Soil pH 101 for Georgia Gardeners

Next in our series of posts on soil health, we want to explore soil pH and its importance to garden food crops.  This involves remembering some of your high school chemistry so grab your cup of coffee to get the brain waves working.

pH is the measure of hydrogen ion activity

Soil acidity is a chemical factor that can affect food crop growth.  Soil pH, the measure of hydrogen ion activity in a solution, is important for soil nutrient availability.

Think back to high school chemistry and that daunting Periodic Table.  The element hydrogen (H) is located in the upper right hand corner and is carries a +1.  That +1 means it can easily interact with elements with a -1 or a -2.  Remember water is H2O.  Two hydrogen +1s and one oxygen -2.  Sound familiar?

Soil pH basics for Georgia Gardeners
The daunting periodic table

The pH scale is graduated from 0 to 14. The midpoint (7) separates acid from alkaline. Any number below 7 is acidic—the lower the number, the more acidic.  The lower the number the increased H +1 activity.

A soil pH above 7 denotes alkaline soil conditions.   The higher the number the increased OH -1 activity.  The pH scale is logarithmic; a soil with a pH of 5.0 is 10 times more acidic that one with a pH of 6.0 and 100 times more than a pH of 7.0.

pH affects nutrient availability

This activity of H+1 and OH-1 can bind up nutrients that plants need by bonding with other soil ions.  This is a very simplistic explanation and true soil chemistry is much more complicated.  But, I think this gives you an idea of how pH is can be very important to plant growth.   For example, at a soil pH of 5.0 much of the nitrogen fertilizer you add to the soil won’t be available to be absorbed by your plants!

Soil pH basics for Georgia Gardeners
Nutrient availability and pH. The wider the band the greater the availability. (USDA)

Correcting soil pH

A soil pH that is too low or too high can decrease the amount of nutrients absorbed by plant roots. Lime can be used to increase the soil pH, while sulfur can be used to decrease it.  An accurate measure of soil pH is needed before corrections should be made.

Soil pH also influences other reactions in soil, such as microbial activity. Most food crops grow best in soils with a very slightly acidic pH, close to a neutral pH of 7.   Most soils in Georgia, however, are too acidic, and lime is often needed to maintain ideal growth conditions.

Winter is a great time to have your soil pH tested.  Contact your local UGA Extension office for assistance.   To find out how to properly collect your soil for testing see Soil Testing for Home Lawns, Gardens, and Wildlife Plots.

Happy Gardening and congratulations on making it through the chemistry lesson!

Healthy Georgia Soil 101

Soil From a Community Garden in Woodstock.
Soil From a Community Garden in Woodstock.

Healthy plants start with healthy soil.  Period. No exceptions. You will be more happy with yields and vegetable quality if you start with good soil.  You will deal with frustration and possibly more disease and pest problems if you ignore your soil.

Soil is NOT just dirt.  It is alive and complex.  It is a relationship of soil minerals, organic matter, organisms, water, air, and plants.  The mineral component is made up of a mixture of sand, silt, and clay.  Organic matter is important as it contributes to moisture and nutrient retention.  Soil is a habitat for fungi, bacteria, actinomycetes, algae, protozoa, nematode, and earthworms and small mammals.  All this is important to the health of your plants.

Sometimes cities and municipalities donate land for community gardens that may have been undesirable for other uses.  Do you know what the land was used for before your garden was started?  A site that was previously used for manufacturing could have lingering by-products in the soil that could be a problem.

Many times community gardeners use raised beds and import soil and compost.  Know where that soil or compost comes from.  One community garden got a large amount of horse manure donated.  That manure contained herbicide residue that affected the tomatoes the gardeners tried to grow.   Also, soil that has been sterilized is void of desirable microorganisms.  Consider adding a compost pile to your garden (see June 25th post – Composting in the Community Garden).

Soil Sample Bag
Soil Sample Bag

If you have not been happy with the quality of your plants, the first step is to get your soil tested.  You can get information on soil testing from your local UGA Extension Office.  Instructions can be found in the publication Soil Testing.  In general, take a few sub-samples of your soil at a six inch depth.  Mix these sub-samples for an overall sample.  When you submit this to your Extension office it goes to the University of Georgia soil testing laboratory and within a couple of weeks you will get a test result page with information on your soil fertility and pH.  You will also get recommendations on how to improve your soil based on what you are growing.  There is a small fee (approximately $6-8)  involved but it is the best investment you will make!  Also, depending on the size and layout of your garden, not everyone in your garden needs to soil test.

Just think of all the things at work in your soil.  You will never call it “dirt” again!

Happy Gardening!