What is pH?

The small “p” stands for potential, and the capital “H” stands for Hydrogen. It pertains to a soil’s acidity or alkalinity. In some gardening books you may see soil described as being sweet or sour. Sweet soil means a soil is alkaline whereas a sour soil means it is acidic.

Why is pH important to plant health?

A soils pH is of paramount importance. It affects soils fertility by controlling how well nutrients are dissolved. You can fertilize all you want but if your soils pH is out of range your plants will be unable to access or utilize that fertilizer. Also, while plant nutrients are being rendered insoluble, toxic elements become more soluble and can potentially kill plants or severely damage roots. In addition, beneficial soil bacteria will not grow in either highly acidic or highly alkaline soil and without the help of these guys your soil’s structure will be poor.

Symptoms of excessively high or low pH include plants exhibiting yellowing leaves, lack of proper growth and flowering and in severe cases death of the plant. Certain plants thrive in an acid soil while others prefer a more alkaline environment. Knowing what your soils pH level is will help you to choose suitable plants for your soil. It will also help you to correct any imbalances before they become a real problem.

A soils pH can also affect flower colour. Hydrangeas are a prime example. When a soils pH is more to the acidic side blooms will be blue. When the soil is more to the alkaline side blooms will be pink. This occurs because the soil pH affects the availability of aluminum in the soil.

Determining your soils pH

For the typical small-scale home gardener, a simple do-it-yourself kit will usually suffice. Available from Vigoro and CIL many garden centers now carry them. Collect a soil sample (as described earlier). Follow the instructions provided with your kit. Alternately you can use litmus paper. Dip the tip of your litmus paper into a bit of garden soil that has been mixed with distilled water. As the paper changes colour compare it to the colour chart provided. There are also pH meters available for purchase. They are simple, portable and use electrodes to measure the hydrogen ion activity. Other simple home tests include using vinegar or baking soda to test soil pH. Alkaline soil will fizz when vinegar is added, and acidic soil will fizz when baking soda is added. As with all other forms of soil testing you can have your soil professionally tested at a laboratory. This is recommended especially for commercial or larger scale gardens.

Altering your soils pH

A pH level of 7 is considered neutral but as already mentioned most plants perform best at a pH level between 6.3 and 6.8. To raise the pH level of and acid soil add calcium carbonate, ground dolomite limestone or wood ashes and switch to fertilizers and amendments that do not acidify the soil. To lower a soil pH add agricultural sulfur or pine needles. Add organic matter and switch to acidifying soil amendments and fertilizers. It would also be wise to test for salt problem and treat any you may incur. Note: Add your pH amendments to the soil about 1 month prior to fertilizing and well in advance of planting. Retest after 1 month. If the pH is still too high or low give the soil a second treatment (never apply more than the manufacturers recommended amount at one time). It can take years to drastically alter the pH level of a soil. You will need to regularly test and amend your soil, if its natural pH is quite different from the one you are attempting to create.

Photo Credit: photo taken by the author.

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