Lowering pH

Alex McGregor waldenfarm at sprintmail.com
Fri Oct 20 11:20:13 EDT 2000


I would suggest you wait for your "complete soil analysis" before adding
anything.  A complete soil analysis should include major nutrients and trace
minerals, not just NPK and pH.

Adjusting pH is much more complicated than adding lime (calcium carbonate plus
acid yields carbon dioxide plus a calcium salt) or sulfur (formation of sulfuric
acid).  An out of range pH only shows us that something is wrong- that the mineral
balance in the soil for peak plant nutrition is out of whack.  Much like a fever
is an indicator of illness in a mammal- nothing more.

There are many anions (not just sulfur) that will lower pH.  The trick is knowing
which ones are in short supply to know which should be added.  And overloading the
soil with one mineral will cause the blocking of the plants' ability to absorb
others.  An example would be too much calcium blocking iron uptake.

By my own experience, my soil pH started at 6.4 (acidic) but a comprehensive soil
test also showed that the sulfur level was low.  Simplistic pH adjustment says I
should not add sulfur to an acidic soil.  I needed to add about 6 or 8 minerals
and did so with some of them in the form of sulfates to boost the sulfur level,
along with Ca, Mg, Boron, Mn, K...

I suggest you get a comprehensive test done by a soil testing service that
includes recommendations using Albrecht's system of balancing soil minerals for
proper plant nutrition.  You can find a list of these at:


I use Timberleaf (under "Emphasis on Mineral Analysis and Fertilizer
Recommendations").  They give you a comprehensive soil test that includes
recommendations for minerals by the acre for farmers or 100 sq. ft. for
gardeners.  They also do free consulting for 1 year with every test- by phone fax
and email.

For now, I would increase the organic matter in the beds and bioaactivity in the
soil by addition of compost to the surface as a mulch.  This will help make what
minerals are in short supply more available to the plants.  (The soil life does
this.)  I would wait for the results of a comprehensive soil test and
recommendations before adding any minerals- it's easier to add them than to remove
them from the soil.  Also, adding an acidic substance to change the chemistry of
the soil rapidly will kill off parts of the soil ecosystem leading to all kinds of
problems- depressing the natural nitrogen cycles, eliminating the life forms that
actively suppress plant pathogens, killing off plant symbiants that make nutrients
into a plant available form, reducing the number of microorganisms that produce
plant growth hormones...

Alex McGregor
Walden Farm

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