Unopened bags of potting soil lasts for about 2 years when stored properly. If the bags are opened and exposed to air, the potting soil should last for 6 months before it starts to lose its nutritional benefits. The shelf life depends on what kind of soil you are buying. For example, peat-based soils have a longer shelf life than other kinds of soil. Peat-based soils tend to stay fresh for 3–5 years. However, they need to be kept cool and protected from direct sunlight. Once opened, store them in an airtight container.