Peat moss is the decomposing, dead parts of sphagnum moss that usually are found deep in a bog. It is rich in organic matter, and typically can hold up to 20 times its weight in water. For this reason, peat moss mulch can be used in dry areas to help retain water. It also is acidic and can be used to lower the pH in soil. Growers of carnivorous plants typically use peat moss because those plants usually need a wet environment to flourish.

Grown in bogs around the world, peat moss is deposited at a rate of about .05 inches (about 1 mm) per year. This means that a 3-foot (about 92 cm) deep patch would take around 750 years to grow. Extensive harvest of peat moss is unsustainable due to its slow growth. New Zealand has taken strict measures to make sure that its peat bogs are not over harvested. Peat bogs store high amounts of carbon, so their preservation can be critical for helping to curb greenhouse gases.

Peat moss has myriad uses. Adding it to a lawn can promote healthy root growth, usually a necessity for a lush lawn. If a garden needs a soil conditioner, a 1-inch (about 2.5 cm) layer mixed into soil could do the trick. It is not recommended to use peat moss as a yearly mulch. This can make soil extremely acidic, a problem that can be difficult to repair.

Compost piles can benefit from the addition of peat moss soil. It usually is recommended that for very 4 inches (about 10.2 cm) of compostable material, 1 inch (about 2.5 cm) of peat moss soil should be added. Compost typically relies on water and air to have good microbial action, and peat moss helps in this process. Sprinkling lime or wood ash on top of the layer of moss can help balance acidity. A low pH usually will prevent a compost pile from being active.

When transplanting young plants, 1 inch (about 2.5 cm) of peat moss can be placed at the bottom of the new hole. It usually is not necessary to temper this layer with lime unless the plant is susceptible to a low pH, or the area is frequently used for new plants. Peat moss takes years to decompose so a layer can be a long-term source of nutrients for fledgling shrubs or bushes. Using peat moss sparingly in a garden usually means healthy root growth in compacted soil and excellent water retention in arid areas.