Question
Is it good to put coffee grounds around any plants. I've heard it is but don't know which ones like it.

Answer
You'll read from time to time advice that Coffee Grounds are an excellent source of organic matter and make a great mulch.  However, the scientific jury is still out on this.  And I'll tell you why after I give you the good news.

And there is no shortage of good news.  In fact, I've been using them myself -- while trying to determine whether or not this is a good or bad idea.

The organic matter part is true.  They are superb, in fact, as a source of Carbon and Nitrogen.  Although fresh coffee has a pH between 5.0 and 5.5, They are not terribly acidic, because by the time they reach the garden, so much water has been poured thru them, the acid is largely diluted.  The pH of a cup of Starbucks Ethiopian Black Coffee is around 6.3.  The Coffee GROUNDS are close to neutral, with a pH around 6.7.

Neutral pH is 7.

Popular science says that the Coffee leaches out of the used grounds and most of the acid goes with it.  They are only slightly acidic, and the pH is ideal for most plants.

What I love about them is that Earthworms go for Coffee Grounds like bees to honey.  And Earthworms are organic matter powerhouses, turning straw into gold, silt into humic acid laden treasure chests.  Everything is coming up Roses, it seems, for the Coffee Grounds movement.  Starbucks spent one summer stocking its stores with free bags of used grounds.  They stopped because of lack of interest.

Now, with all that, what's not to like about Goffee Grounds?

Well, I still have a question about the potential negative effects -- POTENTIAL -- of the thousands of volatile chemical compounds, including a chemical called FFT (known as "2-furylmethiol" to scientists), that makes coffee smell so good.

There is evidence that acidic environments are hostile to Nitrogen-fixing bacteria. But we do know that compounds released by the roots of Coffee plants are so effective at warding off competitors, Coffee plants can't be grown by their growers without inhibiting the growth of other plants nearby -- including Other Coffee plants.  Weird, huh?

Trouble is, no one has actually decided this should be tested.  Know thy enemy.  Meantime, we have to guess.

Back at the ranch, you should be aware that Coffee Grounds are ALSO great at forming impenetrable barries to Slugs.  That was all I needed to hear to vote for it myself.  Only Garter Snakes do a better job.  Slugs cannot stand Coffee Grounds.

Here's what I would do.

Go ahead and use the Grounds.  But be diligent about checking for side effects.  If the plant is incompatable with the Coffee Grounds, you'll know.  And you can do something about it.  If not, nothing lost.  In the end, I suspect it would be a rare plant that was not pleased as punch with your decision to use these.  But I also happen to take science very seriously, and until those guys at Univ of Calif at Davis or Rutgers do a real analysis and put it in writing, I just don't know. No one does.

Thanks for writing.

THE LONG ISLAND GARDNEER