A soil conditioner is a product which is added to soil to improve the soil’s physical qualities, usually its fertility (ability to provide nutrition for plants) and sometimes its mechanics. In general usage, the term "soil conditioner" is often thought of as a subset of the category soil amendments (or soil improvement, soil condition), which more often is understood to include a wide range of fertilizers and non-organic materials.
Soil conditioners can be used to improve poor soils, or to rebuild soils which have been damaged by improper soil management. They can make poor soils more usable, and can be used to maintain soils in peak condition.
A wide variety of materials have been described as soil conditioners due to their ability to improve soil quality. Some examples include biochar, bone meal, blood meal, coffee grounds, compost, compost tea, coir, manure, straw, peat, sphagnum moss, vermiculite, sulfur, lime, hydroabsorbant polymers, and biosolids.
Many soil conditioners come in the form of certified organic products, for people concerned with maintaining organic crops or organic gardens. Soil conditioners of almost every description are readily available from online stores or local nurseries as well as garden supply stores.
Polyacrylamides were introduced as "linear soil conditioner" in the 1950s by Monsanto Company under the trade name Krilium. The soil conditioning technology was presented at a symposium on "Improvement of Soil Structure" held in Philadelphia, Pennsylvania on December 29, 1951. The technology was strongly documented and was published in the June 1952 issue of the journal Soil Science, volume 73, June 1952 that was dedicated to polymeric soil conditioners. The original formulation of polyacrylamide soil conditioners was difficult to use because it contained calcium which cross-linked the linear polymer under field conditions. Krilium was abandoned by Monsanto.