1. On the general benifit of coffee grounds.

    Coffee grounds can be an excellent addition to a compost pile. The grounds are relatively rich in nitrogen, providing bacteria the energy they need to turn organic matter into compost.

  2. On adding them directly to the soil.

    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

  3. On composting it.

    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.

  4. It also advises against adding uncomposted grounds near plants.

    ... uncomposted coffee grounds are NOT a nitrogen fertilizer... Germination tests in Eugene showed that uncomposted coffee grounds, added to soil as about one-fourth the volume, showed poor germination and stunted growth in lettuce seed. Therefore, they need to be composted before using near plants.


The method you choose depends on how much coffee you drink (i.e., how much coffee grounds you generate) and how much time & patience you have.

Composted coffee grounds are probably the best, as they provide a good source of nitrogen and mildly acidic soil. However, if you don't want to get involved in composting, I think you'll be fine putting coffee grounds directly in the soil and mixing it slightly. It probably might take a little longer to break down on its own, but it'll be ok. Coffee "tea" is also one way of doing it, but I think it's more of a diluted one-time fertilizer drink for the plant. You don't get the same benefit as having the coffee grounds in the soil, which dissolve a little bit of nutrients each day and encourage growth of microbes.

Coffee grounds are great for plants that like slightly acidic soil like tomatoes and blueberries. They're also good for azaleas, if you grow them (I found this out just today, when I read the contents of an azalea special fertilizer mix). I don't drink coffee myself, but I go to the local starbucks and get a bagful of used coffee grounds which I then use as fertilizer for the above plants in my garden.

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A related link: sunset.com/garden/earth-friendly/… –  Lorem Ipsum Jun 22 '11 at 4:25
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This is the sort of information I was looking for. The Sunset article had lots of good information too. –  Jon Ericson Jun 22 '11 at 20:38
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Following up rsghoheen's answer, I checked what Starbucks themselves say. They have a full blown scheme called "Grounds to Gardeners".

OK, so you don't need Starbucks because you've got your own grounds, but check out what they say...

The instructions they print on the side of their packaged used grounds are:

Coffee grounds are a nutritional additive for your soil. During the brewing 
process most of the acidity is removed, leaving used groudns with an 
average ph of 6.9 and a carbon-nitrogen ratio of 20-1

Directions:

Add grounds directly to your garden
-----------------------------------
Apply this “green” material as a side dressing to nitrogen loving
plants, including most perennials and allium plants.
Balance the nutrition of your soil with “brown” materials such as leaves
or dried grass.

Or to your compost
------------------
Combine with “brown” materials in your compost pile.
Use grounds within 2-3 weeks of brewing to capture the most
nutritional value.

More info here and here.

enter image description here

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One thing to avoid is using coffee grounds inside where there is a risk of mold growth (as there would be if you left the grounds in your pot for a week)

Likewise, I would avoid using coffee grounds with potted houseplants, not only because of the potential for fungal growth but also potential buildup of soluble salts.

-B. Rosie Lerner (Extension Consumer Horticulturist Purdue University)

http://www.hort.purdue.edu/ext/groundsforgardening.html

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An excellent article. I think I'll stick to using it on the outside plants as suggested. –  Jon Ericson Jun 22 '11 at 20:40
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I've known a person or two who swears by mixing (relatively small amounts) of coffee grounds directly into the soil around azaleas. All I can say is, at least, it doesn't seem to cause any problems. Coffee grounds, as far as waste food goes, is already pretty far broken down (a roasted bean, ground up and boiled). As others have already pointed out, you could risk attracting unwanted pests, but taking small amounts and mixing it well with the soils should minimize that risk (I can confirm this in Seattle and London -- your mileage may vary).

However, I'd vote for placing it the compost bin. It makes for a great addition to the compost bin because of the small, easy to digest particles. If you use a paper filter, you can drop the whole thing in.

I'd also make a pitch to go to your local coffee shop and see what they do with their used grounds. Many Starbucks and independent shops package up the grounds to be picked up by people wanting it for compost, and others I have visited will gladly package it up for you if you ask. They have someone haul away their waste, and you get a great addition for your compost bin. That's a win-win. The only problem I've ever had is that most of the coffee shops in my neighborhood were usually stripped clean by other gardeners by the time I got there.

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I make French Press coffee every morning. I have gardens just outside of the back door near the kitchen. I rinse the grounds directly into the gardens. The grounds gradually decay. There is no unpleasant odor or problem.

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I have a tray in my kitchen lined with several newspaper sections. I dump out my coffee grounds & filters on it each day. The paper helps them dry out. When dry I transfer it to a bowl and collect it until I feel like using it. If I have a worm bin I put the whole mess in it once the grounds are cool and no longer sopping wet. Anyway, drying the grounds makes it easier to broadcast over a bed or the grass. Also, you can brush grounds off the plants if they are dry, too. Grounds help in several ways:

  1. I can't vouch for this, but dogs and slugs are not supposed to care for them
  2. They are a good source of nitrogen
  3. This source of N is tied up, though and requires microbes to make it usable, so coffee brings in microbes and improves your soil's health.
  4. Coffee is loved by worms- they will aerate the soil and turn the coffee into worm castings, a very good fertilizer.
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I have been using grounds as top dressing for tomatoes, garlic, onions, blueberries, roses, hibiscus, iris, strawberries, and evergreens for years, with great results.

I use a "tea" of 1 coffee can-full (2lb can) of dry grounds in 5 gallons of water. I mix it Tuesday night, let it sit in the sunny backyard until Saturday, then strain it into my sprayer & give all the trees & flowers a heavy misting Saturday and Sunday afternoon, when the air temp is in the 70-80°F range. I also use this on the indoor flowers, and have no problem with them. It seems to perk the plants up, especially the apple and nectarine trees. Grandma said it was the caffeine, and I learned long ago that Grandma was usually right.

I put equal amounts of grounds, dry leaves, and grass clippings on top of the worm bed, and they tend to disappear very quickly. We have both Georgia Reds and 'Crawlers in the bed, and they both seem to be very healthy.

Every six weeks or so, I spread grounds on the grass (Scott's Drop-Spreader on #3), and I've noticed the grass seems to grow somewhat faster for the next month or so. It may be due to the grounds' properties, the increased worm activity, or maybe both.

Interested in others' findings.

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Dumping any food in your garden sounds like a good idea at first, but the pitfall is that we must process the food before using it as a fertilizer. For the food is not decomposted into the simplest form, thus various bugs such as Springtail which eat decaying matter. This is the reason why we need composting instead of dumping the food right in your field.

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Although good general advice (I wouldn't want to put veg peelings or apple cores on the garden - they'd also attract rats and our dog!), coffee grounds do not appear to have this problem. –  winwaed Jun 22 '11 at 2:50
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Once my mum try to convince me dumping egg shell into the soil is good, but my soil end up becoming a nest of springtails.... –  lamwaiman1988 Jun 22 '11 at 2:52
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Perhaps there was egg still on the shells, or the membranes attracted them? I would imagine egg attracting insects, but not the actual shell itself if it is clean. –  winwaed Jun 22 '11 at 2:54
    
One might think protein in the remaining egg is good for the plant....so... –  lamwaiman1988 Jun 22 '11 at 3:03
    
Coffee grounds do not offer much nutritional sustenance for insects or animals. They do improve the consistency of the soil. –  ncmathsadist Jul 11 '11 at 0:27
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I add my coffee grounds to my worm bin... It is an easy way to process veggie scraps, and a lot faster than composting (at least in the semi arid salt lake valley.)

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