A successful and productive garden begins with healthy soil

Gardeners often disregard the impact soil has on the health and longevity of their plants, but soil preparation is key to planting a successful garden.

Experts say gardeners should focus on maintaining and enhancing ecological balance in the garden by increasing biodiversity and crop rotations, improving soil and enhancing water conservation, typically with the exclusion of synthetic fertilizers and pesticides.

According to South Dakota State University (SDSU) Extension, soil health is defined as the ability of soil to function in an ecosystem which can sustain plants, animals and humans.

Healthy soil has a good physical structure, with enough pore space to contain oxygen to fuel the growth of plant roots and soil microbes. 

Soils with good structure allow water to infiltrate easily without pooling or running off and also hold enough water to support good growth of plants and soil microbes.

Healthy soil requires robust microbial activity and diverse microbial populations. 

In an acre of healthy soil, the upper six inches will contain up to 23,000 pounds of microbes.

Organic matter

“Soil is not lifeless and inert, it is alive,” states SDSU Assistant Professor and Extension Horticulture Specialist Kristine Lang in an SDSU Extension article published in May 2021.

She mentions a single teaspoon of healthy soil can house up to a billion bacteria, several yards of fungal filaments, several thousand protozoa, 40 to 50 nematodes and a variety of smaller insects and arthropods which work harmoniously throughout a complex soil food web responsible for life on this planet.

Many gardening publications – whether they promote organic methods or not – tend to agree on the importance of adding organic matter to soil in lawns and gardens.

Lang says, “In general, five to 10 percent organic matter is considered optimal for healthy plant growth. However, most garden soils range from two to three percent soil organic matter.”

According to SDSU Extension, “Feeding soil a diverse diet of organic matter is an essential part of any management program. The secret to maintaining a balance between building organic matter and growing crops intensively is to add residues continually.”

“Mulching with organic matter,  adding compost and using cover crops – also called green manures – are the most common ways to add soil organic matter,” SDSU Extension continues.

As microbial populations and other insects and animals consume and decompose soil organic matter, a reasonably stable product known as humus is left.

“Humus consists of very long, hard-to-break chains of carbon molecules with a large surface area,” Lang says. “These surfaces carry electrical charges, which attract and hold nutrients plants need, making them more available to plants.”

Compost

“The gardener’s equivalent to nature’s humus production is the composting process. Compost is teeming with microbial populations, incorporating organisms from all six biological kingdoms throughout its highly diverse humic profile,” Lang states.

However, when adding compost to gardens, trees, shrubs and lawns, several essential considerations exist.

Although compost can vary in its nutrient content, as a general rule-of-thumb, compost contains nitrogen, phosphorus and potassium.

“Compost also provides other nutrients plants need in lower quantities, including calcium, magnesium and sulfur, as well as a wide variety of trace elements depending on the starting materials,” she says.

When applying compost to growing areas, SDSU Extension recommends using well-finished compost, which should be dark brown, fairly dry and crumbly and have an earthy smell.

“Compost which is not thoroughly broken down will use elements from the soil to finish its decomposition process before the minerals it contains will be available to plants,” Lang adds.

“This means microbes will feed themselves before sharing nutrients with plants, which will be a problem if not managed correctly.”

SDSU Extension suggests incorporating one to two inches of compost into the top few inches of soil before seeding or transplanting in existing beds for vegetables and annuals.

Gardeners can also apply a side-dressing of compost midway through the growing season as a water-retaining mulch and a source of slow-release nutrients for their food crops and flowers, she mentions.

Microbes

“While compost provides slow-release nutrients, gardeners will find an even better benefit from compost,” Lang says. “Microbes in particular, as well as beneficial bacteria and fungi are the organic grower’s number one defense against a variety of plant health issues.”

“Beneficial microbes are nature’s utility player for maintaining plant vigor, influencing drought resistance and nutrient uptake, defending against soil and airborne pathogenic diseases and producing plant growth hormones,” she continues.

According to SDSU Extension, microbes are important to plant survivability, as plants will secrete 20 to 30 percent of the food they produce through their roots to feed and attract microbes to the root region. 

These secretions, known as exudates, consist of carbohydrates, organic acids, proteins, exoenzymes and other substances. 

“The main benefit of these plant carbohydrate releases is they ensure microbial carbon – energy – needs are met. Microbes need a roughly 25 to one carbon-to-nitrogen ratio to meet growth needs,” Lang adds. “These needs can be met by their own decomposition of organic matter or through sugars exuded by their host plant roots.”

Nearly every known species of plant forms a relationship with several species of beneficial microbes. 

“Microbes can inoculate every area of a plant, from the root zone below ground, to the exposed, habitable plant tissue above ground and even tissue inside the plant as well. The job of these microbes is simple – protect and nourish the plant at all costs,” she concludes.

Melissa Anderson is the editor of the Wyoming Livestock Roundup. Send comments on this article to roundup@wylr.net.