We’ve had questions lately about soil and compost. Apparently there are lots of folks who think they are the same thing, but there’s a big difference.

Soil is basically the top layer of the earth. Soils are made up of various proportions of sand, silt, clay and small amounts of organic matter (decaying insects, plants, creatures, fungi), as well as minerals and nutrients. These different-sized particles give soil its texture.  It is  the natural medium in which to grow plants. A publication  from the Environmental Protection Agency says there are more than 70,000 types of soil in just the United States. Just don’t call it dirt. Dirt is is mainly ground rock and pebbles; a filler with mainly mineral content but no real nutrients. Dirt smells and looks like dust. Soil is dark and smells earthy.

Soil formation happens when many things interact: air, water, decaying plant life, rock, animal life and chemicals. It forms over a period of up to 1,000 years.  Plant roots and lichens break up rocks, which become part of new soil and roots loosen the soil and allow oxygen to penetrate it. Also, earthworms and other organisms live in soil and help loosen or aerate it. If you’re creating new in-ground garden beds or building a raised-bed garden, you’ll need to amend the native soil and in some cases add soil. That’s where compost becomes important.

Compost is the recycling of plant and kitchen waste as a fertilizer and soil amendment. It is dark and crumbly and, when done correctly, smells like good soil. Compost improves soil and plants  by returning organic matter to the soil in a usable form. Compost helps break up heavy clay soils, improving its drainage. It makes sandy soil better able to retain water and essential nutrients. Adding organic matter (compost) to soil improves plant growth and is essential  for gardens in the Sonoran desert. Improving your soil is the first step toward improving the health of your plants, but compost is not a planting medium; it is a terrific soil amendment.

You can make compost at home, easily. Or you can purchase organic compost at Southwest Gardener or reputable nurseries. If you’d like to start a home compost  pile, chapter 6 of “Desert Gardening for Beginners” tells you all you need to know to be successful.