It's theoretically possible, but it reminds me of the saying that in theory there's no difference between theory and reality, but in reality there is.

If my math is correct, it would take a little more than a ton of coffee grounds to provide 3 lbs of N per 1000 sq ft. I think that's the recommended amount of N over the course of the season for a KBG lawn. That's not the amount that would be too much for the lawn. That's the amount that would be about right.

Here's the math I used:
.25 acres = 10 890 sq feet
10.89 * 3 = 32.67 (to get 3 lbs for each 1000 sq ft)
32.67 / .015 = 2178 (coffee grounds are about 1.5% N).

If one of the silver bags holds 5 lbs of grounds, you'd need more than 400 of them. If you stopped every week (winter and summer), you'd have to average getting a little more than 8 bags a week to get enough to provide the recommended amount of N for your lawn.

It would be more possible to APPLY too much at one time. If you stockpiled the grounds and applied them more than about 1/4 inch thick and let them dry out, they could repel water. I think they'd also make it tough for the grass to push through if they're applied more than about 1/4 inch thick.

I can second the fact of grass having a hard time going through the too thick layer of coffee grounds. I use coffee grounds (and tshirt shreds, shredded paper, etc) to fill n when my yard makes its summer cracks. ;) The best way to fight this for my small yard is to rake the grounds out over the yard so they form a thin layer. I'm not certan what to tell you over such a large area wth acreage.

Good luck!
Christina

BP, it seems your calculations are based upon the protein content of coffee grounds. I've been searching for that info this morning but have yet to find it. As far as the quantity of grounds, I can get far more than 8 bags per week. There are more than that in the back of my truck right now. I'm going dumpster-diving to get as many plastic bags of this "black gold" that I can reach!!

I guess the bigger question is this. If I keep flinging the coffee grounds every week in such large quantities, will there be any detriment effect? The intent is not to have a layer so thick you can walk across it, but there has to be a point at which there is no benefit.

I based them on 1.5% N, which is just a figure I read someplace. I've actually seen ranges from 1.5% to 2.5%.

Since you can get a lot of grounds, you could get to the point where you're getting too many. I don't think you need to worry about getting too much N from them. The more likely problem would be that they wouldn't be breaking down as fast as you're applying them. Then they could start to accumulate and get too thick. I don't think it'll be a problem until the grounds start to accumulate.

On your size lawn I do not think its possible to put too much. I've been using the UCG's on my front lawn which is about 1800sq ft and could see over doing it. But at your lawn size, you would have to be trucking the stuff in to accumulate a thick coating.

How are you putting this stuff down? UCG's are a great free way to give a small amount of fertilizer, or in my case a free topsoil to help some erosion on a small lawn or garden. But that's a lot of effort if you're doing this by hand on such a large yard...IMO of course...

As a practical matter, you won't be able to overdose a large area with coffee grounds if you apply them uniformly. The more organic matter you have in the soil, the more microrganisms you will have. The more microbes you have, the more they eat. It really is a self limiting process unless you are dumping in thousands of lbs of material at a time.

And yes, there is a law of diminishing returns. Your plants aren't going to absorb an unlimited amount of nutrients. They will grow faster for a while and up their consumption, but eventually, you will just end up with nutrients leaching out in rainstorms and the like.

Bump,

I was just looking into this, and read that coffee contains "oxalic acid, which binds calcium ions into insoluble compounds your body cannot absorb."

I'm no chemist, but am wondering if coffee would then be expected to impede liming with calcitic limestone?

Here is a link that might be useful: coffee nutrients

OK, so here's a really dunb question...but if the goal is to be earth friendly...will the coffee grounds harm the robins eating earthworms from the lawn? We have tons of them here. I might have to post on the Humane Society forums- HA!

Albanyjen, that reminds me that caffeine can be used as a pesticide, killing slugs and insects at high enough concentrations. I imagine it wreaks havoc on some microbes, and maybe even a lot of beneficial ones, but how many?

However, depending on how the coffee was brewed, a good deal of the caffeine was already consumed, though I'm sure there is still some residual in the grounds. My guess is that this would only be a problem if using large quantities of coffee, but I can't find anything to back that up. So I am reluctant to go crazy with the coffee grounds until I learn more about what they actually do.

There's not much caffeine left in the grounds. Caffeine is water soluble, so most of it ends up in the coffee, not the grounds.

The LD50 of coffee is 192 mg/kg (in rats). If we assume the same for people, and 120 mg per cup of coffee, the LD50 would be somewhere in the neighborhood of 130 cups of coffee for a 180 lb person.

There was a study a few years ago (I think in Hawaii) that found that slugs (maybe it was snails) could be killed with caffeine, but the amount that was used was much more than what would be in a cup of coffee, much less the grounds left over after brewing. Some people have reported that the grounds seem to repel slugs to a certain extent, although there is some thought that the reason could be the texture.

I've noticed a marked increase in the number of worms in my lawn since I've been flinging coffee grounds on it, so I think that if anything, the grounds are beneficial to the worms.

Thanks BP for that information. FWIW the amount of caffeine extracted depends on the method of preparation, but I can believe that generally more ends up in the coffee than remains in the grounds. But the OP was considering using massive amounts of coffee. Do you think that would make a difference? I have no idea how long caffeine (or oxalic acid) persists in the soil, or how it might affect any of the soil microbes. I haven't been able to find any discussion of this.

I guess "massive amounts" depends on interpretation. I calculated that it would take more than a tone of grounds to supply 3 lbs N per 1k sq ft. That's on the low end of what is recommended annually for a typical KBG lawn. I would consider a tone to be a massive amount, and that supplies just enough N. You could easily use half again as much (4.5 lbs N per 1k sq ft) and still be within the range of N for a lawn. That's a LOT of coffee grounds, even when spread over the growing season.

Unless he plans to accumulate them and add them all at once, that's not a very deep layer in any one application. The way I apply grounds is to start at one corner and fling the grounds around until I run out. The next time I get grounds, I pick up where I left off until the entire lawn is covered. Then I start over. By the time I start over, the grounds I put down originally are gone.

As for the residual caffeine and any oxalic acid, I've never seen any adverse effect. I used to grow rhubarb and tossed the leaves either in the compost or on the ground. Rhubarb leaves have enough oxalic acid to be deadly, but the leaves decomposed just fine. If rhubarb leaves don't cause a problem, I can't imagine coffee grounds will.

If you apply enough grounds that they form a layer more than a half inch thick, they can cake up and repel water. If they get that thick, you need to cut back. Otherwise, they're fine.

Thanks bpgreen.

I live in a fairly dry climate, usually about 23 inches a year annual rainfall with fairly low humidity. I picked up quite a bit of the free grounds and used alot of it in my flower beds.

It got hard to get water to soak in. This is with frequent supplemental waterings.

Now, in Tennessee (?) and with a quarter acre, you probably wouldn't have that problem, at least not for a good while.

I would suggest you try the old "moderation in all things" approach until you see how its going to work. Start small and work your way up, so to speak.

My guess is that if you are like most of us, and are putting it out by hand, the worms will soon be able to keep up with your application rate just fine. ;)