How to Use Soil Amendments-Sphagnum Peat Moss

By Grow Organic     30 August 2021 

Peat moss is an excellent soil amendment for your acid-loving plants. There are approximately 12,000 species of moss, but it’s only the 380 species of sphagnum moss that create peat. Bogs and fens form where sphagnum grows because both living and dead moss absorb and store water. As it grows, it spreads onto drier areas and turns those into bogs as well. Peat does not decay very easily in the bog conditions, due to the sphagnum cell structure and to slower-acting anaerobic conditions. Although it grows very slowly, it can accumulate to a depth of many meters. The live moss grows on top of the dead moss, and it is the dead moss that forms the peat we use in the garden.

Benefits of Adding Peat Moss to the Soil

  • Excellent for increasing water retention in your soil. It can hold up to 20 times its weight in water.
  • Good for holding onto nutrients in the soil.
  • Good source of organic matter, which will slowly degrade over a year or two to feed your soil.
  • Improves soil structure, promotes good drainage, and prevents compaction.
  • Good for adding to acid-loving plants since it has a pH of 3.5 to 4.5.
  • It is also naturally weed free.

Before Adding Peat Moss to the Soil

  • Measure your soil's pH. Before using peat moss, you should consider what you are growing and what your soil’s pH is. Because it is so acidic, it should only be used for acid-loving plants such as blueberries, or in soils that are naturally neutral or alkaline.
  • Pre-wet your peat moss. Before using peat moss, you will need to wet it thoroughly. Scoop out as much as you will need into a large bucket or wheelbarrow. Add water and stir, then let it soak for a few minutes. Add more water and stir as needed until it is completely soaked. It should be wet enough that when you squeeze a handful, a drop or two of water comes out. However, it should not be so wet that you can squeeze out a whole stream of water! Don’t skip this step, because dry peat moss will initially repel water. You must wet it for it to work like you want in your soil!

How to Use Peat Moss in the Garden

  • Apply peat moss in a 2–3 inch layer in your garden, and incorporate it into the top 12" of soil.
  • For containers and raised beds, use between 1/3 and 2/3 peat moss mixed with potting soil or compost.
  • To use for starting seeds, you can mix it 50/50 with perlite, or 1/3 each of peat moss, perlite and a soilless mix such as Quickroot. Sphaghum does not contain sufficient nutrients of its own so you will need to fertilize your starts regularly with a liquid, such as with Liquid Fish.

Sphagnum peat bogs are fragile ecosystems that are slow to regenerate after being harvested. It takes one thousand years for them to grow a yard in depth. Even though harvest is carefully regulated, peat moss is not considered a renewable resource or a sustainable product. There are numerous garden situations where it is the best choice: for blueberries and other acid lovers, for the specialized propagation method of air layering, and for mushroom production. But when it comes to growing everyday vegetables, seed starting, and improving the organic matter and water holding capacity in your soil, there are more environmentally friendly choices. Rice Hulls or Coco Peat can meet these same goals using repurposed plant-derived waste products. Compost and worm castings are just as good of a source of organic matter. Use sphagnum peat moss for your specialized gardening needs, and grow organic for life!