Why Does Soil Ph Matter?
 | Author:
Allison Kosto, MSU Broadwater County Extension Agent
MSU Broadwater County Extension Agent |
Allison Kosto
MSU Broadwater County Extension Agent
Soil should not be confused with dirt. Dirt is unclean; it gets underneath your fingernails. Soil, on the other hand, is a dynamic material that has living parts. Soil is comprised of minerals, water, gases, organic matter and microorganisms. All of these components give soil its unique characteristics. Soil is not the same in Montana as it is in Florida. In fact, it may not be the same on one side of your yard as it is on the other.
The environment along with soil composition attributes to the soil pH. I’m sure you are somewhat familiar with pH. The pH scale ranges from 0 to 14 with 7 being neutral. Numbers less than 7 are acidic and numbers greater than 7 are alkaline or basic. Lemon juice is acidic, and bleach is alkaline.
Soil pH has an ability to affect plant growth by influencing nutrient availability. Plants thrive best in different pH ranges. For example, blueberries prefer acidic soils. Generally, most plants grow well when the soil pH is 6 to 7 (slightly acid to neutral).
Due to Montana’s arid environment, we tend to have soils with a high pH, usually ranging from 6.5 to 8.5. The average for Broadwater County, based on samples received by my office over the past three years, is about 7.8. The best way to find your soil pH is to use a reputable lab. Home testing kits are available for pH and other nutrients. However, their accuracy is questionable. A list of labs is available from the Extension Office, and we can even send the sample for you. A basic garden soil analysis is about $17 plus shipping.
As I already mentioned, pH affects nutrient availability. But why does this really mean?! Soil pH affects how the soil attracts and releases nutrients. In high-pH soils, iron, manganese and boron are not very accessible to plants. Most commonly in Montana, there are issues with iron uptake. Some plants, including many trees, are more susceptible to iron deficiencies, which cause the leaves to turn yellow while the veins stay bright green, called interveinal chlorosis. On the other hand, in acidic soils, magnesium, calcium and phosphorus tend to be limiting.
If you have a high pH soil, one of the first questions you’ll likely ask is “How do I change it?” Unfortunately, it’s not easy. The two most common soil amendments to lower pH are sulfur and aluminum sulfate. Aluminum sulfate works more quickly, whereas sulfur can take several months. Routinely adding organic matter can also improve the pH. Always be cautious when adding fertilizer and soil amendments. Too much of a good thing isn’t always a good thing. Use your soil test to determine how much fertilizer or organic matter is needed.
Acidic soils and the need to raise pH are rare in Montana. Cropland in central Montana is starting to have an issue with soil acidification due to high fertilizer inputs for many years. Limestone is the common amendment used to raise pH. While this issue is increasing across the state with cropland, it is not an issue commonly seen in gardens.
Even with amendments, it is extremely difficult to cause a major change in your pH. However, by knowing and understanding your pH, you can make better management decisions. For example, blueberries thrive in acid soils. If you have a pH of 8.0, then you may have to come to terms with the fact that blueberries simply won’t produce well. You also may need to annually fertilize your trees with iron.
If you have any questions about soil testing, fertilizers or soil amendments, stop by your local MSU Extension Office at 416 Broadway or contact us at 406-266-9242 or allison.kosto@montana.edu.
