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Gardening Q&A: Soil amendments are key for a home garden

Ray Ridlen advises readers about gardening and horticulture.
BY RAY RIDLEN, For The Oklahoman Published: March 18, 2013
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Lime is used on acidic soil to raise pH. Always base your addition of sulfur or lime on soil test recommendations, rather adding products on a hunch.

However, not all soil amendments are recommended for our soils. For example, wood ashes are high in salt and pH, something our alkaline soils don't need, and sand added to heavy clay soils creates a texture similar to concrete. Gypsum is another soil amendment commonly discussed by homeowners to “sweeten” soil or lower soil pH, but in fact it does neither and is seldom a helpful amendment for our soils. Gypsum should only be used on soil with high levels of salt, where it can bind with the salt molecules and aid in moving them out of the soil profile.

Benefits of organic

Organic matter supplied by organic amendments improves soil growing conditions in the landscape and garden. Adding organic matter to the soil increases pore space, creating a lighter soil that drains more quickly, allows better oxygen penetration for root growth, and is physically easier for roots to grow in than heavy compacted soil. Organic matter also increases water retention in sandy soils, thus reducing the frequency of watering required. Finally, as organic material breaks down, it provides nutrients for plant growth. Many of our soils are low in organic matter, often less that 1 percent. For a vegetable garden 15 percent organic matter is ideal for optimum root development and vegetable production. However, it will take many years of soil amendment with organic matter to reach this level.

Ray Ridlen is an agriculture/horticulture educator for the Oklahoma County Extension Service. For more information, call 713-1125.