[Community_garden] Lime, worms and flies

[yarrow at sfo.com]

Don wrote:
>Interestingly, coffee grounds would do the opposite of
>lime chemically, making conditions too acidic. But
>worms don't like them, either - I did an experimental
>trial of large amounts of coffeegrounds as sole
>foodstock, with newspaper as bedding, in wormbins, and
>the results were a complete bust (small amounts of
>grounds are fine).

Acidic coffee grounds? That's a common myth. In fact, although coffee 
itself is acidic, used coffee grounds are neutral.

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http://faq.gardenweb.com/faq/lists/soil/2002015354019975.html

While it is widely thought that they are acidic it has been shown 
that most of this acidity is removed in the brewing process. Used 
grounds are essentialy neutral and composting them with other 
materials will buffer any minor residual acidity.

One of the forum regulars with a scientific background did some 
controlled chemistry experiments on the acidity question and this is 
what he had to say:

"Roasted coffee is fairly acidic, but it appears that almost all of 
the acid is water soluble and is extracted during brewing. Used 
grounds have essentially neutral pH, although the coffee beverage 
produced is rather acidic.

The measured pH of used coffee grounds was 6.9, with a significant 
amount of buffer capacity - adding the coffee to either acidic or 
basic solutions drove both towards neutral pH. The exact pH of used 
grounds will depend on the pH and alkalinity of the water used in 
brewing, but with any potable water, used grounds will be close to 
neutral pH."
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