University of Florida

The Neighborhood Gardener: Soil pH

(Continued from the previous page)

Changing Soil pH

For best plant growth and performance, always choose landscape plants suited for the natural pH of your soil. While there are additives that can raise or lower the pH of soils, the effects of these materials are often short-lived. However, if you are determined to change your soil's natural pH to grow a specific plant, you have the two following options.

1. Raising the pH of Acidic Soils
To raise the pH of acidic soils, add a liming material like calcium carbonate or dolomite. Dolomite has the added benefit of supplying magnesium, which is often deficient in Florida soils. Have your soil tested before applying any liming materials to the soil, because many natural and urban soils in Florida have an alkaline pH. If a soil test indicates that your soil is too acidic, have a lime requirement test performed. The lime requirement test will measure your soil's natural ability to resist changes in pH. This test is offered as part of the standard landscape and garden soil test offered through the soil testing lab. Results of this test will indicate exactly how much lime you need to apply to reach a target pH. You will then be able to apply the correct amount of agricultural limestone.

In order for lime to be effective, it should be thoroughly mixed into the soil. This is easily accomplished before planting a garden or landscape. When applying lime to established landscapes or turf, lime should be surface applied and watered in.

2. Lowering the pH of Alkaline Soils
Lowering the pH of strongly alkaline soils is much more difficult. In fact, there is no way to permanently lower the pH of soils formed from high-calcium materials such as marl, s hell or limestone, as well as soils severely impacted by alkaline construction materials. Under these circumstances, it is best to select plants which are tolerant of high-pH conditions to avoid continuing plant nutritional problems.

Soil pH can be temporarily lowered by adding elemental sulfur. Bacteria in the soil act to change elemental sulfur into sulfuric acid, effectively neutralizing soil alkalinity. However, the effects of elemental sulfur are localized to the area that was amended, and the effect is temporary. Soil pH will begin to rise shortly after soil bacteria exhaust the added sulfur supply. This effect will require repeated applications of sulfur to ensure the soil remains at the desired pH.

If too much sulfur is added, or if it is added too frequently, it can actually injure or kill your plants. Therefore, it is important to never apply sulfur in excess of 5 to 10 pounds of sulfur per 1,000 ft2 per application. If you decide to apply sulfur, make sure to monitor your plants.

Summary
  • Before establishing or renovating a landscape, submit a soil sample to the soil testing lab.
  • Consider the pH of your soil before selecting plant materials for your landscape.
  • Choose Florida-Friendly plants appropriate for your site, and correct soil pH only if it's substantially higher or lower than required by the plants you are growing.
  • To avoid damage to your plants, always have your soil tested before adding lime or sulfur to the soil.
  • Finally, if you are determined to grow plants that aren't suited for your soil, consider growing them in containers, where the soil will be easier to amend.

 

Reviewer: Amy Shober
Adapted from: Soil pH and the Home Landscape or Garden

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