Peat moss – pH


What is the PH value of peat moss? Some people say Canadian sphagnum peat moss is very acidic with a PH of 4 while other peat moss is PH neutral or between 6 to 7. Are they true? Is Canadian sphagnum peat moss too acidic for vegetables when added to the bed? Thanks.


Sphagnum moss is a living plant that grows on soil surfaces.  When we buy sphagnum moss, it has been dried, and comes as either long-fiber or milled (chopped) moss.  It is used as a basket liner, or seed-starting medium and often as an amendment in potting soil.  It helps improve water retention and aeration in soil. The pH is generally neutral (i.e., around 7).

Peat moss, which is often called “sphagnum peat moss” starts out as sphagnum moss, but the moss dies and layers and layers build up on the spot over hundreds or thousands of years.  The layers of dead material form a bog, and the moss (which has become very compacted) is called peat moss.   Peat moss is very low in pH, generally 3 to 4.5.  It is used in potting soils and garden soils, and helps lower soil pH.   It also enhances soil aeration as well as the ability of soil to hold water, and helps prevent soil compaction.  The latter is important when soil is sandy or rocky and dries out quickly.  Note that it does not provide plants with nutrients.

As mentioned above, both sphagnum moss and sphagnum peat moss can help aerate the soil and enable the soil to hold water, so can minimize the impact of extreme conditions of soil dryness or sogginess.  If you plan to use sphagnum peat moss (low pH), I’d suggest checking the ideal pH for the vegetables you plan to grow – some vegetables may thrive in acidic conditions, others not so much (lime may be added to increase the pH).  Amending the soil with both peat moss and compost (which adds nutrients) is often recommended.

Peat bogs are not renewable resources and destroying them contributes to climate change.  You may see recommendations to decrease the use of peat in gardens, and may wish to explore this issue further.  Canada is a huge supplier of sphagnum peat moss, and the Canadian Sphagnum Peat Moss Association promotes the sustainable manage of peatlands.   Coconut coir or ground newspaper are among the alternatives for peat moss.