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What’s in the potting soil that you are using?

Chances are, if you are like most gardeners, you don’t really know. It’s dark brown, it’s moist and it looks like, well... potting soil. But, if you’re concerned about sustainability, global climate change and the environment, you might want to take a closer look in that bag.


The majority of potting soils, contain peat moss as their primary ingredient and that’s where the issues begin for a lot of environmentalists and a growing cadre of concerned gardeners.

If you’ve been a gardener for long, you are likely familiar with peat moss, but may not know about its associated environmental issues. Peat moss is the decaying plant matter that forms under sphagnum moss. As sphagnum moss grows, it layers upon itself, collecting and compacting dead matter beneath the living layer. Very slowly, the peat layer builds as more moss grows overtop, creating the rich, earthy, substance known as peat moss. Although devoid of nutrition or healthy biological microorganisms, it is a popular ingredient in most potting soils and some soil amendments.

What are the issues and why go peat free?

First, peat renews at a very, very slow rate. Since it is organic matter, many people assume that peat is a renewable resource. Technically, it is, since the moss is a life form that continues to grow. The problem is that it grows at a very, very slow rate - only 1 to 2 millimeters a year. This has lead to many debates about the renewable aspects of peat harvesting. A thousand years of peat growth is easily harvested in a week. Adding to the problem is the location of this peat resource.


Sphagnum moss only grows in northern bogs or wetlands. About 90% of the peat that is used in North America comes from commercially mined Canadian peat bogs. Peat sustains many Canadian wetlands due to its water absorbency (the same reason soil companies use it in their potting mixes) and when mass harvested, this ecosystem is eliminated.

The mining process involves digging a network of ditches and basins around and through the bog, then draining the water away from the wetland, causing the area to dry out and die. Once that happens, the surface plants are removed and the peat harvesting begins.

The second big concern is that peat bogs store carbon, lots of carbon; and that’s a big issue among global warming scientists. Although they cover only 3% of the world’s land area, peatlands contain almost 30% of all the carbon stored on the earth’s lands. Of course, the release of carbon into our atmosphere is the primary cause of global warming. The more peat we harvest, the more carbon we put into our atmosphere and the more global warming.

How exactly does peat moss fight global warming? Well, as the mosses grow, they absorb carbon dioxide, which becomes locked up within the plants structure and remains there as the plants decay and turn to peat. Scientists think that peat bogs contain more carbon than all the world’s tropical rainforests combined. Each square yard of a peat bog may contain several hundred pounds of undecomposed organic matter, for a total of between 200 and 450 billion tons of carbon stored away in peat bogs worldwide. But when the bogs are disturbed or drained for peat extraction, the peat starts to decompose and the carbon dioxide is released back into the atmosphere, where it acts as a potent greenhouse gas, trapping heat; much like the burning of fossil fuels.

Third, peat bogs are home to a large array of flora and fauna that thrive in these unique environments.

Although a small amount of peat is used as fuel in Europe, in the U.S., peat moss is almost exclusively used in horticulture. 40,000 acres of peat moss are currently being harvested in Canada, with 90% of the product destined for the gardening industry. Many conservationists, gardeners, and wetlands scientists are now recommending a boycott of peat. England’s famous Royal Horticultural Society has targeted a  90% reduction of its own peat use by the end of this year and the England’s government has set aggressive targets toward a huge reduction in peat consumption. England’s largest retailers of peat moss, companies similar to our own Home Depot and Lowe’s, have agreed to meet or exceed these targets. Bravo!

Yet in the U.S. the peat moss debate has barely reached a whisper. If I’ve piqued your interest, I encourage you to do a little more research and then make your own decisions about your consumption of peat moss.

Next time you’re picking up one of those potting soil bags, flip it over and take a look at the ingredients. It might be worth knowing what’s in the bag.

Ron Vanderhoff is the Nursery Manager at Roger’s Gardens, Corona del Mar.

Questions from Readers August 8.

Did you notice that the Costa Mesa Sanitary District is offering residents Earth Machine compost bins for only $20.  I looked it up and found it selling for $100. I picked up one today and it seems sturdy and well designed. They seem to have a good supply and have more on order. Your readers might want to know about this.  Information is available at www.cmsdca.gov or by calling the Costa Mesa Sanitary District office at (949) 645-8400.

Van Wright, Costa Mesa


Thanks for the tip Van and good timing, considering the topic of this week’s column.


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