How does soil pH affect tree health?

Christopher Wray
December 21, 2022

In Tri-Cities Washington, as well as many other regions, plants and trees are greatly affected by the PH of the soil and water they are grown in.

What is pH?

You may be wondering, what is pH? 

pH, according to Wikipedia is “a scale used to specify the acidity or basicity of an aqueous solution.” In other words, pH is a measure of how acidic or basic a solution is. Most commonly, soil and water pH are commonly measured to determine how well plants will do in a specific environment.


In horticulture, we commonly measure water pH or soil pH while we are growing plants, but once plants leave the nursery, not much is done to train homeowners and gardeners about the importance of pH. 

Today, I am hoping to help you understand the importance of keeping a healthy soil pH to help ensure your plants are sure to thrive in your landscapes.

Soil pH in the Tri-Cities Washington

In the Tri-Cities Washington area, pH varies by location, but in most areas, the soil is more basic. Basic means that the soil pH is above 8 on a scale of less than 6 being acidic, and greater than 8 being basic. So 7 is considered neutral, less than 7 is headed to acidic and over 7 is headed towards alkalinity.

Any area that gets irrigation directly from a river does not have a pH problem unless there are plants that need very acidic growing conditions.

The problem with pH in the Tri-Cities Washington specifically, is that our irrigation water that comes from wells is very high in calcium content which is the cause of high alkalinity issues…high pH.

How does soil pH affect plant growth?

According to the Mississippi State University Extension, plants grow the best in a soil pH of 6.5-7.5 The reason is that at certain pH, more nutrients are more readily available to the plant to take up.

When a plant is growing in a more basic environment or higher pH, potassium and calcium are more available to the plant, while in a more basic environment, aluminum, iron, and manganese are more readily available. 

When a plant is in either a super acidic, or basic environment (<4.0 and >8.5) the soil can become toxic.

How do plants react to a high pH?

Certain varieties of plants will each react in different ways to a high or low pH. In the Tri-Cities, in areas where both the water and soil are of a high pH, trees can be greatly affected. 

Certain trees, like varieties of Maple, are impacted by a high pH more than others. During the summertime, Red Maples in a high pH environment will yellow, and leaves will shrink in size due to the few nutrients found for growth.

Some varieties of trees will not display fall colors in the autumn, and others will become stagnant in growth.

What should you do if your landscape has a high pH?

If your soil has a high pH, you can lower this by adding gypsum (calcium sulfate), ground sulfur, or compost. 

You also can help lower water pH by adding sulfuric acid to the irrigation system. At Garden Gate, this is what we do to ensure our plants grow in a healthy pH environment.

Acidic soils can be helped by adding finely ground limestone or wood ash.

In my opinion, if your landscape will have a high or low pH, then choosing varieties of plants more adaptable to the pH is probably the easiest way to go although landscapes with toxic levels of pH will need treatment.(<4, >9)

In our area, it would be wise to stay away from red maples if your landscape is overly high in pH. You can choose trees like red Oaks or other large shade trees in their place.



Mississippi State University Extension:

Farmers Almanac:

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