Many plant species do not thrive in the Miami Valley because they require better drainage and acid soil conditions. Throughout western Ohio, and many other parts of the Midwest, soils are neutral to slightly alkaline. When this condition exists, certain plant nutrients cannot be absorbed by plant roots. Elemental sulfur can be applied as a soil amendment to lower the pH or acidify such soils. This then allows these plants to absorb elements such as iron which is responsible for dark green leaves.

It is important to understand that this pH thing is real chemistry. It relates directly to the soil in your yard and the resulting experience you will have growing some pH sensitive plants such as azaleas, blueberries, some maple trees and blue hydrangea flowers.

pH = the measure of hydrogen molecules in a solution (in our case; the soil)

The soils in Western Ohio have high levels of free calcium carbonate (lime) in them which counteracts the hydrogen ions and results in higher alkaline soils. In addition, our soils are clay based (vs. sand) which makes changing the pH more difficult. When we add compost to our soils, thereby improving the texture, it becomes easier to adjust the pH.

The question arises: is it worth all the trouble to try to grow plants here that really would rather grow somewhere else where the soil conditions suit them naturally? For some people the answer is yes. Take blueberries for instance. Blueberry plants are long-lived (30 to 50 years or perhaps even longer), so considerable time and effort in preparing the planting site is a wise investment. Soils not within the range of pH acceptability for blueberry plant growth must be prepared BEFORE planting. When the pH is too high, the growth of the plant is slowed and the foliage turns yellow. If the pH is too high for an extended period of time, the plants will die. When several plants are to be grown together, more satisfactory results will be obtained if an entire bed is prepared rather than digging holes for individual plants.

To lower the pH when the pH of the soil is between 5.5 and 7.0 (most of our soils are near 7.0), add an acid peat, like compressed Canadian peat moss. Mix six inches of acid peat into the top six to eight inches of soil by rototilling. In addition to acidifying the soil, the peat increases the soil organic matter content. In an area 10’ by 10’ by 6 inches deep, start by using five pounds of elemental sulfur to reduce the pH. Elemental sulfur takes at least one year to adjust the pH. Iron sulfate reacts much faster than elemental sulfur (less than one month); however, the cost is greater. If you decide to use iron sulfate to lower the pH, start by making two applications of 10 pounds each, three months apart, to the 10’ X 10’ area. (Aluminum sulfate is not recommended, although it can acidify soil, because high rates of this compound can be toxic to roots.)

Test kits are available at many garden centers that allow you to easily test your soil’s pH and nutrient content. There are also laboratories which, when provided with a sample from your garden, will give you a more accurate analysis of your soil. Ask one of our associates for more information when you are in the greenhouse.

This information just scratches the surface of amending your soil. More reading will help you understand this critically important subject for plants you would like to have in your landscape and gardens that have difficulty growing in our native soils.

MVG - Growing Sustainably Since 1984