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Native Plant Synoptic Garden
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temperature than the air can easily become stressed or die during colder weather due to the wind
chill factor. Also the removal of moisture during freezing temperatures due to the wind can
ultimately cause desiccation (Harris et la., 2004). Like temperature and light, it is imperative that
the landscape planner collect and utilize precipitation and wind data for the area they are working
with.
Soil properties affect plant selection and growth; this would include properties affecting
water movement both in and on the soil, and water and nutrient holding capacities. Soil texture is
determined by the proportions of the particle sizes within the soil, and can affect water and air
movement as well as water and nutrient-holding capacity (Harris et la., 2004). The main
constituents in soil textures are sand, silt, and clay; these exist within a soil at different percents,
and those percents determine the overall soil texture. For example, if the soil has relatively equal
amounts of sand, silt, or clay then the texture is referred to as a loam (Craul, 1999; Harris et la.,
2004). Soil pH is another important factor to plant growth and health; soil pH greatly influences
the availability of nutrients. Soil reaction, referring to pH, is influenced by the types of
vegetation, rainfall, and the texture of soil; texture also affects soil drainage (Harris et la., 2004).
If a soil is well drained, many plants can be successful in soils with a wide range of pH. “By
considering the native habitat of a particular plant, an approximatio n of that particular plant’s
tolerance for pH ranges can be estimated” (Harris et la., 2004).
“The cation exchange capacity (CEC) is the ability of the soil to hold and exchange
positively charged forms of plant nutrients” (Young, 1990). Hydrogen (H + ), aluminum (Al 3+ ),
calcium (Ca 2+ ), magnesium (Mg 2+ ), potassium (K + ), ammonium (NH4 + ), and sodium (Na + ), are
the major cations in most forest soils (Brady et la., 2004). The cation exchange capacity (CEC) is
dependent on the amounts of organic matter and cla y in the soil, as well as the pH level (Young,
1990). CEC is normally higher in finer-textured soils, especially those containing colloidal clay
or humus (Young et la., 1990). CEC also shares a relationship with the pH level; when the pH is
really low (acidic), the CEC is low, and when the pH is really high (alkaline), the CEC is also
low; but when the pH is more neutral, the CEC is at optimal levels for most plant species
(Marschner, 1995). Specifically, cation exchange capacity and pH together help predict what
nutrients will be available for plant growth.
Two other characteristics that can be measured in a soil analysis is the amount of lead in
the soil and soil bulk density. Measuring lead levels is important because if soil lead levels are
too high they can become a health risk, especially to people. “On average, soils have 15 to 40
parts lead per million parts of soil” (UMass., 2004). Bulk density measures the weight of a soil
sample with a known volume (Harris et la., 2004). Bulk density, which is influenced by soil
texture, can determine the extent of or potential for compaction, water permeability and holding