Sand for potting mixes

Tim Eck
Sat, 15 Nov 2014 17:37:13 PST
As far as I know, the only sand sold is silica sand (although they do sell a gravel grade for sand mounds that is typically limestone which has the same empirical formula as aragonite).  None of this is dangerous silicosis-wise in itself as it is far too coarse.  If it is used for sandblasting, it creates new dust which is dangerous.  And if you expect to be mixing it dry, you should probably wash the sand or buy a washed sand that has the dust removed as in play-box sand.  Concrete sand has varying size particles which has less bulk porosity than a single-sized sand.  As the size of the sand grains diminishes, the porosity will shift from air porosity to water porosity.
Silica is slightly acid while aragonite is somewhat alkaline. 

-----Original Message-----
From: pbs [] On Behalf Of
Sent: Saturday, November 15, 2014 5:20 PM
To: Pacific Bulb Society
Subject: Re: [pbs] Sand for potting mixes

So, I suspect that calcium carbonate sand might change the pH, and that is why it is undesirable for potting mixes?


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From: penstemon
Sent: ‎Saturday‎, ‎November‎ ‎15‎, ‎2014 ‎5‎:‎07‎ ‎PM
To: Pacific Bulb Society

>I have heard for years that one needs to use “silica sand” for bulb 
>potting mixes. I wonder how “silica sand” differs from other sand. I 
>try to find very coarse sand because it is not as likely to compact. 
>The best stuff I found was from a stream bed. But was it “silica sand?” 
>Isn’t sand generally a silicate mineral anyway?

I would have said yes, but a quick check of the apparently-omniscient Wikipedia says that silica sand is the most common form of sand, followed by sand from calcium carbonate (aragonite).
The sand I use is the stuff called "paving sand"; comes in bags. The grains aren't uniform in size.


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