Peat moss is a soil amendment that is a dark-brown fibrous material used as a planting medium for growing plants. Plants that like peat moss are usually acid-loving, such as azaleas or blueberries, for example. Container-grown plants also like the material because it helps retain needed moisture in the soil. Peat moss is naturally made or formed after 1,000 years and harvested from peat bogs. There's much debate about its environmental safety since it's not sustainable and gives off carbon dioxide when harvested.
Peat moss is soilless but is often added to soil to lighten, aerate, and help retain moisture. Although peat moss is good for keeping in moisture and aerating the soil, peat moss is not often used for lawns since its acidity hinders grass growth and can kill earthworms.
The most significant disadvantages of peat moss are that it's too acidic for non-acid-loving plants, it's not renewable, and it doesn't have any nutrients. The upside to peat moss is it's sterile and free of weed seeds; however, weeds can still grow in peat moss once you start using it and it's exposed to the elements. Also, once you start using it, peat moss can attract bugs like fungus gnats since it's also decaying.
Find out more about peat moss, what it is, how it compares to other materials, how it's used, its benefits, and its potential downsides.
What Is Peat Moss?
Peat moss comes from peat bogs, many of which are found in the wetland areas of Canada. Peat bogs are formed, over the course of very long periods of time, as organic materials partially decompose. Because of the water in these bogs, anaerobic conditions are maintained. Anaerobic conditions slow down full decomposition. The result is that the peat moss is preserved almost indefinitely. Peat moss is made from these layers of decomposing organic materials, one of which is once-living sphagnum moss.
Though you technically can't make your own true peat moss, you can replicate it by making leaf mold, which is also a soil amendment made from composted leaves. Peat moss is commonly sold in bales (covered in plastic) at home improvement centers. When you break open a bag, the substance resembles very dry, caked-up soil.
Peat Moss vs. Sphagnum Moss
"Peat moss" and "sphagnum moss" are closely related, but the two terms are not synonymous. Here is how the two differ:
First, "sphagnum moss" refers to a living plant. There are 120 species of this type of moss plant. Sphagnum moss is native to many countries across the globe, but it is especially prevalent in the Northern Hemisphere. "Peat moss" is not alive; it's long dead.
Like peat moss, sphagnum moss is harvested for the horticultural trade. For example, it is commonly used to line wire baskets for hanging plants to retain the soil. But the sphagnum moss used for this purpose was a plant growing in nature not long ago. You can also tell from its appearance that it is a type of moss, whereas peat moss bears more resemblance to soil.
How Peat Moss Is Used
Peat moss is used in soilless potting mixes. So if you have started plants indoors from seed, you have likely already dealt with peat moss. A soilless potting mix is much better to use for starting seeds than regular soil for the following reasons:
- Regular soil is too heavy for plants, just sprouting from seed. The tender, young roots have trouble pushing through it.
- Drainage is also generally poorer in regular soil, and seeds may rot in it before they ever get a chance to sprout.
- Regular soil can also harbor pathogens that could quickly kill young plants.
But peat moss has other uses, as well. Outdoors, it can be tilled into a planting bed where the soil is not sufficiently friable. Peat moss will lighten up the soil in your garden, which may have become compacted over the years, resulting in inadequate drainage.
An ideal soil will retain enough moisture to keep your plants irrigated. But you do not want all of the water to pass quickly through your soil. It is a delicate balance, and peat moss mixed in with soil (you can't just put peat moss on top of soil or it could harden or blow away), with its ability to retain water, will help you achieve that balance.
Benefits of Peat Moss
The popularity of peat moss as a soil amendment can be accounted for by listing the following pros:
- Lightweight (which helps you as well as your plants, because pots filled with such soilless mixes are easier to transport)
- It promotes sufficient drainage and doesn't get as compacted as soil
- Retains just the right amount of water
- Sold to the public after being sterilized to remove pathogens; doesn't have bacteria, fungus, harmful chemicals, or weed seeds
- Readily available; easy to find at nurseries and garden shops
Disadvantages of Peat Moss
Peat moss comes with some cons:
- It doesn't add any nutrients to the soil.
- It takes hundreds of years for peat moss to be created in nature. It is not considered sustainable.
- Peat moss is acidic. So while it is an ideal soil amendment for acid-loving plants, you may have to add garden lime to your planting bed to raise its soil pH over time if you are growing plants that want a higher pH.
- It holds water well, but if you allow it to dry out, it can take a while before it reabsorbs water.
- It's not free. Although it's not expensive, if you need a lot of it, you will have to pay for it.
Peat Moss Alternatives
Peat moss is a great planting medium, but its drawbacks are sufficient for some people to look for viable alternatives. Consider these peat moss alternatives:
- Coconut coir: Coir is a by-product of coconut fiber and is a renewable, more sustainable option. Coir is increasingly used as an alternative to peat moss in soilless potting mixes. It has a neutral pH, retains water, and provides better soil aeration than peat moss, but it is more expensive.
- Compost: It is made from decayed organic materials like rotted plants, leaves, vegetable scraps, and animal manure. It holds water well and is rich in nutrients.
- Bark or wood fiber: Bark chips and wood by-products like sawdust make potential alternatives to peat moss. They add organic matter, aid water retention, help aerate, and are a good use of waste materials.
What is the difference between peat and peat moss?
Although sometimes referred to as "peat" for short, peat moss and peat are not, technically, the same. "Peat" is the broader term: Peat moss is just one of the products harvested from peat bogs. Other kinds of peat come from the partial decomposition of other organic materials. The "moss" in "peat moss" refers specifically to sphagnum moss (for example, Sphagnum cymbifolium) that is one of the decaying organic materials in a peat bog.
How long does peat moss last?
A dry, closed package or bale of peat moss should not have a shelf life since it's decaying or dead matter. However, you may want to replenish peat moss in your soil after a few years as it may naturally wash away.
Is topsoil better than peat moss?
Peat moss isn't better or worse than soil; it's different. Peat moss is sometimes added to enhance the topsoil's environment for growing healthier plants.
Peatlands store twice as much carbon as all the world's forests. UN Environment Programme.