Organic Material, Ken. Tiffany this is so very true. My daughter's garden in Salt Lake City was nothing but a baked clay wasteland when they moved into their new house in 2007. On top of that (literally) the contractor had spread the excavated subsoil from the foundation over the whole back yard like a layer of icky peanut butter. We 'imported' 25 pickup loads of compost from the landfill there, planted what we could in the top layer, and, as you say, magic happened over the years and the clay became fertile soil as the organic material worked its way down into it. By 2013 when they moved, everything was growing so nicely . . . Now they have a bigger house with lots of (ugghh) lawn and are learning the hard way how beautiful our perennial garden with no grass was. They got dogs, so we planted clover as a groundcover, but again, it improved the soil nicely.

Let's see if I can find 'before and after' pics for you:

I really don't think you could create good soil from our Yazoo clay. You need to look that stuff up and see how it literally destroys houses and highways here.

As a generalization, clay soils are typically high in fertility although it depends on the clay. Clays tend to have high CECs (cation exchange capacity - the ability to hold onto nutrients). I looked up Yazoo clay and according to Mississippi State University:

"The Yazoo Clay is a green to gray calcareous clay of Eocene Age. It is high in montmorillonite clay and reflects near-shore marine deposition (Merrill et al., 1985). The soils developed in the Yazoo Clay are fine textured with a dark gray, clayey surface horizon and a lighter gray subsoil (Dixon and Nash, 1968; Lowe, 1911). Montmorillonite constitutes more than 50% of the noncarbonate clays, resulting in high shrink-swell potentials and cation exchange capacities (Dixon and Nash, 1968). Kaolinite, illite, and vermiculite comprise the remaining portions (Ramathirtha, 1971). ...........These soils have high natural fertility with Ca as the dominant cation."

http://msucares.com/pubs/bulle...

However, you're the one that has to work with the stuff, Ken! Last time I gardened on clay I used to drag wheelbarrow loads from the manure pile behind the barn and empty them onto the garden and the soil became lovely and friable after several years. Where I am now there is shallow sandy loam overlying heavy clay, and that can make drainage quite an issue in some spots.

Back to the coffee grounds. I picked up an abundance of wet coffee grounds from work. When time got the better of me, I tossed it into the freezer. It's been a year and time to think about cleaning out the deep freezer for Hurricane Season. Can I still dump it into my composter??

Yes you can. They don't go bad even when left out to dry

I don't really know the answer but I don't see why not. Even foods kept in the freezer for a year, and not freezer-burned, are fine. In fact, that's where I keep my bags of whole coffee beans, before taking a bag out to use in our coffee grinder. Those beans keep just fine, month after month.

As long is it can decompose, I compost it (with the exception of large thorns, bones, large pieces of wood, & salty kitchen scraps.)

sooby said:... Where I am now there is shallow sandy loam overlying heavy clay, and that can make drainage quite an issue in some spots.

I have a similar situation, but my top layer is very shallow and entirely made-by-hand.

I can manage drainage by visualizing the clay layer as an impervious "floor" under my shallow soil layer and raised/sunken beds. The clay "floor" has to slope uniformly DOWN from any area that I want plants to grow in.

If your overlayer is too thick to shovel or hoe aside while you "shape" the clay floor under it, my method won't help. But I can "slope" the "floor" under a bed to carry water away downslope, or cut a slit trench deeper than the "floor" of a bed, to carry water down and away from that bed.

I think of it like gardening on top of a concrete slab. Anywhere the slab has an un-drained low spot, I can expect water to pool and roots to drown. So I look for the shortest path from that un-drained low spot to some even lower spot, and cut a slit trench to connect the two.

I was surprised to learn that coffee grounds can ever contribute to a temporary Nitrogen deficit.

In the past, I just noted that coffee grounds are "greens" - they contain MORE nitrogen than is needed to decompose them. In a compost heap, they contribute N, they don't consume it.

If I understand your references, they suggest that there is a period of time when microbes can digest the "Carbon" parts of coffee grounds faster than they can extract usable N from the coffee grounds. That surprises me, but what do I know?

It's probably good for a compost heap to have some "slow-release-N" raw materials. That way, less N is lost to the atmosphere since the pile is "running lean" until it gets around to extracting and solublizing any slow-release N.

In the soil, that might not be a good thing, since you never want fungi and bacteria competing with plant roots for a limiting source of N.

I'll probably keep using coffee grounds as a top-dress mulch and scratch them into the surface a little. If a little temporary Nitrogen deficit is happening in the top few inches, I've still lightened the soil, attracted worms, added fast and slow OM, and added more N overall than I've added C.

But the point is well taken: I might NOT be adding as much QUICK Nitrogen as I used to think. Perhaps it is mostly slow-release N.

Maybe a better use would be mixing coffee grounds into a compost heap, or amending clay that mainly needs grit and OM to make it drain and aerated at all.

RickCorey said:

But the point is well taken: I might NOT be adding as much QUICK Nitrogen as I used to think. Perhaps it is mostly slow-release N.

Sunset had some Starbucks coffee grounds analyzed. The NPK analysis of the coffee grounds was 2.28:0.06:0.6.

Quoting from the report:

"Each cubic yard of these coffee grounds contains a total of 10.31 lbs. nitrogen, of which 0.01 lb. (0.09%) are available. Thus, even though available nitrogen is considered deficient in this product, there still remains over 10 lbs. of total nitrogen per cubic yard of coffee grounds. Thus, nitrogen is primarily bound in the organic fraction and is unavailable to plants until soil microorganisms degrade the organic fraction. Through this process, the nitrogen is converted to plant available forms. Over the long term the coffee grounds will act like a slow release fertilizer providing long-term nitrogen input which can then be utilized by plants."

You can read the rest of the report here, it's quite interesting:
http://www.sunset.com/garden/e...

The pH was 6.2, but another article indicated for composting:

"A commonly held assumption states that coffee grounds are acidic, but this does
not hold true experimentally. While two studies on coffee ground composting
reported mildly acidic pHs of 4.6 and 5.26, others have measured neutral (7.7)
to somewhat alkaline (8.4) pH levels. One researcher found that the pH of soil
treated with coffee compost increased after 14 to 21 days of incubation, gradually decreasing thereafter. Obviously the pH of decomposing coffee grounds is not stable and one shouldn’t assume that it will always, or ever, be acidic." This is from Washington State U Extension at Payallup (Dr. Linda Chalker-Scott):
http://puyallup.wsu.edu/~linda...

A while back after I read the above I checked the pH of the coffee grounds straight from our coffee machine and it was 6.8. Decaf though, if that makes a difference!

I have been trying to understand the Japanese study but can not seem to find a definition for meter to the -2. I can find that square meter is defined as meter to to the 2 power but nothing about to the -2. Most recommendations for lawn fertilization are about 1 pound of nitrogen for every 1000 sq. feet per application, 4 apps per year. Since Coffee grounds are about 2% N that would only be about 50 pounds per app. or 200 pounds per 1000 sq. feet per year.

If you look at this page (and I've found several similar):
http://www.gordonengland.co.uk...

scroll down to "electric flux density" and you'll see coulomb per square metre written as C m-2. Above that they use -3 for per cubic metre. So I would say the Japanese study means per square metre, the minus sign indicating per.

The recommendation I have for home lawns here (Ontario) is 2-3 lbs of N per 1000 square feet per year (split into three applications), so not that much different from your figure considering the difference in our growing seasons. It would be much higher for something like sports turf.

Edit: I wonder if for the Sunset analysis the amounts are for dry weight.

Thanks for meter info. I just don't believe wet vs dry could make the difference. At the density,
10 kilo per square meter, I'm not surprised at the results that indicate first year problems.

Maybe coffee grounds got their reputation for acidity when someone piled them up deep, or made a compost heap with lots of coffee grounds.

Those fine grains clog up any air spaces, tending to make a layer or heap anaerobic. That causes fermentation to replace respiration.

That causes the incompletely oxidized fermentation products to be released, and most of those are acidic (or a little toxic, both). In fact, many fermentation products ARE organic acids, like acetic acid / vinegar.

However, the grounds themselves have very little acid after you brew with them! As long as you don't make your compost heap or sheet mulch anaerobic, they should contribute little or no acidity.

10 kilograms per square meter is the same as one gram per square cm. If that is "wet weight", I think the layer would be less than 1 cm deep (less than 0.4 inches). If it was dry weight, I'm guessing it would be around 1 inch deep.

Is that deep enough to go anaerobic? If it is, they should have been raked into the top inch or so of soil, or mixed with coarser mulch.

Wow!! Are you all scientists on this thread?! Interesting information on coffee grounds. Now you got me wondering if coffee grounds are even worth "harvesting"?

YES!

If you want instant-nitrogen, you need to use soluble chemical fertilizers. Everything else takes time to break down.

Usually, gradual-release organic fertilizers are thought to be a good thing.

Mulching with them and composting them work great.

Agree! Coffee grounds are some of the most coveted OM. Particles that small decompose very quickly.

RickCorey said:

10 kilograms per square meter is the same as one gram per square cm. If that is "wet weight", I think the layer would be less than 1 cm deep (less than 0.4 inches). If it was dry weight, I'm guessing it would be around 1 inch deep.

In the Japanese study, the coffee grounds had a moisture content of 65%, so the 10 kg. would have meant 3.5 kg. of actual coffee grounds dry. The one I wasn't sure about was the Starbucks analysis of 2% N, because they said "On the basis of dry matter bulk density (452 lbs. per cubic yard), organic matter content (97.7%) and total nitrogen (2.28%), the estimated carbon/nitrogen ratio is about 24:1." So it sounds like those aspects were measured dry.

IMHO the bottom line is probably that if you are planning on adding a lot of coffee grounds at any one time it is better composted first. Another study on composted coffee grounds compared to other composts noted "The present study also showed that the composted coffee waste that had the highest C/N ratio (21.0) also had the lowest N mineralization degree among all the composts." This is from:
http://scialert.net/fulltext/?...

Another study noted: "......Therefore, the decomposition of the coffee residue is slower than that of other organic materials." That's in this one:
http://www.tandfonline.com/doi...

Cheryl, don't let this put you off using coffee grounds! The only aspect being considered is the length of time before coffee grounds start to release their nitrogen in a form that plants can use, and whether there is competition in the soil between microbes and plants for nitrogen to be used in the conversion process when it is added fresh.

This same question applies to pretty much all organic materials used as nitrogen sources because plants don't, for the most part, take up organic nitrogen. Instead they need soil microbes to convert the organic nitrogen into ammonium (mineralization) and then nitrate (nitrification), which are the forms of nitrogen that the plants can then use. If a material has a lot of carbon in comparison with nitrogen then the microbes will need extra nitrogen to decompose it, which can result in less being available for the plants. This is called immobilization, but it's not permanent, though, as when the microbes die their nitrogen can then be released.

I'm not sure if this helps or makes it sound worse!

To simplify (I'm a notorious over-simplifier, so please correct me if I'm wrong) I would say that you can spread coffee grounds on your lawn, but don't expect them to green it up until maybe mid- to late-summer when the grounds have decomposed enough to release their nitrogen.

If you consistently top dress your lawn and beds with coffee grounds, they will eventually improve your soil and reduce the need for fertilizer. But don't expect immediate results. A better result will be had from spreading on compost made with coffee grounds, but still not a quick result as the nitrogen is slow-release.

I wonder if you started the coffee grounds top dressing in the fall it would compost over the winter (slowly in cold weather) and release when the weather warmed up in the spring?