The scoop on soil

New homeowners, first-time gardeners — anyone who’s planted gardens and coddled new lawns and trees — may feel they’ve gotten a dirty deal when the shovel was practically sucked out of their hands by a sticky, wet clay.

That so-called soil would be great for producing flowerpots, not so great for producing flowers.

In newer residential developments especially, topsoil often is the first thing to go before a house goes up. When construction ends and the lumps and bumps of the site are smoothed out, a green blanket of sod goes down.

And the soil? Gone.

Except where builders have returned topsoil to the site, many homeowners will need to address what’s underfoot before starting to plant.

“It’s better to do that on the front end,” said Marti Neely, a landscape designer for Mulhall’s in Omaha. “It’s an investment in plant success.”

After a killing freeze and the garden has been cleaned of all plant material, fall is a prime time to start a soil makeover.

The good news is, “most soils in Nebraska are pretty good,” said Charles Shapiro, a soil scientist with the Haskell Agricultural Laboratory in Concord, Neb., near South Sioux City.

When soil particles fell from volcanoes to the west, an organic material layer formed. “So the soil had some structure,” Shapiro said. “That’s topsoil. It was 18 inches deep before we broke sod.”

A layer that was thousands of years forming can be quickly removed at a construction site.

“Homeowners want to create 10,000 years of topsoil in two weeks,” he said.

Taking a soil sample is a good start, but even soil scientists know many or most homeowners will just throw on some fertilizer and hope for the best. The risk in that is overfertilizing.

However, the homeowner doesn’t have to be clueless. A visual inspection can usually identify soil that’s alive or dead, Shapiro said.

“You can easily see, if it’s hard to dig a hole or if it’s compacted and water and air can’t get in. Microbes need air, water and carbon.”

Areas where water doesn’t drain also are physically bad.

It’s a good sign, on the other hand, when you see soil that’s the color and texture of a moist brownie mix. It’s crumbly, dark and probably contains some bits of wood or leaves.

To see the difference, Shapiro recommends comparing soil from the foundation with that of an established flower bed. The foundation soil will likely be compacted, even white from the mortar or lime of the concrete foundation and footings. A flower bed, usually amended in some way, will be darker, and not powdery dry, too sandy or too compact like a fistful of clay.

Another commonplace problem in new developments, Shapiro said, is a tree dying after only a couple of years.

It’s often the result of compaction, or the hardpan layer, as some call it, which can be 2 feet down, he said. “When roots get there, they don’t like it.”

That’s a hard problem to solve — one answer is to plant something that will grow there, such as ornamental grasses, or shrubs or even a tree that can take that inhospitable environment.

A clay soil is hard to change.

“There’s a limit to what you can do,” Shapiro said. “This soil is like a loose sponge cake. Once compacted, it’s hard to uncompact it.”

On the other hand, “if you dig up soil and it breaks apart fairly easily, that’s tilth. You can feel it.”

Tilth is a measure of the health of soil. Good tilth refers to soil that has the proper structure and nutrients to grow healthy crops. Soil in good tilth is loamy, with a healthy balance of sand, clay and organic matter.

It’s soil that’s alive, said P. Allen Smith, a Little Rock, Ark., nurseryman and host of “Garden Home” in its ninth season on TV. He was a lecturer at the Lauritzen Gardens’ annual Antique and Garden Show last week.

“You want living soil. There’s a very complex community going on there — of worms, mycorrhizae (a fungus-root association) and beneficial fungi.”

As for topsoil in his rocky Arkansas soil, “We stockpile it. We take off a layer of soil, carry away the subsoil and return the topsoil. I’m greedy about topsoil.”

Contact the writer:

444-1059, rhonda.stansberry@owh.com

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