Today’s article on soil pH will conclude the Understanding Soil Nutrients Series. These articles on soil nutrients will cover a brief summary of each main soil nutrient. If you missed the previous entries to this series, here they are:
Although pH is not a soil nutrient, I felt it was very important to bring it up during the soil nutrient discussions. pH levels can have a very important role in the availability of nutrients to plants.
What Is pH?
pH is a measure that determines whether the soil is alkaline or acidic. Fortunately, a smart scientist developed the pH scale back in the day. The pH scale runs from 0 to 14, with neutral being in the middle at 7. Less than 7 is considered to be acidic, while more than 7 is alkaline. The ideal pH level is typically neutral – somewhere near 7 on the pH scale. Neutral soils are also called “sweet”, while acidic soils are “sour”, and alkaline soils are “bitter”.
Different vegetables and fruits may require difference pH levels. For instance, blueberries grow better in acidic soils, and cabbage fairs better in alkaline soils. Generally, most vegetables and fruits prefer a neutral or sweet soil. A good rule of thumb for most gardens is a pH level around 6.5.
Soil pH and Soil Nutrients
Soil pH is very important because soil acidity or alkalinity directly affects plant growth. If a soil is too sour or too sweet, plants cannot take up nutrients like nitrogen (N), phosphorus (P) and potassium (K). Plants need these nutrients to thrive and fight off disease and stress. If the soil pH levels are too far out of the optimum range, the plant roots may not be able to absorb and uptake nitrogen and other nutrients. The nutrients are said to be “locked up”. The soil pH level is also important for bacterial growth that helps with decomposition of organic materials in the soil.
If your vegetables appear to suffer from nitrogen deficiency, pH could be the culprit. This is why a complete and thorough soil test is important to the health of your garden. Home soil test kits and the tests administered by local cooperative extensions provide data on pH levels in your soil.
Adjusting pH Levels In Your Soil
If your soil is too acidic, you need to add alkaline material. The most common material is ground limestone. Ground limestone breaks down slowly, but it does not burn plants like “quick lime” does. Apply it to the garden and lawn in the fall to allow time for it to act on soil pH before the next growing season. A rule of thumb for slightly acid soils: apply 5 pounds of lime per 100 square feet to raise the pH by one point.
If your soil is too alkaline, you need to add a source of acid. Options include pine needles, shredded leaves, sulfur, sawdust and peat moss. Pine needles are a good source of acid and mulch. Peat moss with a pH of 3.0 is often recommended as a soil additive. Before you use it though, consider the other options, because peat moss is nutrient-poor, expensive, and it’s a nonrenewable resource.
Using well-aged manures and compost can change acidic or alkaline soils to a neutral pH level over time. Compost is one of the easiest and best ways to adjust pH levels. Remember, using chemical fertilizers tend to create an acidic pH level in soils.
Adjusting the pH in your garden soil does not happen over night. It takes some time, usually spread out over a couple years, to get your soil pH levels to optimum levels. It is best to work on the soil pH in the fall or early spring. If you wait until planting time, it is probably too late.