Rock Gardens: Find the Best Stone for Your Rock Garden

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“Rocks are the bones of the garden,” says Martin Mosko, founder of Marpa and Associates in Boulder, Colorado. “Like bone, rock doesn’t change, but when you place ephemeral elements such as plants or water next to the unchanging structure of stone, it creates magic in the garden.”
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Blending stone with water elements such as streams and fountains incorporates the concept of yin and yang. “The interplay between water and rock is like male and female,” Mosko notes. “Both are powerful in their own way, and you need both to create a balanced garden.”
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“When landscaping with rocks, be mindful that you’re stealing them from the earth, so you should regard them as precious and use them respectfully,” says Mosko.
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“Rocks are the bones of the garden,” says Martin Mosko, founder of Marpa and Associates in Boulder, Colorado. “Like bone, rock doesn’t change, but when you place ephemeral elements such as plants or water next to the unchanging structure of stone, it creates magic in the garden.”
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“Make your microcosm match the macrocosm,” advises Mosko. “Cobblestones are delightful in medieval European villages, but they wouldn’t look very good in the desert Southwest.” Marpa and Associates sources stone from within the state whenever possible to minimize handling and transportation.
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Pick the best stone for your garden.

What could be a more appropriate landscape material than rock? It looks natural in any environment–from the Arizona desert, where it can be the focal point of a dry garden, to the Northeast, where stacked fieldstone walls and blocky granite steps are visual treats, to the Rocky Mountain West, where boulders hint of the surrounding grandeur.

Stone (the preferred term in the trade) is used in landscapes for both aesthetic and functional reasons. Functionally, stone defines a structure with walkways, walls, patios, and even water features. Aesthetically, stone anchors the landscape and provides year-round interest. And, wherever you are, attractive and serviceable stone is readily available. Sandstone, granite, limestone, and slate are common in landscapes, but even marble and volcanic scoria–lava cinders–can be used for a home’s exterior. The only stone no-no is alabaster; it wears away too quickly in the rain.

In areas where drought is a problem–and almost no region of the country seems to be immune these days–landscaping stones reduce the amount of irrigation required. Whether stone is used as a gravel mulch, to build a patio, or in a cluster of large boulders, less mowing and trimming are required–a savings on fuel and fumes.

That’s a lot of rock-solid pluses. Even so, there are a few environmental issues you’ll want to consider before getting started. Is there enough of the stone left in nature? How is it harvested? And, most important, how far was it transported?

Get to know your stone

When you’re scouting for landscape rock, visit local stone yards (look under “Stone-Natural” in the Yellow Pages). You’ll quickly learn that “a rock is a rock is a rock” just isn’t true; the array of choices is mind-boggling. While your decision will be guided by your home’s look and the stone’s purpose, you’ll also want to ask these questions.

• Where was the stone quarried and how far has it been shipped? Fossil fuels are used to quarry, mill, and ship stone–and with a material as heavy as stone, that’s no small concern. The closer the stone is to home, the better.

• What is the quarry’s track record on reclamation? Quarrying is permitted only after a reclamation plan has been approved. To reclaim the land, any leftover scraps are pushed back into the ­­­­hole, followed by dirt removed from the next hole. Topsoil and seed complete the job. The end result may be a change to the terrain, but there should be no gaping holes or barren patches.

• Was this gravel or rock mulch mined from a riverbed or elsewhere, or crushed to this size? By choosing crushed rock, you’re probably using a byproduct from a quarrying operation.

• How porous is the rock? In some applications this doesn’t matter, but for a wall where freezing and thawing could cause damage, you’ll want to know. Lightweight volcanic stones and limestones are more porous than most.

• Is it an acidic or basic rock? Limestone may make a water garden too alkaline, and it also can be degraded by acid rain.

• How big must an ornamental boulder be? For the backyard of a modest neighborhood house, a half-ton boulder might fit nicely; on the grounds of a ranch, a ten-ton boulder would be suitable. Plan on burying at least a third of the boulder, or bury it up to the line that the boulder was buried to in its natural setting.

• Will this stone look right in my yard? Many landscape designers prefer to work with native stones that fit the region’s cultural typography. An outcropping of red sandstone in the “Granite State” of New Hampshire or a slate patio in the Southwest might look a bit odd.

Throwing stones

“There are huge reserves of stone in the United States and throughout the world,” says Jim Lardner, president of the industry association Allied Stone Industries and vice president of New Mexico Travertine in Belen, New Mexico.

While that’s what was said about the passenger pigeon and the bison, it seems to be true with stone. There are no “Save the Stones” campaigns, although some popular areas are being stripped of petrified wood and individual quarries do get played out.

Getting stone from the earth to the stone yard isn’t entirely painless, however. Whether the stone is simply scooped from the earth with a front-end loader (as is the case with river rock and some light volcanic rocks) or quarried by hand, sawing, or blasting, it’s a major industrial operation. At the end of the process, there’s nothing much left but a hole–and that must be reclaimed.

The bottom line? “There are always going to be individuals who think that because we’re moving dirt around, we’re raping the earth. But my contention would be that the way we’re doing it these days, we’re just changing the contour of the ground by five to six feet,” says Steve Bayer of Bayer Stone in St. Marys, Kansas.

Does moss matter?

Is moss rock worth the extra price? In the West, “moss rock” has a certain cachet. The “moss” is really a lichen–a mix of fungi and algae–that lives on any kind of rock. When the boulders are moved to residential settings, the lichen is almost sure to die; either irrigation water or pollution from the street kills it. “It’s a waste of your money to pay higher prices for lichened rocks,” says botany professor emeritus Bill Weber of the University of Colorado. “Buy the rock for the rock itself; forget about the lichen.”

Quarry neighbors might say there is more to it than that–including erosion, dust, and noise from heavy trucks passing by. In fact, those trucks and other equipment used in quarrying are the biggest source of environmental concern.

You may be able to avoid some of that trucking. Consider using foundation boulders (rocks that are removed to make way for a basement or a foundation) in retaining walls or for ornamentation. Landscape professionals generally say that foundation rocks are too “raw” to serve attractively in the landscape (a buried stone gathers no moss, after all). But you should feel proud to reuse rocks from your site. You save twice on transportation that way: once because you don’t have to haul off these boulders, and again because you don’t have to pay to haul new ones in.

Another option is that you and your four-wheel-drive vehicle can bring fieldstones or small boulders home to use as garden edging or accents. If you’re visiting public lands, beware of local regulations. National parks ask that you take only pictures and leave only footprints, but most government lands allow removal of resources such as rock for “personal” use. Just don’t drive off the road to gather them.

Occasionally boulders that have been blasted or dug up during road construction projects can be had for an informal fee offered to the work crew; otherwise, they’ll likely be hauled away to the landfill if not to your yard. These rocks may be scarred by contact with heavy equipment, but that adds character.

And last, consider the alternatives. If you don’t use stone for your hardscape of paths and patios, what will you use? Concrete? If you don’t use stone for retaining walls, what will you choose? Treated lumber or railroad ties? Every material has its environmental costs, and the cost of stone is perhaps less than that of the others.

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