Determining whether soil is acid or alkaline is important in gardening.
The pH scale goes from 0 to 14 with 7 being neutral. Each whole number drop on the pH scale indicates 10 times more acidity. For example, a soil with a pH of 5 is ten times more acid than a soil having a pH of 6. Numbers higher than 7 indicate alkaline soils – the higher the number the more alkaline the soil. Some people refer to acid soil as sour and alkaline soil as sweet.
Soil pH is very important for plants. It influences availability of fertilizer and toxic elements. It affects how well beneficial bacteria breakdown plant residues in your soil. It also effects nutrient leaching.
Most plants have a range of tolerance to the pH level of the soil. But plant nutrients are most available in the pH range of 5.5 to 6.5, which is the range most popular Florida landscape ornamentals prefer. However, certain plants need either acid or alkaline soils. For example, azaleas, blueberries, camellias, centipedegrass, bahiagrass, dogwoods, gardenias, hollies and magnolias need very acid soils – soils having a pH below 5.5. In areas where soils are alkaline, these plants grow poorly and may have yellow leaves. This is because certain elements begin to lock up in an insoluble form when the pH is too high or alkaline. Iron, copper and zinc are among these. Applying too much lime can cause this because lime makes soil more alkaline. Acid loving plants rarely need lime.
The only sure way to know if lime is needed is to have your soil pH tested.
A few plants that prefer a pH above 6 include ash, butterfly bush, elm, pink hydrangea, sycamore and yucca.
A reliable pH test will provide you with a numerical reading. If the pH is not at the optimum level, it can be raised by applying the correct amount of lime or lowered by applying the correct amount of sulfur. The exception to this is when the soil pH is excessively alkaline. This may be due to the over application of lime or it may be from some other source such as marl soil, an area where there are lots of sea shells in the soil or along the foundation of a building where there is concrete and mortar in the soil. In these situations, where you find that the pH is very high, your best bet is to select plants that are tolerant of high pH conditions.
Check with the UF/IFAS Extension Office in your County for details on having your soil pH tested.
Larry Williams, UF/IFAS Extension Agent, Okaloosa County, March 21, 2014
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