A healthy soil is better able to infiltrate and retain water. A healthy soil with plenty of soil life, such as roots, worms and microorganisms is looser and better aerated. Adding organic material or planting the soil will stimulate soil life. Materials that can be used include compost, grass clippings, wood chips, cocoa shells, humus-rich soil and manure. More expensive improvers are bentonite, biochar and lava rock. Of course, the quality of the soil must be carefully considered when choosing improvers.