Diatoms are common single-celled algae found in the phytoplankton of both fresh and salt waters. They can also live inland under semi-aquatic conditions on wet soils, mosses, and bark. Microscopic in size; their common length is about the width of a human hair.
Similar to plants, diatoms rely on light and carbon dioxide for photosynthesis. They are an important contributor to both global carbon sequestration and oxygen generation. In the areas they inhabit, they are invariably an important part of the food chain as a source food.
Diatoms are distinctive for being surrounded by rigid “shells” known as frustules. These frustules are made from hydrated silica oxide and come in a variety of shapes dependent on the particular species of diatom. The shapes tend to be intricate and geometric, forming a protective silica cover dotted with openings for nutrient uptake and waste disposal. An organic coating helps prevent the silica from dissolving while the diatom is alive.
When an individual diatom dies, it will lose buoyancy, and the frustule will sink to the bottom. In areas of dense diatom populations, this can result in a sediment layer formed from a vast number of these discarded frustules. While the organic components of long-lived, their silica exoskeletons can remain in sediment layers for millions of years.
These layers of diatom frustules can be mined, and the material collected is referred to as diatomite or diatomaceous earth (DE). Depending on mining and processing, diatomaceous earth may be sold as chunks of stone or ground into a powder. Since the frustules (broken or whole) still have voids and holes they are much lighter and more porous than a solid piece of silica would be. Diatomaceous earth is used in a variety of ways: as a filtering material for swimming pool water, toothpaste abrasive, liquid absorbent, and as an important component of dynamite to name a few. It is also used for gardening.
Diatomaceous earth for gardening should be amorphous silica and contain little crystalline silica or active contaminants.
Chunks of diatomaceous earth may be used as a component in a growing medium. By virtue of the spaces, it holds both water and air well.
Dry powdered diatomaceous earth is used as a mechanical insecticide. It absorbs fats and oils from the insects exoskeleton while the sharp edges cut and damage. It can be applied by either sprinkling dry, or mixing with water to apply and then allowed to dry. While diatomaceous earth is not poisonous, breathing any dust can have detrimental health effects so precautions should be taken to avoid excess inhalation. It is frequently applied to the medium around the plant, but may also be used on plants themselves. If used directly on the plants avoid harvestable portions as it will leave a residue, and avoid spraying flowers to protect bees. Because it tends to dry up and blow away, reapply as needed.