I don't know if it will rob nitrogen as I have been putting it on my lawn for a couple years now and I have one of the greenest lawns on my court. I also don't have moles anymore but the neighbors all do.
The one thing I do know is you put to much grounds down it will repel water, I have always mixed it lightly into the soil when using it in a garden. Again I don't ever see an issue with the nitrogen in my gardens.

Coffee grounds won't "rob" nitrogen from your soil while decomposing - nor will anything classified as a "green." Things that are "greens" have sufficient (or excess) nitrogen to nourish all of the bacteria that will consume the carbon contained in the material.

I like it better as a topdressing than as a mulch ... when I hear the term "mulch" I think of something that will be put down thickly enough to hold water in and to discourage weeds sprouting through; I think if you put coffee grounds down that thickly they may behave oddly (repelling water as brdldystlu described, or molding). If you're putting it on thinly (1/4 inch? maybe a bit more?) it should not give you trouble in those ways I think.

When any material is put on the soil it is a mulch and that material, whether it has little N or lots of N, will not "rob" the soil of Nitrogen. Where that erroneous concept comes from is when people mix that material inot the soil and the Soil Food Web starts to work on that material using all the available N in the soil to digest what is in the soil.
Coffee grunds, used as a mulch (something laid on the soil), will not "rob" your soil of Nitrogen.

okay, so this is one of the places I saw the info about nitrogen and coffee grounds (link below). I figured they would know what they are talking about...but your experience "in the field" may prove otherwise. At any rate, it appears that any drop in nitrogen in soil is temporary and only if mixed in the soil(?) At any rate, they are a very plentiful additive (thank you Starbucks!) and I'll keep using them...they DO sure heat up a compost bin nicely!

Here is a link that might be useful: Oregon Stae University Extension Service

Two quotes from the above site:

"Coffee grounds are an excellent nitrogen source."

Several paragraphs later:

"Coffee grounds are not a nitrogen fertizer."

It's not fair to use a partial quote like that Robert. The actual quote is;

"Coffee grounds are an excellent nitrogen source for composting."

I think that is a very good article, I'm going to keep that one.

Thx

Lloyd

Lots of folks do not see the distinction between mulching on the surface and tilling or digging material into the soil. A mulch is in contact with the air, and has very little contact with the soil. Any nitrogen deficit in a mulch is made up by drawing nitrogen from the air. Bury it, and the only nitrogen source is the surrounding soil.

Slightly off topic, but I was in a big box store and asked for bags of compost yesterday. The nice lady said I could get it for free from the city, and proceeded to describe a site I know all about where you can get shredded yard waste to use for mulch. I said there's way too much wood in that to dig in as a soil amendment! Sheesh. This was like, the manager of the garden section.

....SNIP.... 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.
....SNIP....Carbon/nitrogen ratio: 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. This means that there is more than sufficient nitrogen present in the coffee grounds to provide for the nitrogen demand of the soil microorganisms as they degrade the organic fraction.

Here is a link that might be useful: Sunset Mag. test of UCG

I liked the link to the OSU brochure. If anyone wants to see it in the future, you might want to save a copy - sadly the Lane County extension will be closed very soon. Other OSU extension offices are doing fine, but IMHO there are a couple parts of the state where people don't seem to realize how rural their counties (and our state) actually are.

Here is a link that might be useful: http://extension.oregonstate.edu/extension/lane/

In my experience, Coffee Grounds will draw in a swarm of earthworms wherever you put them. The worms eat the coffee grounds, and leave worm poop behind.

Worm poop is an excellent fertilizer.

Also, in areas where my heavy clay is especially difficult to break up, the herd of worms coffee grounds draw in do an excellent job of breaking up the soil for me.

If you incorporate coffee grounds into the soil, ie. till them in, then the Soil Food Web will get busy, just as they will with any other type of organic matter, digesting those grounds so you most likely will see a loss of available Nitrogen for a short period of time. If you simply plunk the coffee grounds down onto the soil, do not incorporate, till, them into the soil, the Soil Food Web will not expend large amounts of energy digesting them or working them into the soil so there will be no short term Nitrogen depeletion.
That is also what I read the OSU tract saying.

I'll agree that sprinkling used coffee grounds on the soil attracts earthworms. It's like magic -- add coffee grounds, create earthworms!

I found that adding coffee grounds to the rotten soil in my urban garden did wonders to the soil in terms of tilth and apparent fertility.