Potting soil has a grimy secret

Potting soil has a grimy secret

  • Atmosphere

The soil frail to grow potted vegetation and salvage raised beds appears to be like ideal. However it hides some traumatic complications for the atmosphere and our health.

Published November 3, 2022

6 min read

Nearly every tomato plant, pansy, or succulent you’ve ever bought first sprouted in something called potting soil, a concoction that steadily comprises neither soil nor compost. As a substitute, all these baggage at the nearest nursery are dirt-less sterile blends of peculiar mosses, fibers, and minerals, ingredients that hide lung disease, water extinguish, and a whopping carbon footprint.

So why use it at all? Ask for potting soil in america has exploded; the quantity of metropolis gardeners has risen 30 p.c within the final 30 years, and nurseries and greenhouses are the 2 fastest rising agricultural industries. Some lucky gardeners can grow straight within the ground, nonetheless dirt is simply too heavy and becomes too compacted for raised beds and seed trays.

That snappy rising query has increased the need for potting soil’s key ingredients: vermiculite, sphagnum peat moss, and coconut coir, all three of which would possibly possibly be volatile for environmental and human health, although bigger consciousness of these dangers is encouraging more sustainable alternatives.

“Increasing vegetation isn’t swiftly and simple,” says Linda Chalker-Scott, a professor at Washington Articulate University who writes the blog, Horticulturalist Myths. “If you establish to enjoy to enjoy a sustainable blueprint you’ve bought to enact it the correct formula.”

These are the tip three most problematic ingredients in potting soil.

1. Vermiculite

Valued in horticulture for its popcorn-admire texture, the mineral vermiculite is mined after which baked at over 1000 levels Fahrenheit into the sunshine crumbs we discover in potting soil. However the deep, open pits, heavy machinery, and propane-reliant manufacturing vegetation wreak havoc on the atmosphere, as can asbestos-immoral vermiculite on human health.

The best probably U.S. vermiculite mine, in Libby, Montana, become once immoral with asbestos. Shut down in 1990 as a consequence of of asbestos poisoning within the group after 70 years of sincere operation, Libby’s mine once produced 80 p.c of the realm’s vermiculite. Its distribution immoral a complete bunch of potting mixes, landscaping products, brake pads, chlorine filtration programs, popcorn ceilings, and the insulation of 35 million U.S. properties. Asbestos-immoral mines mild operate in Virginia, South Carolina, and South Africa.

Fortuitously, now not all vermiculite comprises asbestos. “The fact that we don’t discover more cases of mesothelioma in gardeners and farmers is a testament to the low percentage of contamination,” says Michelle Whitmer, an asbestos educated at The Mesothelioma Heart, “nonetheless repeat exposure, to even a low quantity, makes it unpleasant.”

Client safety laws are nonexistent for an excellent deal of horticultural provides bought in america. And a complete Environmental Protection Company ban on asbestos is mild within the proposal stage, 22 years after asbestos-containing vermiculite become once discovered in gardening and lawncare products from nearly 20 diversified retail manufacturers.

2. Peat

Made of spongy, waterlogged layers of slowly decomposing plant topic, peat is the predominant ingredient for the realm’s perfect potting mix manufacturers. Natural, noteworthy, sterile, lightweight, and nontoxic, it’s going to preserve 20 times its weight in water.

However peatlands are furthermore the realm’s perfect terrestrial storer of carbon, even greater than forests. Even though they duvet most productive 3 p.c of land and forests duvet 30 p.c, peatlands store twice as primary carbon.

Wetlands, by which peatlands are integrated, are already in decline—35 p.c since 1970. The most contemporary blueprint of harvesting peat can capture one thousand years’ payment of sphagnum peat moss within true one or twenty years. In North The US by myself, 3-5 million metric hundreds Canadian peat head south into the U.S. horticultural market every yr. That doesn’t embody the environmental footprint of processing, packaging, and transportation, says Justin Freiberg of the Yale Carbon Containment Lab.

In Europe, peat has been harvested for hundreds of years, largely for gasoline, nonetheless industrial peat harvesting is now banned in Ireland; the U.K. will ban all peat-based completely potting mix by 2024. Canada and the U.S. (where peat is mined in 11 diversified states) haven’t any bans.

3. Coconut Coir

As of late’s preferred substitute to peat is coconut coir, made of the fibrous shell left within the relief of after harvesting a coconut’s milk and meat. Pure coir is neutral, absorptive, and renewable. Valued as a fiber product for over a century, 90 p.c of the realm’s coir is despatched from Sri Lanka and India where, no topic a historical water disaster, it must be over and over soaked and rinsed one day of processing. As soon as the dehydrated coir bricks attain at their destination, they again require spacious portions of water for rehydration.

Previous water extinguish, the coir replace is wicked for low wages, child labor, and unpleasant work stipulations: A recent peep of Sri Lankan coir factories printed a payment of 1,063 accidents per 1,000 staff per yr.


We are entering into the “third paradigm of potting mix,” says soil scientist Charles Bethke, from heavy steam-sterilized garden soils to peat to the mannequin of “recycled lignose cellulosic fiber.” Which of these fibers is the most promising? Primarily essentially based on Brian Jackson, a professor and the most contemporary director of the North Carolina Articulate Horticultural Substrates Lab, “wood fiber and wood products are believed by every educated organization in Europe and North The US to be the very perfect-doable field topic to continue to salvage the void left within the relief of as peat is being frail less.”

However wood is now not the most simple likelihood. From corn stalks to peanut hulls, nettles to yucca, beach grass to recycled cardboard, there are an excellent deal of things that will furthermore be recycled into rising media. This vary of inputs furthermore makes it more uncomplicated to shift from long-distance transport to local manufacturing hubs.

Chalker-Scott encourages specializing in remediating the soil below our feet. “A hundred years within the past we didn’t enjoy potting mix,” she says. “Vegetation enjoy done true gorgeous without it.”