What is Peat Moss?

Peat moss is the dried and decayed form of Sphagnum moss. Peat moss is rarely used alone as a plant growth medium, more often it is mixed with soil to increase the soil’s ability to retain moisture and nutrients, and regulate the air around the roots. Soil amended with peat moss is able to retain moisture steadily and is especially helpful for improving heavy sandy or clay soils. 

Since the soil mixed with peat retains more moisture, leaching and runoff of nutrients are reduced. Sphagnum moss plants are able to hold 16-20 times their dry weight in water depending on the specific moss species. Peat moss may acidify surrounding areas due to its ability to take up minerals like calcium and magnesium, and release hydrogen ions. The ability to lower soil pH is especially beneficial in balancing alkaline soils.

Peat moss has a pH of 3.0-4.5, high amounts of humus (organic matter), high porosity for moisture penetration, and low density for moisture retention. Peat moss has a cation exchange capacity of 80-180 mg/l (similar to that of loamy soil) which is an indicator of low to moderate fertility and ability to retain nutrients. A volume of 65-210 kg/cm3 peat moss studied had 87-95% pore space, 69-83% water volume, 6-26% air volume.

What is Peat Moss?

The horticultural use of peat moss as a soil conditioner started around the 1960s and gained popularity after 19704. In addition, to use as a soil conditioner, peat moss is used to make peat pellets and peat pots for germinating seeds and starting plants, When plantlets are ready to be transplanted, both peat pellets and pots may be planted directly into the soil and dissolve with time. Prior to that, and still today, peat has been mainly used in a brick form to burn for home heating. The use of peat for heating goes back hundreds of years and is attributed as the main cause for the depletion of peat from bogs in the UK.

Uses of Peat Moss

  • Enhances moisture retention when blended with potting soil
  • Growth medium for carnivorous plants and orchids
  • Vital for the casing process when growing mushrooms
  • Liner for hanging baskets
  • Peat pellets and peat pots
  • Soilless planting mediums

Mixing and Using Peat Moss

If you choose to add peat moss to your flower bed or garden before planting, you can plan how much you will need by figuring that 180 square feet of 1-inch deep peat moss coverage can be had with a 3.8 cubic foot bale of peat moss. Compost may be raked in with the peat moss and it is a good idea to test the pH of the soil after amending it. Lime can be added to increase the pH of the soil if the peat acidifies it too much.

Soilless peat-based mixtures generally also incorporate perlite, vermiculite, and added nutrients. Peat is almost completely void of nutrients naturally, so they must be added if they have not already been mixed in with the retail product. Since it is almost impossible to re-wet peat, a wetting agent is also usually added to these mixtures. Peat breaks down quickly and should not be used as a mulch. Peat should also not be added to compost bins. While small amounts will not do much harm, large amounts could have very negative impacts on pH and moisture, and alter the natural decomposition process.

Adding peat to soil should be done with some caution. It is very dusty to work with and may cause lung irritation. A respirator should be worn, and if adding to garden soil, it is suggested to do so on a day that is not windy.

Fun Facts: History and Environmental Impacts of Peat Moss

Peat found in undisturbed peat bogs can be hundreds of years old. Because peat created a unique anaerobic environment in the bog materials, and even deceased organisms, that are submerged can be preserved for hundreds of years. Harvesting peat disturbs this environment, but it has been claimed that the ecosystem rebalances itself within 5-20 years. One inch of peat can form in a bog over 15-20 years. 

Of more concern is the fact that peat sequesters a large amount of carbon dioxide. Peat mosses are one of the most important plant species when it comes to balancing the planet’s CO2 levels to combat global warming. Thanks to peat moss, 550 billion tons of carbon are sequestered in the world’s bogs, which is around 10% of the world’s CO21. When it is harvested, CO2 may be released and the ecosystem’s ability to sequester more of it is reduced. 

While some feel horticultural use of peat is of minor environmental impact, and that restoration programs successfully prevent depletion and allow habitats to re-establish, others feel that the use of peat is unjustified due to its environmental impacts. When peat is mined, the top layer of the living sphagnum moss is scraped off which disturbs the habitat of other plants and animals, some of which are endangered dragonflies, frogs, and birds. The bogs may be restored with time, but there is no avoiding the immediate environmental impacts. The peat bogs play an additional role in preventing flooding which can become a local problem if the bog if harvested.

90% of mined peat comes from Canada and is sent to the US for horticultural use which consumes around 40,000 acres of peat moss. While it represents a very small portion of global peat bogs, some fear it will eventually result in depletion such as in the UK where 94% of bogs have been altered or destroyed. 

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