EARLIER TODAY a member of a gardening list I belong to asked whether coffee grounds are good for the garden and, if so, how to use them. I did a quick google on "+coffee +compost" and hit pay dirt (so to speak). It seems that Sunset magazine (a mag that's big on the West Coast) sent a batch of Starbuck's coffee grounds to a soil lab for testing. The results were so interesting that I thought they would be worth passing along here.
It turns out that coffee grounds are a great soil amendment, though they might tend to acidify your soil slightly. (They are about 6.2 on the pH scale.) They can be mixed directly with soil at a rate of about 1 part coffee grounds to 4 parts soil (to a maximum of 38% coffee grounds by volume), or they can be sprinkled on the surface of the soil where they will behave something like a mild, slow-release fertilizer.
1. The N/K/P balance of coffee grounds is 2.28%, .06%, .6%
2. Coffee grounds do not supply appreciable amounts of calcium, zinc, manganese, and iron
3. They do supply useful amounts of copper, magnesium, potassium, and phosphorus. The potassium and magnesium become available almost immediately.
4. Coffee grounds do not supply large amounts of nitrogen. However, as soil organisms break down the grounds they do release small amounts of nitrogen and other essential elements. In effect, this makes coffee grounds an excellent slow-release fertilizer. (And a lot cheaper than Osmocote!)
The full article is at http://www.sunset.com/sunset/garden/edible/article/0,20633,1208232,00.html.
By the way, don't forget to buy shade-grown coffee, which preserves habitat for birds and other animals. For details see http://nationalzoo.si.edu/ConservationAndScience/MigratoryBirds/Coffee/