Even dirt isn't dirt-cheap anymore.

Even dirt isn't dirt-cheap anymore.

At your local garden center, the cheapest dirt, which often goes by the name of "premium topsoil," may cost $5 for a 40-pound bag, about a buck more than a year or two ago.

Then there's the gourmet dirt — the scientifically exquisite potting mixtures, soil enhancers and soil amendments, crafted from special ingredients such as peat moss, bark fines (partially composted pine bark), perlite, coconut husks, and/or "spent mushroom substrate." Some bags often go for $15, up two bucks from 18 months ago.

Dirt and its upmarket cousins offer a glimpse of how rising energy prices have caused inflation in the grittier corners of the consumer culture. Products that are cheap, heavy and bulky, such as bags of soil, are particularly vulnerable to rising freight costs.

Moreover, thanks to technology, globalization and changes in consumer preference, a bag of potting mix is now a highly manufactured, meticulously designed product, often containing ingredients from all over the continent and from across the planet.

Pricier dirt is what consumers want, says Bob LaGasse, executive director of the Manassas, Va.-based Mulch and Soil Council, which represents soil and mulch producers nationwide. "People have less time. So their garden projects have changed over time. Convenience, time-saving factors, less mess," he said. They want high-performance dirt, charged with organic nutrients.

"It's potting soil on steroids," said Chris Sexton, marketing manager for Fafard Inc., a major soil manufacturer in Anderson, S.C.

He said that an eight-quart bag of Fafard's premium potting mix would have retailed for less than $3 a couple of years ago, but now is likely to cost $4.

"Our input costs are just going up so much," Sexton said. "The peat moss comes from Canada. It doesn't come here magically. It has to come by truck or on the train."

What's in this stuff?

The purveyors of the more elaborate "growing media," it should be noted, never call it dirt or soil or anything so crass.

"We usually call it artificial growth substrate. It doesn't contain any mineral soil in general now," said Kathryn Louis, a technical specialist with Sun Gro Horticulture in Bellevue, Wash.

What does it have? Depends on the recipe, but any kind of topsoil or potting mix is likely to be crammed with composted organic material. Topsoils can be made from composted shellfish shells, for example. Potting mixes often contain sphagnum peat moss from bogs in Canada or Ireland. Bark fines might come from a sawmill in the Deep South. Coconut "coir," a peat moss substitute, gets shipped all the way from Asia.

A common ingredient in potting mixes is perlite, which makes the soils airier while also retaining moisture. In its final form, small white pellets, it appears to be something synthesized in a factory. In fact, it comes from a volcanic sand mined on the Greek island of Milos. Shipped to the United States, the ore is heated to 1,400 degrees Fahrenheit, at which point it pops into kernels.

Different companies have different recipes, with some variation depending on local materials.

"Just like making a cake. One hopper has peat moss in it, one hopper has perlite, one hopper has bark, several hoppers have fertilizer and limestone," said Steve Jarahian, who until his recent retirement spent more than 30 years concocting potting soil for Fafard in Anderson, S.C.

Dirt has been steadily evolving into "growing media" since the 1960s. Back then, a commercial greenhouse operator might simply have used topsoil.

But then the "soil-less" mixtures came along, often known as the Cornell Mixes, after the professors who developed them. They relied heavily on peat moss and either vermiculite or perlite.

Recently, environmental concerns have arisen about the use of sphagnum peat moss, which is "vacuum-harvested" from bogs in Canada. Paul Short, president of the Canadian Sphagnum Peat Moss Association, said that, after being harvested, the bogs are restored to functioning ecosystems: "Our view is we are a renewable resource," he said. Nonetheless, some consumers and companies are switching to coconut coir.

Steve Titko, a director of research and development for Scotts Miracle-Gro, said the industry has tried in recent years to shorten the supply lines and use more local, recycled materials in topsoils and potting mixtures.

The rise in the price of dirt reveals how intricately connected the various elements of the consumer economy are. A spike in costs in one sector can have reverberations across the board and into your backyard.

Potting mixes often contain chemical fertilizers. The price for fertilizer has risen sharply, in part because fertilizer requires a great deal of energy to manufacture and transport, and in part because demand has spiked. With corn selling for $7 a bushel — prices driven by the government-mandated and subsidized boom in corn-based ethanol — farmers are planting more crops and demanding more fertilizer.

It may be a sign of the times that even a dirt bag is getting expensive. The typical dirt bag is made of plastic, which comes from oil. Then there's the cost of the shrink-wrap that surrounds the dirt bags on the wooden pallets. And the pallets cost more because wood costs more. Why does wood cost more? Possibly because, with oil, coal and gas prices so high, wood suddenly is more attractive as a fuel source.

"Your plastic bag is, you know, up 10 or 12 cents over what it was last year at this time. Your stretch wrap — when you see a whole pallet, it's wrapped with plastic — that's affected. The pallet costs more — wood's up," Jarahian said. "Everything is related to oil."