By SHANNON HATHAWAY, Landscape Horticulturist and Sod Specialist
It is no secret that our native soil in central NC is not the best. When you purchase a new home, you usually find your soil consists of heavily compacted clay or sand. When you purchase an older home, you may have a light layer of topsoil, but the nutritional value is uncertain. The NC Department of Agriculture offers a soil test that is free of charge most of the year, and I strongly recommend you get your soil tested before determining what steps are necessary before planting grass, shrubs, trees, ornamentals, or vegetables. NCDA&CS Agronomic Division – Soil Test Forms and Information (ncagr.gov) After 25+ years in horticulture in NC, I have read countless soil tests, and the average yard has a pH of 4-4.5, an organic matter content (HM%) below 1%, and a cation exchange capacity (CAC) of 10 or lower.
What do these numbers mean? The pH, or soil acidity, for growing lawns should be 5.5-6.5 (does not apply to Centipede or St.Augustine), so most lawns require an annual lime treatment to raise the pH. Ideal HM% is 5%, meaning we must add nutritious organic material to improve the nutritional value of our soil. The cation exchange rate measures the soil’s ability to absorb nutrients and water, and then release them to the plant roots. The CAC correlates to W/V or weight/volume. In layman’s terms, CAC measures the compaction of the soil.
In order to grow anything successfully in central NC, we need to add “good soil”. There are many choices of soils out there, and shopping for soil can be very confusing. Let’s take an in-depth look at the options available at most soil yards.
Topsoil is the top layer of soil that can be scraped up off a work site before construction and grading begin. While topsoil can improve drainage, there is usually little or no nutritional value in it. It is inert, meaning it does not cause or promote change or growth. You can buy topsoil screened to remove roots, rocks, and debris, or unscreened. Either way it is best used as fill-dirt or structural soil, and will not improve the soil’s ability to grow anything.
50/50 means 50% topsoil and 50% compost. The topsoil acts as a fill and improves drainage. The compost improves the nutritional value of the soil, increasing the pH, the HM%, and the CAC mentioned above. This mix is excellent as a base for sodding or seeding.
Landscape Mix is a blend of composted woody soil amendments and compost. It is soilless and an excellent soil conditioner for clay soils. This is an excellent product for building garden beds, vegetable beds, or establishing a nutritious base for sod or seed. Landscape mix is high in nutritional value, and improves drainage, pH, HM%, and CAC. Think of it as healthy food for your plants. It can be worked into the soil, or layered on top of loose base soil. I build my soil layers like nature does, adding compost and composted woody amendments to the top each year. At this point, I have rich black earth 6-12 inches deep on most of my land. It takes time and hard work, but the results are amazing.
Pure compost consists of a combination of green and brown materials – vegetative matter and woody matter – piled together and given time to break down to form rich, black humus matter. This is an organic process that requires sun, rain, worms, and beneficial microorganisms to work together over time. Compost that is mixed or turned frequently will decompose more quickly. When cow manure, chicken manure, or horse manure is added in large amounts, the compost can burn plants if used undiluted. Manure-based composts should be worked into the soil in small amounts, not used as planting soil. Compost that is low in manure content can be safe for direct planting, so make sure to ask about the content of compost when shopping.
Of course the prices of these products can vary depending on the quality of ingredients, the packaging, and the cost of delivery. As with everything, quality matters. Ask questions, and choose a reputable soil vendor. I’d like to thank Soil Toppers in Fuquay-Varina for their information and input. Soil | Soil Toppers If you still have questions, please let me know. firstname.lastname@example.org