Knowing the soil improves garden success

  • Posted: Friday, January 4, 2013 6:04 a.m.
A map showing different soil types in Rowan County.
A map showing different soil types in Rowan County.

SALISBURY — Beginner gardeners often complain about Rowan County soils. Popular television programs often depict gardens with rich, workable soils able to grow almost any vegetable or flower. Unfortunately, Rowan soils are extremely diverse, ranging from deep sands to slinky clays. There are 10 major soil types; clay soils are the most prevalent.

The biggest misconception about clay soils is they are poor and non-productive. Observing large growth of trees and tons of vegetables per acre easily quells the myth about the lack of plant growth in these soils. The most experienced gardener will confess that tight clay soils are difficult to manage; however, with proper modification, these soils can easily produce both ornamentals and garden vegetables.

Clay soil texture can be improved by amending the soil to improve drainage and oxygen. The best amendments for clay soils are pine bark humus that is less than 1/2-inch in diameter, composted leaf mold, or Permatil. Permatil is a manufactured natural amendment made from slate rock, heated to expand and provide pore space as an amendment for tight clay soils.

Make sure that leaf mold or compost is fully composted and not merely “aged” before adding the soil. Uncomposted materials that are not fully decomposed compete with plants for nutrients, especially nitrogen and sulfur, resulting in nutrient deficiencies and poor plant growth.

Peat moss, sand, hardwood bark, sawdust, wood chips and pine straw are not recommended as an amendment for clay soils. Addition of these materials does not adequately improve the physical properties of a clay soil; in fact sand added to clay makes the soil more like a brick.

Amendments to clay soils must be incorporated to at least 25 percent by volume to be effective. For example, to result in approximately 8 inches of amended soil, a minimum of 2 inches of the amendment should be incorporated into the top 6 inches of soil. This also helps raise the bed which will not only improve drainage but will also make bedding plants look more attractive. Incorporating up to 50 percent by volume will probably improve plant growth. Incorporating more than 50 may have a negative effect on plant growth, while incorporating less than 25 percent by volume is a waste of time and material.

It’s important to plant a cover crop as soon as the soil is workable. Cover crops such as rye grain, wheat, crimson clover or oats reduce erosion and supply much needed organic matter. Cover crops should be plowed under as green manures in late winter or early spring, six weeks before planting. These crops produce an abundance of biomass that improves the tilth (workability) of the soil.

Darrell Blackwelder is the county extension director with horticulture responsibilities with the N.C. Cooperative Extension Service in Rowan County. Call 704-216-8970.

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