Simply Soil: Soil Basics

But for landscape contractors who want their clients to have more than a mental image of the perfect landscape, soil health cannot be overlooked.

Even though soil testing and improvements are not substitutes for premium varieties, fine weather and proper plant maintenance, they remain useful tools for sustaining quality turf and plant material.

Contractors first must care for the soil that feeds the landscape if they are going to properly maintain, fertilize and grow lush plants. Discovering - rather than guessing - the soil’s ingredients is the first step.

LIKE A SPONGE. Soil is defined as "a complex medium of organic and inorganic materials providing water and nutrients for plant growth and development," according to John Street, extension agronomist, Ohio Cooperative Extension Service, The Ohio State University, Columbus, Ohio,

In most lawns, the basic inorganic soil elements are silt, clay and sand, pointed out Richard Pete, president, Planet Green, Charlotte, Vt.

"The percentages, by weight, of each of these three components are used to determine the texture of the soil," Street said, explaining that organic matter is the remains of the previous plant growth in the soil and generally ranges from 2 to 4 percent in most Ohio lawns. "Soil nutrients needed by turfgrass and other plants are retained on the surfaces of soil particles and organic matter called exchange sites. The total number of nutrient exchange sites is referred to as the Cation Exchange Capacity (CEC) of the soil. The higher the CEC value, the richer the soil is in the contents of nutrients." (see Soil Test Interpretation below).

Soil microbes digest organic matter, creating humus, which is a characteristic of perfect loam soil. Humus, according to Pete, is a basic soil element that can only be manufactured by healthy soil. It is also the element most neglected by contractors.

Landscape contractors who know nothing about soil are like doctors who know nothing about nutrition, Pete remarked. "What’s happening above ground isn’t always more important than what’s happening below ground," he said. "Without healthy soil, healthy plants aren’t possible."

But before contractors rush to achieve healthy, loam soil on their clients’ properties, they should examine its appearance and texture. One way for contractors to see and feel healthy soil is to go into a forest and pull back the top soil layer to reveal the microbial layer, Pete said. "This soil is top quality, containing about 20 percent organic matter," he noted. "This is where the soil microbes are feeding on organic matter."

Perfect soil should be sponge-like with a balance between spaces that stick together and porous areas. Soil that is more like a brick, completely stuck together, or like sand, falling apart, is very unhealthy, Pete pointed out. "Sponge-like soil holds more water than most things, but also allows water to pass through it," he said.

TAKE THE TEST. Nutrient-deficient soil is normally evident by plant or lawn appearance, Street said. "In turfgrass, symptoms include a light green color, weak or thin turfgrass density despite generous applications of fertilizer or a rapid decline in quality during periods of stress," he said.

The best way for contractors to determine if a client’s property lacks important nutrients and what they should do is by collecting a soil sample and having it tested at a laboratory, a list of which can be obtained through most university extension services.

"To apply optimum levels of nutrients or lime to your soil, you need to know the existing pH and the availability of essential plant nutrients," explained Zane Helsel, director, Rutgers Cooperative Extension, Cook College, New Brunswick, N.J.

The typical soil test determines the soil pH, salinity, nitrates and levels of primary nutrients (phosphorus, potassium, calcium, magnesium, sodium and sulfur) available to plants and turf. The routine test can also provide the basic N-P-K (nitrogen - phosphorus - potassium) fertilizer recommendations. "The soil test takes the guesswork out of fertilization and is extremely cost effective," Street said. "It not only eliminates the waste of money spent on unnecessary fertilizers, but also eliminates over-usage of fertilizers, hence protecting the environment."

Soil test prices vary slightly from region to region. For instance, a standard soil test is $8 at Rutgers Soil Testing Laboratory, Milltown, N.J., while a quick pH test is $3 and other more specific tests range in price from $3 to $40. A routine test at the Virginia Tech Soil Testing Lab, Blacksburg, Va., is $7 for in-state samples and $10.50 for out-of-state samples. And a routine analysis at the Soil, Water and Forage Testing Laboratory at Texas A&M University - Soil and Crop Sciences, College Station, Texas, is $10. Some tests include fertilizer and lime recommendations, others do not.

When contractors are searching for a soil testing lab to work with, Lynn Griffith, president, A&L Southern Laboratories, suggested finding one they are comfortable with and will continue using. "Don’t use different laboratories or you can become confused by the differences in methods and units," Griffith said, pointing out that some important factors in choosing a laboratory are quality of data, price, soil testing method and ease of understanding the report.

The proper soil test depends on landscape type and condition. Most contractors request a routine test, but lime tests and organic matter tests also are important. Micronutrient, boron and detailed salinity tests are typically used for specialty crops or environmental or research purposes, remarked Tony Provin, assistant professor and soil chemist/laboratory director, Soil, Water and Forage Testing Laboratory.

Soil samples can be taken any time of year, but sampling when the soil is extremely wet is not recommended. Fall months are best, according to most extension agents. "Soil samples can be taken in the spring or fall for established sites," Street attested, adding that sampling every two to three years is usually adequate. "For new sites, soil samples can be taken anytime when the soil is workable. Most people conduct their soil tests in the spring. However, fall is the preferred time if one wants to avoid the spring rush and suspects a soil pH problem. Fall soil testing will allow you ample time to apply lime to raise the soil pH. Sulfur should be applied in the spring if the soil pH needs to be lowered."

Soil testing also is suggested before lawn or landscape establishment, said Bruce Spangenberg, extension educator, horticulture, Rockford Extension Center, Rockford, Ill. "Lawns will get off to a better start if soils are modified at this time," he said.

Steve White, owner, Second Nature Lawn Care, Nashville, Tenn., agreed. "First, you have to get the soil ready," he said. "Skip this step and you’ll have pitiful petunias and awful alyssum."

Soil test results and fertilizer recommendations usually are mailed in two weeks, depending on the laboratory. "Make sure you fill out the form for the types of plants you grow or will be growing," Street stressed. "Otherwise, no recommendations will be given."