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Soil Amendments for the Garden

submitted by Sarah Browning, UNL Extension Educator

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How did your landscape do last summer? Not so good? Maybe it's a soil problem, because no matter what type of plants you are growing- flowers, vegetables, fruits or turfgrass- soil is an important key to success. Often existing garden soil is not ideal, being too compacted, too heavy, too porous (sandy) or too alkaline. Soil amendments can help with all of these problems by improving soil's water-holding capacity, drainage, increasing nutrient levels and modifying pH level.

What Are Soil Amendments?

A soil amendment is any material mixed into the soil to change one of these characteristics- compared to mulch that is applied on top of the soil. Mulches are used to moderate the soil temperature, prevent weed growth and reduce soil moisture evaporation.

A soil amendment can be either an organic or inorganic product. Organic amendments come from something that was once living like leaves, wood chips, wood ash, grass clippings and peat moss. Compost is also an organic soil amendment, consisting of decomposed leaves, grass clippings, etc. Inorganic amendments originate from inanimate sources, and may be processed further by man. Common inorganic amendments include sulfur, lime, vermiculite, perlite and sand.

Not Recommended...

However, not all soil amendments are recommended for Nebraska soils. For example, wood ashes are high in salt and pH, something our native, alkaline Nebraska soils don't need. Don't be confused by the fact that farmland often becomes acidic over time and requires amendment with lime to raise soil pH. The same is not true for home landscapes.

Sand is another soil amendment, that sounds good in theory but doesn't work well with heavy Nebraska clay soil. When sand is added to clay, the particles clump together very closely and instead of lightening the soil, creates a texture similar to concrete. Gypsum is another soil amendment commonly discussed by homeowners, but should only be used on soil with high levels of salt; it is not effective to "sweeten" soil or lower soil pH.

Increasing Organic Matter

Many garden soils are low in organic matter, often only 1-2%. 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 by sandy soils, thus reducing the frequency of watering required. As organic material breaks down, it provides nutrients for plant growth. Fifteen percent organic matter is ideal for vegetable gardens, but it may required several years of soil amendment to reach this level.

Adjusting Soil pH

Soil amendments can also used to change the soil pH level. Many Nebraska soils have a pH level ranging from 6.5 to 7.5 or higher. Ideal levels for vegetable production are pH 6-7. To lower soil pH levels, elemental sulfur or aluminum sulfate should be applied; however, large amounts of sulfur are required to make even a small change. For example, a loam soil with pH 7.5 requires 15-20 pounds of elemental sulfur per 1000 sq.ft. to reach soil pH 6.5. Lime is used to raise the soil pH and is usually not needed in Nebraska soils; apply lime only to soils with a pH below 5.5. Before making any adjustments to your soil pH, do a soil test to determine the existing level.

This resource was added March 2011 and appeared in the Lincoln Journal Star Newspaper Sunday edition. For information on reproducing this article or using any photographs or graphics, read the Terms of Use statement