Garden Variety: Healthy soil composition key for healthy plants

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Building and maintaining healthy soil is one of the most important steps in growing healthy gardens, landscapes and lawns and is often overlooked or considered as an afterthought. And, the best time to build and improve soil is prior to planting, making this late winter-early spring season the perfect time to prepare new planting spaces for spring. Existing gardens, landscapes and lawn will likely also benefit from soil improvement this time of year.

Soil is more than the particles that are often referred to as “dirt.” Soil contains a blend of sand, silt and clay particles; organic matter; air; water; nutrients; and microorganisms. The composition of all these things put together affect the way water and air move through the soil, how roots grow, and how many nutrients are available to plants.

The single best thing you can do for soil (for the types common in northeast Kansas) is add organic matter. Compost is a type of organic matter that is easily incorporated into the soil and readily available. Compost loosens heavy clay soils, allowing for better air and water movement and root growth. In sandy soils, compost improves fertility and water-holding capacity. Compost contains small amounts of nutrients that benefit plants and create a more favorable environment for beneficial microorganisms.

For new gardens, landscapes and lawns, spread one to three inches of compost over the area being prepared and till or otherwise mix the compost into the soil.

For existing gardens and landscape beds with perennial plantings, apply up to one-half inch of compost over the root spread of the plant. In bare areas around the plantings, spread compost and work it into the soil with a trowel, shovel or other tool. For lawns, core aerate, then apply up to a half-inch of compost over the entire area. The practice of spreading compost in this manner is called topdressing.

Soil tests are also beneficial. Take soil samples and submit them a few weeks prior to adding compost so that other improvements can be made at the same time. Basic soil tests show soil pH and levels of phosphorus and potassium. More advanced tests can determine organic matter content, micronutrient levels, and some types of nitrogen.

Soil samples can be submitted for testing at the Kansas State University soil test laboratory through K-State Research and Extension local county offices. Tests typically range from $8-$20 per sample depending on the county and requested analysis. They will also provide recommendations for soil improvement. There are also private labs that perform soil testing and home test kits. The downside of home test kits is not knowing what to do with the results.

Soil pH is especially important because it affects the availability of nutrients to plants. A good example of this is with pin oaks in this area. The leaves of these trees are often pale green to yellow — a condition known as iron chlorosis. The issue is typically caused by high soil pH that prevents uptake of iron, rather than by an iron deficiency in the soil. Lowering soil pH without disturbing tree roots is a momentous task.

Organic matter should be added on a regular basis. In nature, this happens as leaves fall to the ground and plants die back to the ground. Mowing leaves instead of raking them in the fall is a good way to return organic matter to lawns. Leaves and other plant material can also be left in landscape or garden beds and worked into the soil as they decompose.

For garden beds that are planted annually, consider the use of cover crops in the fall and winter. Cover crops are plantings made specifically to cover the soil and provide organic matter than can be incorporated into the soil. Annual rye grass is a common cover crop because it germinates quickly and is readily available.

— Jennifer Smith is a former horticulture extension agent for K-State Research and Extension and horticulturist for Lawrence Parks and Recreation.


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