, Port Arthur, Texas


September 24, 2012

Soil Amendments and Conditioners

PORT ARTHUR — Even as an avid gardener I never paid close attention to all the pallets of soil amendments stacked up at the home improvements stores. Occasionally, I would grab a bag of potting soil or cheap compost that was on sale but never paid much attention to the other bags of “stuff.” Researching, I found there are some interesting options available to help Southeast Texas gardeners.

Peat moss is used to add organic matter to the soil, loosen, or aerate. When worked in well, it does a good job of breaking up clay soils. Peat moss is acidic and since some clay soils are also acidic it can hurt some plants. Many people add dolomitic lime to bring down the acidity. Be cautious, a few tablespoons of lime will bring down the Ph of a big bag of peat moss. Peat moss is low on nutrients, so, is usually used in conjunction with other amendments or fertilizers.

Top soil is taken from the top few inches of soil. When you buy it in the bag, many times, it is just a mixture of organic matter, loam, silt and clay. It is generally a good amendment for any soil.

Perlite and vermiculite are minerals and do not add any nutrients to the soil so are only used to help aerate and absorb moisture. Their mining process sterilizes them making them great for use in potting soils.

Potting soil is usually a mixture of peat moss, perlite, vermiculite, compost, and fertilizers. It is very friable to allow roots to easily grow but does not have enough body to support a full grown vegetable plant. Usually you start your plants in potting soil and when big enough you transplant them in another pot with soil or directly into the ground.

Mulch can be many things such as freshly ground up wood shavings, different kinds of bark, or mixture of all kinds of organic matter. One thing it is not is decomposed.  Mulch should not be added directly to garden soil. Since decomposition requires nitrogen, if you bury mulch in your garden it will pull nitrogen from the soil and rob it from your plants  Mulch should be put on the surface to slowly decay and retain moisture.

Compost is decayed organic plant material and one of the best amendments.  Special attention should be taken when buying compost in a bag. Most commercial composts are made from one type of base material such as wood products, spent hops, or corn stalks. This fine but the best would be to mix 2 or 3 bags of different types of compost to get a wide variety of nutrients. This is why home composting is usually the best since it will have a wide variety of decayed materials.

Tim Schreck is a Jefferson County Master Gardener. Reach him at or call Texas AgriLife Extension office 409-835-8461.

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