When I chose my home, my biggest concerns were affordability and good schools for my children. Only years later, as I struggled to figure out my garden’s weird soil, did it occur to me that I should’ve paid more attention to what was under the bluegrass.
My soil is mostly silt loam, which sounds better than it actually is. Silt loam consists of only sand and silt. There’s no clay to help retain moisture and no organic matter whatsoever.
Kelly Grummons of Timberline Gardens had more sense. When he looked for a home, first he studied a soil map. After marking all of the neighborhoods in the Denver area built on clay loam, he presented the map to a real estate agent, eventually settling for a small house on a large piece of property with soil that would make a farmer gleeful.
Grummons may have won the soil lottery, but both of our gardens host plant nerds’ menageries with hundreds of plants. Soil type is definitely a case where one size does not fit all the plants we want to grow.
Just the same, most gardeners prepare their soil as if they were getting ready to sow an agricultural crop. First leveling their entire property, they add various amendments and till to an even depth and tilth throughout. Their goal is “chocolate cake” soil — dark, crumbly, rich in humus, and moisture-retentive — the stuff that vegetables adore.
Plants from meadows and tallgrass prairies, where fertile topsoil can be more than a foot deep, feel right at home in such a soil. But those that evolved to live in rocks, sand and the high- mineral soils of the interior West do not. Many appear ecstatic as seedlings quickly morph into massive specimens unlike anything you’ve ever seen in the wild. But too often, overindulged dryland plants don’t fare well in the long run. Their lifespan can be significantly shortened.
It turns out that my soil, without any amendment whatsoever, suits a large number of native plants, including prairie coneflower, dotted gayfeather, hairy gold aster, scarlet globemallow and silver lupines, as well as English lavender, catmint, basket- of-gold and many other exotics that prefer a lean diet.
If you want to grow a wide range of plants, the best philosophy is to treat each area of the garden separately. For vegetable gardens, flower beds of traditional annuals and perennials and lawns, regardless of existing soil type, Grummons recommends adding up to 30 percent by volume of a good quality vegetable-based compost (the kind made from recycled yard waste) and tilling it in 6 to 8 inches deep.
For xeric plantings in sandy, clayey or silty soils, Grummons uses 10 to 15 percent vegetable- based compost and 30 to 50 percent squeegee, pea gravel, expanded shale or small volcanic rock, tilled in 8 to 12 inches deep.
The payoff is obvious. This gritty, well-drained mix grows some of the best Western dryland plants in the metro area. For similar results, don’t treat every bed on your property as if you were planning to grow tomatoes.
Marcia Tatroe is a garden writer and lecturer. Her most recent book is “Cutting Edge Gardening in the Intermountain West,” ($29.95, Johnson Books). E-mail her at rltaurora@aol.com.
