[Community_garden] coffee grounds are HIGHLY acidic

[Don Boekelheide]

Hi, Jane, Steve, Mike, coffee discussers,

As I sip my morning brew...

It's hard to find a clear research report on coffee
grounds acidity via quickGoogling, and opinions from
Extension, companies (such as Starbucks) and gardeners
are contradictory. People most often simply repeat a
view they find persuasive, without citing supportive
evidence or independent observations. 

Seems to me there are two main camps - that grounds
are essentially neutral (pH 6.9); or that grounds are
slightly to moderately acidic (roughly in the pH 5
range, somewhere between pH 4 and pH 6, at worst, not
much different than peat moss as one emaven put it).

(Techie point - since the pH scale is logarithmic, a
lemon at pH 2.5 is 1000 times more acidic than coffee
grounds at about pH 5.5).

Interestingly, Starbucks has printed info with both
perspectives. In addition to the note Jane passed
along, they also (in another guide) suggest adding 1 T
of lime to 5 lbs of grounds to neutralize acidity.

I admit I have not tested the pH of local grounds
myself. I need to do that - should be pretty easy. My
guess is that pH of grounds probably varies by coffee
variety, roast (less roast, lower pH??? hypothesis),
brewing and age/freshness.

Anyway, bottom line, Sunset Magazine (I've always
liked them) sent a bag of Starbucks grounds to a legit
lab, which found the pH 6.2 (slightly acidic, in a
good range for most veggies). The report also measured
N (2.28%),P , K (0.6%) and micronutrients (it is a
good N source).

See
www.sunset.com/sunset/garden/edible/article/0,20633,1208232,00.html

I personally use coffee grounds in compost and as a
topdressing/mulch material, hoed in lightly, around
acid lovers like azaleas, hollies and blueberries.
Seems silly now - my *$#@ red clay is more acidic than
that anyway! I can just scatter it where I want, I
guess.

All this does raise a good question about my failed
experiment using coffee grounds as feedstock for
worms. Evidently, acidity was probably not the main
culprit, as I'd assumed. Hmmm. Thanks for getting me
to rethink and reexamine that.

Now, another hit of my java...from a finca in
Huehuetenango, Guatemala - wonderful place to learn
Spanish, but that's another story.

Don Boekelheide
Charlotte NC