Tuesday, August 3, 2021

Peat moss is never sustainable

There are many reasons why peat moss is never recommended for gardening.

Soil sequesters carbon

Before we get to peat moss, let's look at soil in general. Soil is made up of organic and inorganic components, but all the carbon is found in the organic matter, which is made up of carbon-rich plant and animal matter. The carbon stored there all depends on photosynthesis where carbon dioxide and water are turned into sugars that were used to sustain life for all terrestrial organisms in one way or another. While forests are often credited for sequestering the majority of the carbon in those areas, the soil retains four times more carbon than all the terrestrial plants, including rainforests, on a world-wide basis. Forests are tremendously important for many reasons and they do temporarily sequester carbon. I explain all this in, "Transpiration: Forests' most important service."

Of all the soils around the world, peat makes up only 3% of the total acreage, but it sequesters 21% of the sequestered carbon, so peat left in place in the ground plays a tremendously important role in keeping our planet cool.

What is peat?

Peat, partially decomposed organic matter (dead plants, animals, and their waste), is formed in soil when there is little or no oxygen present—a condition called hypoxia. In regular soil, organic materials decompose relatively quickly, but with peat, since there is a lack of oxygen, it’s missing the soil microbes and other organisms that would normally digest the organic matter. Peat forms slowly and may build up for thousands of years, which means that peat sequesters carbon on a long-term basis.

Peat is formed in several types of ecosystems. The most well-known are the peat bogs of the north in North America and Eurasia, but hypoxic conditions where peat forms can also be found in saltmarshes, mangrove forests, some areas of rain forests, and pine barrens.

Saltmarshes are subjected to a twice-daily flooding and draining cycle and are populated mostly by certain grasses that can withstand both the salt and the flooding. Because of the frequent wash of saltwater, there’s little or no oxygen in the soil and the plants generate and capture organic materials and sediment which builds up over time. It’s peat, but it’s different than peat from bogs because of the sediments. While some carbon escapes as gases--carbon dioxide and methane, mostly, the saltmarsh peat keeps the carbon tied up or sequestered for the long run under the top saltmarsh living layer. And because of the tidal flows with their sediments, the level of the salt marsh rises along with the sea levels--about five inches a year in some places.

The mangroves are another type of wetland of the coastal ecosystems, and are located in most tropical and subtropical areas. Much like the saltmarshes, the accumulation of leaves, sediments, animal waste and dead animals creates a detritus on the surface that becomes incorporated into the soils and depending upon their location and local currents, this allows mangroves to keep pace with rising sea levels--mangrove soils can grow vertically at rates of up to 5 inches per year.

Some mangroves sit on top of deep layers of mangrove peat, some that have been analyzed, have built up over thousands of years. Because of how they live and reproduce, mangroves can sequester carbon for much longer than other forests.

Pine barrens
Pine barrens, pine plains, sand plains, or pinelands occur throughout North America and parts of Eurasia. They occur on dry, acidic, infertile soils and are dominated by grasses, low shrubs, and small to medium-sized trees, mostly pines. Maybe the most well-known are the pine barrens in New Jersey. The trees are stunted in size because of the extreme acidity. I've seen red maples (Acer rubrum) in the NJ pines barrens that have tiny leaves that are about the size of a quarter instead of their normal three- to four-inch leaves.

Most rainforests have only a thin layer of topsoil because of the high temperatures and the high rainfall, but some areas of both tropical and temperate rainforests sit on top of deep peat, and in fact, a huge peat deposit the size of NY State was just found in the Congo rainforest in 2017.

Peat bogs
Over hundreds of thousands years, repeated glaciation in the Northern Hemisphere sheared off mountains and eroded steep slopes, creating shallow basins, plains and flat-bottomed valleys. These features provide perfect conditions for wetlands and peat formation. Most bogs began as ponds or small lakes called kettle holes that are lined with impermeable materials like solid rock or clay. Because the bog receive no minerals or other nutrients from the rain and snow, they are nutrient poor. These soils are called ombrotrophic or cloud-fed. And because of the lack of minerals and the dominance of the sphagnum moss, the bogs become extremely acidic.

These kettle holes, became filled with water and plants that can survive the low nutrient environment. The vast majority filled sphagnum moss that begins to grow at the edges and then expands out into the water, eventually covering the water and then expanding out from the original kettle hole boundaries and the acidification and added water kills off the surrounding trees in a forest. But this is a SLOW process the peat is formed at a rate of about one mm per year. Unlike peats in salt marshes and mangroves, there are no sediments added because all the water comes from the sky.

Sphagnum moss, the main plant in bogs
There are more than 300 different species of this plant (Sphagnum spp.) but the differences between them are so small that you'd need a microscope to determine the species. Sphagnums are a true mosses-- non-vascular, non-flowering plants that reproduce with abundant spores that are carried great distances in the wind. So any time a new wet area is exposed, the moss spores are there to begin a new population.

There are many leaves along the stems. The leaves consist of two types of cells: small, green living cells (chlorophyllous cells) and large clear, structural dead cells (hyaline cells) that have a high water holding capacity. Hyaline cells not only help sphagnum moss tolerate drier conditions by storing water, but also contribute to its large water holding capacity after it’s dead. Sphagnum moss may hold 16 to 26 times as much water as its dry weight depending upon the species and location. Because there are no vascular cells (xylem and phloem) to carry water and nutrients high into the plant, it stays low and close to the water.

Peat bogs are nutrient poor

When you look at peat moss, it looks like good rich soil, but its acidity prevents plants from absorbing nutrients. So most plants can’t survive in these bogs, and indeed, natural peat bogs are so acidic that they have a very low diversity of plants.

The very low diversity of plants in peat bogs is an indication that peat does not offer enough nutrients.

Even though plants don’t have brains, some have figured out how to get things done. Hence, the evolution of various types of carnivorous plants that can survive in peat bogs because they absorb nutrients from their prey and with so little competition from other plants, they have carved out a specialized niche in this tough ecosystem.

Three groups of carnivorous plants have evolved to gain enough nutrition 
to survive in nutrient-poor soils by catching bugs and other small animals.

Peat harvesting

Because of its abundance in northern Eurasia, early peoples relied on it for many uses, especially burning it as fuel since trees in this region are relatively rare. This has continued for centuries, but once a peat bog has been harvested, vegetation and hydrology changes. The harvested area is no longer a bog and all the carbon that had been sequestered for thousands of years is released into the atmosphere as the peat is exposed to the oxygen and dries out.

Today, the peat harvesting continues both in Eurasia and in Canada. Whether by hand cutting or machine vacuumed, the peat harvesting rate is far greater than the deposition rate which is One (1) mm/year.

Peat develops in its oxygen-poor environment at a very slow rate--about 1mm per year.
It can never be a sustainable product.

Peat moss in the garden

For many years, peat moss has been widely used in gardening both as a sterile soil amendment to increase the retention of moisture and molded into peat pots and liners for hanging gardens. 

Here are the advantages:
- It’s sterile so seedlings are less likely to be attacked by fungal wilts
- It's highly absorbent.

Disadvantages for peat moss in the garden are:
- It's extremely acidic and offers almost no nutrition available for plants.
- Once it dries out, it’s very hard to wet (hydrophobic), which will require much more work and more water to prevent plants, especially young seedlings, from wilting. 
- Its acidity kills soil microbes--it's antiseptic. In order to have a garden with healthy plants, the soil ecosystem filled with microbes and macrobes needs to be functioning so it can support the plants where it counts—around their roots. There are complex exchanges of favors between the roots and the microbes.
As citizens of our only planet, we are 
responsible for her care. Not using peat moss
is a small sacrifice for the greater good.

- The most important disadvantage is that Peat moss NOT a renewable resource and can never be harvested sustainably. So as it’s mined all that stored carbon will be released into the atmosphere and the peat ecosystems cannot recover fast enough to start absorbing carbon with enough volume to offset the loss. 

Some peat-harvesting organizations claim that their efforts to restore the peat ecosystems after mining, mean that their operations are sustainable. These claims are not true, because no matter what they do for restoration, it can never make up for the release of all that sequestered carbon from those peat bogs.

Alternatives for peat moss

There are alternatives such as:
- Coconut coir (pronounced core) made from coconut husks, a waste product from something that’s already been grown, harvested and used for its nut or milk. Coir is neutral, not acidic, and offers the same water retention as peat, but its nutrients are available to plants.
- Compost is also a better and highly renewable product that you can make from your garden waste. I've written several articles on composting with links available on the Green Resources Page on this blog.

Most gardeners I know want to take good care of their plants AND our planet. And this is why the name of this blog is Green Gardening Matters, because it does matter and we, the millions of gardeners, can and do make a real and significant difference. Not using peat moss is just a small sacrifice in our mission of greener gardening.

Green Gardening Matters,
Ginny Stibolt


-  Peatland Acidification and Understanding pH

- The underappreciated potential of peatlands in global climate change mitigation strategies

Transpiration: Forests' most important service

Dealing with hydrophobic soils

The Rhizosphere - Roots, Soil and Everything In Between

- Links to composting articles are on the Green Resources Page


  1. Thanks for the deep dig into peat moss. I have a better understanding. Carole

  2. Have you worked with PITTMOSS yet? www.pittmoss.com

  3. Thanks for the information on a more sustainable product.