September 12, 2008

The Dirt Gardener: Soil Amendments

By Buzz Bertolero

Q: What is the difference between compost, soil conditioner or amendments and topsoil? This gets very confusing since there are so many different varieties and brands. Is one better than another?

A: Yes, it is easy to get confused. They're often referred to interchangeably.

Soil amendments and conditioners are divided into two types -- organic and non-organic. Organic soil amendments/conditioners include peat moss, wood products, animal manures, compost and other organic matter.

In clay soils, they improve texture and structure for drainage and aeration. The soil microorganisms then break down the organic matter into nutrients that plants can use. Hence, in seasonal planting areas such as vegetable gardens and flower beds, they are replenished annually, while with permanent plantings, they're added at the time of planting.

Non-organic products include perlite, vermiculite and sand. Sand is not recommended as a soil amendment, as it only compounds the heavy clay soil issues. Perlite and vermiculite are normally not used in outdoor plantings, because of the cost.

Unless moisture retention is crucial, peat moss is not recommended, as it holds too much moisture.

The original soil conditioners were lumber mill byproducts. The predominate brand from the late 1960s through the early 1990s was Redwood Soil Conditioner. It was inexpensive to produce and was close to the marketplace, so transportation costs were reasonable.

As the supplies of the raw material became scarce, the product changed. Today's soil conditioners are a blend of many different types of organic matter.

I believe that today's many brands are superior to the original because of the addition of oyster shell lime, kelp meal, bat guano, animal manures, worm castings and others organic matter.

Compost comes from composting, which is the process of breaking down or changing large particles into smaller components. It is also used to improve soil texture and drainage.

Homemade compost consists of a combination of "brown" and "green" ingredients, including grass clippings, plant trimmings and kitchen wastes.

Commercial products probably contain no grass clippings or kitchen wastes. The distinction between commercial soil conditioners and compost becomes more of a marketing issue, as they are very similar.

The classic definition of topsoil is the surface or upper layer of soil that is rich in organic content. It takes years to develop, but these days, it often gets scraped away during housing construction.

Today, topsoil is a lower-grade product that is used to fill in depressions or to raise the grade. Unfortunately, it has little organic matter and should be amended as plants struggle to grow in it.

It is less expensive when compared to all the other options, so that should be a dead giveaway as to its value.

Soil conditioners, amendments and compost are designed to improve existing soil, while topsoil is used to replace the soil that has been lost.

In making a selection, decide what your garden needs and then purchase the product that fills that need.

Price alone shouldn't determine what is the best. If you need more help, the nursery professional at your favorite garden center is a great resource.

Buzz Bertolero is executive vice president of Navlet's Garden Centers and a California Certified Nursery Professional. His Web address is, and you can send questions to [email protected] or 360 Civic Drive, Suite D, Pleasant Hill, CA 94523.

Originally published by Buzz Bertolero, The Dirt Gardener.

(c) 2008 Oakland Tribune. Provided by ProQuest LLC. All rights Reserved.