High altitude soils tend to be alkaline due to the lack of rain
to wash salts out of the soil. An alkaline soil has a pH higher then
7.0 (see the links below for more
information on the pH scale). Most vegetables and flowers prefer
a slightly acidic to neutral (6.5 to 7.0 pH) soil. When the soil
is too alkaline (or acidic), plants cannot use the nutrients in the soil
and do not grow well. Simply adding fertilizer to the soil does not
help; you must correct the pH of the soil for fertilizers to work
Lewis Hill (see below for
examples) wrote an excellent reference of the pH requirements for most
vegetables. I have not found a reference on the internet that gives
the pH requirements for plants. If you know of one, please contact me and let me know!
My vegetable garden soil initially tested at 8.3 pH which is too high
for plants to successfully take up the nutrients in the soil. I do
the following to lower the pH of my soil:
1. Add organic matter. While
this will not dramatically lower the pH of any soil, organic matter does
help the plants take up nutrients as well as helping the soil retain moisture.
I mostly add aged horse manure which I can get free in abundance here in
rural Pine. The usual sources of organic matter such as compost or
peat moss work well also.
Every few years, we have a major thunder storm which washes pine needles,
cones, twigs, and other organic matter (as well as rocks) down into one
of our meadows. Rather then let this organic matter stand as large,
unsightly piles throughout the meadow, we rake and pick up the material,
pile it into our old pickup truck, and place it into my vegetable garden.
Pine needles are naturally acidic and the material, worked into the soil
with my tiller, quickly decomposes. A gardening windfall from a seemingly
2. Never add wood ashes. I
added the ashes from our wood stove to the garden soil for the first few
years that I gardened. Wood ashes are a good source of potash and
I did not want to waste the ashes. However, over the years I noticed
that the garden soil was ever more alkaline and I had to add more and more
sulphur to attain a pH where vegetables would grow. Wood ashes are
very alkaline. Now, we scatter the wood ashes around in the forest
(making sure there are no hot coals in the ashes) and never place the ashes
in the garden. The forest plants seem to benefit from the potash
and, since the wood ashes are spread over a wider area, the soil does not
seem to be adversely affected.
3. Add sulphur or ammonium sulfate.
The best method for lowering soil pH that I have found is to add sulphur
directly to the soil prior to planting the garden. 4 lb. sulphur
per 100 square feet will lower the pH one point. Ammonium sulfate
is also effective but is 23% sulphur and takes four time as much to lower
the pH one point. However, ammonium sulfate also contains 21% nitrogen
which is an added benefit. I have also used Miracle Grow Acid Fertilizer
during the growing season whenever I notice any plants turing yellowish.
I apply the Miracle Grow directly to the leaves using a hose sprayer attachment.
The only source that I know for garden sulphur is The Rocky Mountain
Seed Company (P.O. Box 5204, Denver, CO 80217-5204, telephone 303.623.6223,
no web address). Do you know of any other sources? I use the
granular soil sulphur which is easy to measure and apply. It costs
$12.50 per 50 lb. bag.
Since the soil pH is so important to maintain properly, I invested in
a Hanna Instruments Checker 1 pH meter. I have used soil test kits
but I found the meter to be easier to use, more accurate, and, since I
test each garden bed separately, cheaper in the long run as there are no
chemicals to use. I listed some
sources for pH testers below.
to pH Information Sites:
Water Properties. A basic tutorial on pH mainly relating to water properties
but is informative about pH also. Directed to science students.
Requirements for Some Vegetables. Information taken from "Cold
Climate Gardening", Lewis Hill, Page 32 ISBN 0882664417
Soil pH Wikipedia - the webpage has an excellent table on the effect of nutrient availability in relation to soil pH.
Changing the pH of Your Soil Prepared by Marjan Kluepfel, HGIC Information Specialist, and Bob Lippert, Extension Soil Fertility Specialist, Clemson University. Towards the bottom, there is a good section on lowering soil pH.
The pH Factor
Created by the Miami Museum of Science, this is a very basic, low level
but informative site directed to those teaching science.
|Alkaline (above 7.0
|Near Neutral (6.5 to
|Acid (5.5 to 6.0 pH)
to Sources for pH Testers (I do not endorse any of these sites but
list them for your information only):
Use their search engine with "ph and tester" and you will get a list of
their instruments. I use the Checker 1 (MI 98103) but they list other
pH meters that also look interesting.
Search on "pH" and you will get a list of their pH meters.
While you can find soil test kits through many catelogs/sites, I added
Johnny's because of their reliability and the fact that they test all the
products they sell.