Peat moss is a dark, spongy material made from partially decomposed plants that forms in waterlogged areas called bogs. When plants die in these wet, oxygen-poor environments, they don't fully rot away like leaves on a forest floor. Instead, they accumulate over hundreds or thousands of years, forming thick layers of peat.

Gardeners prize peat moss because it holds water like a sponge while keeping soil loose and airy. When you buy potting soil at a garden center, it often contains peat moss to help plants grow strong roots. The moss helps retain moisture so you don't have to water as frequently, which is especially helpful for seedlings that need consistent dampness.

Most peat moss comes from Canada and northern Europe, where vast peatlands have built up over millennia. These bogs are ancient ecosystems that store enormous amounts of carbon. When dried out, peat can even be burned as fuel, which people in Ireland and Scotland have done for centuries to heat their homes.