Potting soil serves as the home for container-bound plants. It provides nutrients, holds water and protects plant roots from excessive temperature changes. The prevailing thinking is that gardeners should replace all container soils every year. Full replacement of container soils creates a big expense. Budget-conscious gardeners do have options to conserve soil and save money. It requires a lot of effort and time to properly recycle potting soil. Weigh the effort against the benefit to determine if it's right choice for your container garden.
Remove all foliage and roots from the potting mix. Sift through the mix to check for buried pieces of roots. Discard any potting soil that contained diseased, dying or infected plants during the previous growing season.
Pour loose potting soil into one plastic tub. Continue adding sifted soil until all potential planters have been emptied into this larger container. Consider this soil "dirty" and do not mix new or purified potting soil in this container in the future.
Set the oven temperature to 200 degrees F. Pour a layer of potting soil into a large aluminum pan and spread evenly across the surface, as recommended by Colorado State University Cooperative Extension. Don't mound the soil in the middle of the pan or extend the soil above the edge of the pan.
Place the potting soil mixture into the oven for 2 hours on the lowest rack. Carefully remove the pan from the oven with potholders after the allotted time and allow it to cool for an hour. Dump the entire contents into the wheelbarrow or onto a tarp, advises The Oregonian newspaper online. Continue cooking and dumping all the potting soil to permit easy addition of amendments to a large volume of sterile potting soil.
Add peat moss or perlite, in total quantity equal to about a quarter of the volume of sterilized soil and mix completely, advises The Oregonian. Peat moss boosts the soil's organic content and perlite improves moisture retention.
Perform a soil test on the reworked potting soil. The pH level will probably be lower than the preferred level of 6.8. Add lime to the mixture based on recommendations on the product packaging.
Add 1/2 to 1 cup of granulated fertilizer or commercial compost to the mixture and distribute evenly. Transfer the entire mixture to a clean storage tub for use in future container gardens. Store in a covered container or in a sheltered location.