Question
I read in one of your answers a suggestion of applying coffee grounds to the lawn to assist in attratcting earthworms...and eventually breaking up clay/compacted soil.

Will the high level of acid hurth the lawn if you apply it to the entire lawn?

I have a highly compacted/slightly caly top layer that I need to break up...

I intend to core aerate (3rd time this year) overseed and tehn apply food scrap/waste compost as a top layer.

Would you reccomend the coffee grounds before I do all of this as a way to get th little fellas into the ground?

Answer
Good question, Jeff.  I asked it myself.

And to tell you the truth, when I first applied coffee grounds to my lawn - just a little - I noticed mushrooms appearing a few weeks later as the soil acidified.

Scientific wisdom claims that used coffee grounds do not measure the same acidity as unused coffee grounds.  Please tell me Jeff you are USING these coffee grounds before you put them on the grass... Please!

You never know, with these AllExperts questions, if people really understand the letter of the explanation.

It seemed clear to me that mushrooms were responding in a very positive way to the coffee grounds I had added.  I have lots of earthworms.  My grass was not too happy.  So I just applied pelletized Lime and some backyard compost and the lawn was much happier.

Earthworms do love coffee -- and they love compost even more.  A high level of organic matter is the only way to cultivate a healthy number of Earthworms.  Over-tilling (working your soil until it's as fine as talcum powder), especially when the soil is damp or wet, destroys your soil structure and is deadly to the microbial population.  

Chemicals - well, hopefully the thought of applying those has not even crossed your mind, because you will completely destroy all life in your soil and you can kiss a great lawn goodbye.  Besides, Earthworms hate them.

Earthworms most enjoy feasting on microbes that live in healthy soil.  One scientist calls Earthworms "the largest contributors to soil fauna biomass and key players in organic matter decomposition and soil macropore development."

Compost tea is a concentrate of microbes that Earthworms adore; dosing your turf with compost tea will speed up any decomposition of microbe-friendly things like dead leaves, grass clippings (organic only), coffee grounds, manure and humus.  The more microbes, the happier the Earthworms.

One thing you can count on Earthworms for is gentle, thorough, deep soil aeration.  You have already aerated once, perhaps twice this year.  Although I understand your intention is to break up the compacted soil, you risk killing Earthworms under that soil, and you are not really solving the compaction problem because you are disturbing the soil structure even with a little aeration - sort of like a mini-tilling.  A little patience is needed for this project.  I hate to sound religious about it, but it's one of those things that's going to be done in God's time.  Or, to use that old gardener's saying, All good things come to those who wait.

Keep the Earthworms happy.  Take your mulching seriously (and it sounds like you are quite serious about that, as you have given all this a great deal of thought).  Watch the pH (you don't want your soil pH lower than 6.5, which is the perfect pH for grass).  

If you have grubs, avoid the stuff at Home Depot called "grub killer" and go instead for the Milky Spore Disease which I can tell you is worth the wait.  The power of the Earthworms is astonishing.  The Rancho Mondo website (www.ranchomondo.com/compost/earthwrm.htm) posts the real life data: Earthworm castings hold "5 times the nitrate, 7 times the available phosphorus, 11 times the potassium, 3 times the exchangeable magnesium, and 1 1/2 times the calcium that occurs in the top 6 inches of uneaten soil."  

And as far as aeration, they note: "The aerating tunnels greatly increase the air capacity of the soil (in some cases increasing 60-75%)."

Organic fertilizers are slower acting, but they don't promot thatch and they don't interfere with the Earthworm population.  To quote one of my favorite websites, the Yardener, "A well-managed soil rich in organic matter can easily support 25 worms per cubic foot."  

Just imagine all those wiggly worms moving up and down through your soil, Jeff, diving through the dirt, gobbling up fungi and microbes and creating superrich castings - aerating is for the chemically dependent, not the intelligent gardener.

By the way, I try to hand dig Dandelions, and I don't hate them too much because they break up soil with those tap roots.  

Besides, biodiversity is always a good thing - just so long as they don't go to seed.

Coffee grounds are a wonderful way to mulch slug-magnets like Lilies, Dahlias, Hostas and spring bulbs.  I have also tried them on tomatoes and strawberries, but believe it or not, the fruit begins to taste like coffee.  So for those, I may have to wait for the predatory slug-slugging nematode from Europe, Phasmarhabditis hermaphrodita.

The coffee-mulched flowers, however, are growing beautifully.  Left on the soil surface, the grounds on the ground are a physical barrier around the stems, the most effective barrier I have ever used.  

I have also tried diatomacious earth.  But unlike diatomacious earth, coffee grounds do not have to be reapplied after it rains.  They're free, I don't have to worry about breathing the dust, and they acidify soil that acid-preferring perennials and bulbs prefer.

Grass is a little different.  Slugs moving through the grass are not devouring flower petals and fruit.  They help decompose Organic matter, especially leaves and grass.  Still, they will not like the coffee.  

Earthworms, for reasons that have not yet been explained to me, are crazy about them.  

Starbucks will give them to you by the trashcan-full.  If anyone chuckles, remember that inside they are wondering what you know that they don't.

It's hard, being the smart one.

So the answer is Yes, Jeff.  I think you should apply coffee grounds all over the top of your soil and to soften the pH, apply a layer of pelletized lime, which together will gently improve your soil and adjust the turf environment to make all those wonderful creatures very, very content.  On top, your layer of perfect grass.  Now, that's a match made in Heaven.

Good luck.  Thanks for writing!