Improving Garden Soils with Compost

By Tom Tharp, St. Louis Composting

It’s early spring, time to plan and prepare for garden bed planting. Unfortunately, while most of us consider what floral plant, colorful shrub, or a variety of vegetables we’d like to try in our garden spaces this year, some gardeners neglect to consider the one thing that helps make a great garden happen— good, healthy soil.

Soil is the common thread between a row of carrots and a row of handsome oak trees lining a drive. Soil supports the plant by allowing its roots to penetrate and draw moisture and nutrients to make plants thrive.

Before the first seed or small plant goes into the garden bed, consider a simple improvement to help your plants perform better. Apply and blend compost into the soil before planting.

Compost contains abundant benefits to soils depleted with last year’s growth and vastly improves poor native soils. Compost contains organic matter, which helps modify a soil’s structure, allowing moisture and plant roots to penetrate hard, compacted soils. Organic matter affects soil structure by changing the soil particles’ composition. Silt and clay soils, which are predominant in our area, have minute particles of all the same size that lock themselves together, like bricks in a wall. Organic matter helps break up the pattern of the particles, allowing moisture and plant roots to penetrate much more easily.

Additionally, higher organic matter content helps soil work better in both the wet and dry cycles of weather we have here in the Midwest. Organic matter helps moisture better enter the soil and helps it hold more moisture during dry periods. Further, it helps absorb moisture and allows it to pass deeper into soils during those wet periods.

The pro’s tip is to spread 1-2” of compost over the garden bed when the soil is fairly dry, then spade or till compost into the top

6-8 inches of the garden area, breaking up large clumps. Drier soil has less of a tendency to form those clumps, so compost can be blended in more successfully. The ultimate goal of any healthy soil is to achieve at least 5% organic matter. The “Strive for Five” slogan is something to remember when amending your soils.

In addition to providing organic matter, compost contains a wealth of soil microbes. The bacteria and fungi present in compost colonize in local soil, adding the ‘life’ that most poorer soils lack. The microbes help the soil and the plant work together to form strong roots and exchange nutrients, making the plant more vigorous and resistant to soil-borne problems.

Although compost is not considered to be a fertilizer in the conventional sense, compost is a nutrient-rich amendment for soils. While nitrogen, phosphorus, and potassium (N, P, and K) are considered the ‘big three’ of plant nutrients, there are other plant nutrients present in compost. Minerals like sulfur, calcium, iron, and a host of others needed for optimum plant health and growth, are present in compost. These nutrients help build plant cells and are vital in producing the most healthy and vibrant plants. Conversely, the absence of minor nutrients can cause a number of plant health issues, including chlorosis (yellowing), leaf spotting, leaf tip browning, and curling, etc.

While these nutrients are necessary for the soil, an additional dose of the big three nutrients is often required to push plants to the next level. Organic and non-organic fertilizer solutions are available at all home and garden centers. In short, compost offers a way to improve the soil and the plants growing in it through its multiple attributes. Improve your gardening success with a bit of preventative action. Improve your soil with compost!