Monday, May 30, 2011

Here's the Dirt: on Soil, Compost and Mulch - Introduction

When you go to a garden center, you'll find lots of bagged goods with names like potting soil, planting soil, top soil, bark, fine bark, play chips, compost, mushroom compost, planting compost, etc. There's chicken manure and steer manure and bat guano (more manure). Some companies sell three-way and five-way mixes of various ingredients that claim to be excellent growing media.

With so much available, how do you choose which, if any, of these products are right for your garden? The first step is to understand what these materials really are. There's a lot to say about some of them, so I'm going to do a series of posts to tell you about soil, soil amendments, compost and mulch.

First up - soil. 
Soil, also called dirt, is the foundation of your garden. The health of your soil determines the health of the plants you grow. If you are at all serious about gardening, particularly if you plan to grow some of your own food, you owe it to yourself to learn about the soil you have and how best to maintain its tilth or health.

Technically, soil is a combination of sand, silt and clay particles with some amount of organic matter mixed into it. There is no precise recipe for soil. The soil you have is the product of the wind, weather and geology of your area.

Thanks to the action of glaciers long ago, soils in the Seattle area are varied. Some of you are gardening in sandboxes. Some of you are trying to break up clay. If you are gardening in an area along a river, you might have silt. Many of you are finding rocks the size of your fist nearly everywhere you dig. All of these scenarios are the gifts of what is called "glacial till."

The combination of sand, silt and clay particles you find in your garden is what makes up the structure of your particular batch of soil. Organic material comes and goes over the seasons. Nutrients and water are taken up by plants. Depending on the health of your soil, microscopic organisms thrive or struggle. Through it all however, year after year, those sand, silt and clay particles remain, providing the stage where all the rest is played out.

There are many things you can do to improve your soil, but there is nothing you can do that will change the type of soil you have. A clay soil, for example, cannot be changed into sandy loam, no matter what you add to it. (In fact, as I'll explain in a later post, adding sand to clay is a bad idea.) Your best bet is to know what type of soil you have, what its characteristics are and how to make the most of what you have.

In Part 2 of "Here's the Dirt," I explain more about soil types.
Wondering how much mulch, soil or compost you should buy for your gardening project? Check out this handy table