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Gardening: Soil quality is key for optimal growing

Robert Flowers (right), Sharon Bowman and Machelle Harris mix and water down a new compost pile at a recent Master Gardener training class Saturday at the Spokane Conservation District’s Green Zone at North Havana Street. Adding compost to your garden soil is the best way to improve its texture and level of biological activity. (Pat Munts / The Spokesman-Review)
Robert Flowers (right), Sharon Bowman and Machelle Harris mix and water down a new compost pile at a recent Master Gardener training class Saturday at the Spokane Conservation District’s Green Zone at North Havana Street. Adding compost to your garden soil is the best way to improve its texture and level of biological activity. (Pat Munts / The Spokesman-Review)

Most gardeners think we just grow plants; lots of pretty and tasty plants. But do you want to know something? It’s the soil that makes all those pretty plants happen. Yep, we are soil gardeners first and plant gardeners second. Or so we should be thinking about gardening in that light.

But if you aren’t a soil scientist, how can you tell what kind of soil you have and how well it will support your plants? The WSU Spokane Master Gardeners have developed a couple of simple tests that can help you determine the type and quality of your soil right in your own backyard.

First, is your soil sandy, clayey or loamy? This will help you determine how well the soil will hold water and nutrients. Sandy soil doesn’t hold nutrients or water as well as loamy soil. Clay soil doesn’t drain well and may be too dense for some roots to grow in. Loam holds nutrients and water well while draining away excess water.

To determine your soil type, add a heaping cupful of soil to a quart jar and fill it with water. Cap it tightly and shake it for a minute and then let the jar sit until the water is clear and the sand, silt and clay have settled into distinctive layers. The bottom will be the sand particles followed by silt with the clay particles as the top layer. If the soil has a lot of organic matter in it, that will be floating at the top of the water.

Measure the thickness of each layer and then divide each measurement by the total depth of the soil. This will give you a percentage; a higher percentage of sand means your soil is sandy while a higher percentage of clay means it’s a clayey soil. Close to equal percentages mean you have a loam, the best kind of soil.

To check how biologically active your soil is, count the number of earthworms you turn up in a cubic foot of soil. Wait until the soil temperature is at least 55 degrees and is damp but not sopping wet. Place your measure of soil in a wheelbarrow or on a large piece of cardboard. Sift through it counting the worms as you go. Ten worms means the soil is active and the more worms the better. Not only does this mean that there are enough organisms to keep the worms fed, it also means the worms are doing a good job of aerating the soil.

Regardless of the results of either of these tests, the simple way to improve soil texture and raise biological activity is to mix lots of compost into the soil. Your soil has enough compost when it is a dark chocolate brown color. Compost can be made at home with your own garden debris, purchased at garden centers or in bulk from local soil supply companies. Early spring and late fall are the best time to add compost to your soil.

Pat Munts has gardened in the Spokane Valley for over 40 years. She is co-author of “Northwest Gardener’s Handbook” with Susan Mulvihill. She can be reached at pat@ inlandnwgardening.com.


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