Soil Type and Plant Health

Common Landscape Pitfalls that Affect Plant Health – Soils Edition

Landscapes with plants that match their preferred growing conditions require less water, fertilizer, pesticides, and maintenance than landscapes with plants growing in the wrong location. When choosing the right plant for the right place, there are a number of factors to consider to ensure a long-lived, healthy landscape. Characteristics of your soil, like pH and compaction, play a huge role in the well-being of your landscape plants.

Soil pH

Soil pH is a measure of the acidity or alkalinity of the soil. A pH value of 7 is neutral, a pH of less than 7 indicates acidic soil, and a pH greater than 7 is alkaline. Sometimes you may see a soil referred to as "sour" (meaning acidic) or "sweet" (to mean alkaline).

Soil pH directly affects the growth and quality of many landscape plants by influencing both the chemical elements in the soil and the soil microbial processes.

Landscape plants may exhibit nutrient deficiency or toxicity symptoms as a result of highly acidic or alkaline soil pH. For example, when soils are acidic the availability of plant nutrients like potassium (K), calcium (Ca), and magnesium (Mg) is reduced. At the same time, acidic soils have increased availability of potentially toxic elements like aluminum (Al), iron (Fe), and zinc (Zn).

In Florida soil pH varies widely; the median soil pH is 6.1 which is slightly acidic. However, soils formed around pine flatwoods can be quite acidic, while soils formed from limestone, marl, or seashells are more alkaline. Alkaline soils are common in coastal areas as well as home landscapes. In home landscapes the alkalinity is often the result of building materials, rich in calcium carbonate, that may have been left in the soil after construction.

The best way to deal with this variation is to know the pH of your soils and select the right plants for your soil conditions. You can determine soil pH by sending a soil sample to a reputable lab like the UF/IFAS Extension Soil Testing Laboratory.

Many common landscape plants are well-suited to a wide range of soil pH levels. However, there are some beloved acid-loving plants like azaleas, blueberries, and gardenias that don’t grow well in soils that have a pH of 5.5 or greater. Knowing the pH of the soil in your specific landscape will allow you to choose the pants best suited for your location. Remember, it’s important to put the right plant in the right place!

An ixora shrub that's very small, with yellow leaves and no flowersAn ixora shrub with bright green leaves and many orange-red flowers

Left photo: An ixora shrub in high-pH soil (wrong place).
Right photo: An ixora shrub in low-pH soil (right place). UF/IFAS.

Soil Compaction

Soil compaction is a consequence of urban development activities and can lead to problems with soil drainage, aeration, nutrient cycling, and plant growth. How individual soil particles are arranged forms the soil structure. Spaces between particles can be filled with water or air and interconnected spaces allow for movement of water through the soil. Soil compaction occurs when the soil structure is compressed. In urban areas, soil compaction is often caused by the use of heavy equipment during construction and constant traffic (by foot or equipment) in existing landscapes.

Soil compaction reduces the total number and size of pores between soil particles. These pores are critical for supplying plant roots with water and oxygen. Compaction also increases resistance to root penetration which makes it harder for roots to grow through the soil. Soil compaction can extend more than a foot below the surface with the most compacted depths being more than 6 inches below the surface. This can cause plants to develop shallow roots which can lead to poor growth.

dying tree in parking lot surrounded by cars

This tree probably looked fine when first planted in this parking lot, but compacted soil is taking its toll. UF/IFAS.

One way to determine if soil compaction is a problem in your landscape is to check for resistance to soil penetration. This can be done using a garden shovel, a soil probe, or even a sharpened wood pencil. If you have trouble inserting these implements into the soil to depths greater than a few inches, you may have a problem with compaction affecting the root zone of your plants.

Addressing soil compaction can be quite tricky. Tilling, plug aeration, air tilling, and the addition of compost to your soil can all be used to improve compacted soils. Deciding which method to use will depend on how compacted the soil you are working with is, as well as what your budget is like.

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