A powder made up of the dried up husks of a single celled algae (diatom) whose cell walls contained silica. Because of the crystalline structure of the silica it can be ground up and produce a seemingly talc like powder, but under closer inspection the powder is really a mass of sharp edges from the broken up shells of diatoms.
Diatoms make up a majority of marine plankton that float, en masse, in the oceans and lakes of the world. Since diatomaceous earth is found in dried up lake beds and dried up sea beds it’s availablity is world wide. Though the uses of diatomaceous earth are many, the one use that is on the minds of gardeners is pest control.
The broken up shells of these small creatures have proven to be a very effective mechanical means of insect control. The sharp edges cut and tear the exoskeletons of garden insects leaving open wounds that cause the insect to lose moisture and succumb to dehydration. Ingestion of diatomaceous earth will cause great internal injury, to insects, due to the microscopic sharp edges leaving you with the desired results of dead pest insects. Food grade diatomaceous earth is safe for human or animal ingestion it’s often used as a dewormer in both species. Though precautions need to be taken not to breath in the dust, wear appropiate saftey equipment (face mask) when handling diatomaceous earth.
Diatomaceous earth is rather indiscriminant it will kill beneficial insects as well as the pest insects so using a little discretion when using the powder will get rid of the pests while saving beneficial insects. Instead of dusting the whole garden, use the powder in strategic locations, like surrounding certain vulnerable plants or only dusting the plants where you see infestation.
Diatomaceous earth is also used as a potting medium like vermiculite or perlite, it retains nutrients while draining water quickly – what better way to start your plants than in a medium that is sterile but deadly to garden pests.