Plant Health Starts With the Soil

By Jane Morse, University of Florida/IFAS Extension Agent, Pinellas County

Did you know there are more than 70,000 different kinds of soil in the United States?

With all these different kinds of soil you can imagine the variations of their soil properties. How much water or nutrients they hold, their pH and drainage can all be wildly different. Unfortunately for most Florida gardeners our soils are mainly sand. Sand does not hold on to much of anything, so water, nutrients and pollutants flow right through and into our ground water.

Soils are also characterized by their alkalinity (high pH) or acidity (low pH). Most plants prefer soils in the 5.5 to 6.5 pH range, which is slightly acidic. This is also the pH range where most plant nutrients are easily available to plants. When soil pH is either above or below this optimum range plants may start to show nutritional deficiencies or toxicity symptoms.

Our Florida coastal soils tend to be very alkaline, whereas soils that formed under pine flatwoods can be very acidic. Sea shells, marl and limestone are very high in calcium and are the main reason for our coastal soils being so alkaline. Some calcium-rich building materials such as concrete and stucco can also raise the soil pH. Plants grown in alkaline soils are commonly lacking these plant nutrients: iron, manganese, zinc and boron.

To determine your soil pH you can send a sample to a trustworthy lab such as the University of Florida Extension Soil Testing Laboratory ( Once you know the pH of your soil you can choose the plants best suited to your soil, or understand why some plants are not growing well. Strongly alkaline soils are generally a greater problem in landscapes and proper plant selection is very important. Acid-loving plants such as azalea, ixora, gardenia and blueberry will never do well in an alkaline soil. There is no way to permanently lower the pH of soils formed from high calcium materials, so proper plant selection is critical for plant health.

The University of Florida Extension Soil Testing Laboratory (ESTL) can also provide a fertility analysis. This test tells you how much phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) are in your soil. This report also includes pH, lime and fertilizer recommendations for selected lawn and landscape plants based on your soil sample.

To avoid damage to your landscape plants, always have your soil tested for pH and/or lime requirement before adding lime or sulfur to the soil. If you want to grow plants that are not suited to your soil pH, consider growing them in pots with another soil that has been amended to provide the proper pH.


Posted: September 11, 2009

Category: Home Landscapes

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