Diatomaceous Earth is a naturally occurring soft rock consisting of the fossilised remains of diatoms; a type of algae. It is a superb all round insecticide and very capable of both preventing as well as eradicating most pests.
The powder works by killing pests in two ways. Firstly it is very abrasive and will physically cut and rip certain pests apart as they try to crawl on or through it. Secondly it damages the outer layer of their exoskeletons which in turn increases the evaporation of water from their bodies causing them to dehydrate.
Diatomaceous Earth is safe to use on your plants and will cause zero harm to them. The powder can be applied in a number of ways.
TOP DRESSING GROWING MEDIA
Apply a fine layer of powder to the top of your media. This is particularly useful for pests such as Fungus Gnats as it prevents them laying their eggs as they cannot penetrate through the powder. Likewise for instances where their larvae are already present in your pots, the powder will kill them or failing that will kill the adult gnats as they try to fly from the medium once fully grown.
APPLYING TO LEAVES
The powder can also be applied directly to your leaves for pests which are located on the plants themselves. The bottle can simply be squeezed over them causing a fine 'mist' of powder to fall on the leaves. For larger areas the powder can also be diluted into water and and used as a spray.