Soil amendments are added to existing topsoil to increase the organic matter and humus content of soil. This acts as a natural fertilizer that promotes healthy soil ecology.
Compost is organic matter that has been decomposed into humus. Compost is very rich in nutrients and is a very effective fertilizer. Compost also improves moisture retention, reduces soil compaction, and moderates soil temperature. Compost is well composted and does not have an offensive odor, meaning it can be readily applied in residential contexts.
Mushroom soil, or Spent Mushroom Substrate, is the steam pasteurized, partially composted remains of mushroom growing media after a crop of mushrooms has been harvested. While this product has some smell, it can be further composted into an odorless compost in 6 to 12 months. It can also be used directly as a mulch for vegetable gardens or flower beds. Do not use mushroom soil around woody shrubs that prefer acidic soil.