Re: lowering soil pH

> Sulfur and aluminum sulfate can be added to the soil to lower the pH
> (more acid). Aluminum sulfate will change the soil pH instantly because
> the aluminum produces the acidity as soon as it dissolves in the soil. 
> Sulfur, however, requires some time for the conversion to sulfuric acid
> with the aid of soil bacteria.

Personally, I always use sulfur when I can, but if I need immediate
results I'll use aluminum sulfate.

Aluminum sulfate has a fair number of risks/problems, though.  One is 
that it hydrolyzes in water to form sulfuric acid, so if you haven't
mixed it in your soil well, watch out!  Granted, it's a dilute form, 
but it can still damage plants.

The other issue is aluminum toxicity -- many plants (except for
Hydrangea macrophylla) will suffer when aluminum sulfate is used.

A good middle ground is iron sulfate -- it can lower the pH within 
3-4 weeks.  However, if your soil is very alkaline you'll have to 
apply it in stages to keep your soluble salt levels down.

What's your target/current pH?  What's your soil like?  The drainage
could impact application rates.

Chris

http://www.bonvivantnursery.com/                     Bon Vivant Nursery
http://www.hort.net/gallery/      4023 online plant photos and growing!
http://www.hort.net/gallery/date/2006-07-26/       The latest additions

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