Diatomaceous Earth Insect Killer Repellant Gardening

Mined from ancient riverbeds and lakes, diatomaceous earth (DE) is the fossilized remains of prehistoric, freshwater phytoplankton or algae. Many years ago these single celled creatures, called diatoms, formed exoskeletons made up entirely of silica. Like the algae of today, diatoms were found in large colonies or "ribbons" in bodies of water.

As these creatures died and piled on top of each other over eons, the exoskeleton compressed to form the sedimentary rock diatomite.

When mined, this crumbly rock forms a soft powder. Initially diatomaceous earth was used industrially as a component of dynamite. When its abrasive qualities were discovered, companies began adding it to toothpastes and polishes. Diatomaceous earth is now widely used, from grain storage (as an anti-caking agent) to an ingredient in boat epoxy. Gardeners and homeowners commonly use the fine powdered form for controlling unwanted insect pests.

Natural Indoor Insect Pest Control
Natural Garden Pest Control

Color and types

The different colors of diatomaceous earth reflect the regional differences of diatomite deposits from all over the world. Varying in color from light grey to brown to white, diatomaceous earth is graded by the purity of silica and the amounts of other minerals. For 'food grade' DE, there must be no more than 10mg/kg of lead or arsenic.

The diatomaceous earth found on the retail market is available in two forms, pool grade and food grade. Pool grade is calcined or treated with high heat, which turns the silica dioxide into crystalline silica. This process emphasizes the filtering qualities of DE but makes it very harmful to the respiratory systems.

Food grade diatomaceous earth is a freshwater form of diatomite. Although it can cause slight lung irritation over long exposure, it's safe to use topically and is often taken as a health supplement. Homeowners and gardeners may be more familiar with food grade DE because it's inexpensive and an important tool in many pest management strategies.

How diatomaceous earth works

Though diatomaceous earth is considered a pesticide under the Pest Control Act, its effectiveness is actually mechanical. If you looked at food grade, uncalcined diatomaceous earth on a microscopic level, it would look like a multitude of tiny hollow cylinders covered in barbs. These barbs make a very effective deterrent against a broad spectrum of insects.

As an insect or bug treads across the powder, the tiny barbed cylinders penetrate the waxy coating that covers the insect's body. This creates wounds that let body fluid out. The porous nature of the powder also makes it absorbent. This means diatomaceous earth works in two ways, both injuring the pest and drawing out fluid to dry and kill the insect. Death does not happen on contact, but over a short period of time. If left undisturbed, diatomaceous earth can be effective within 24 hours, though better results are usually apparent after five days.

Type of Insect	Apparent Results
Bed bugs	24 hours to 5 days
Darkling beetles	7-21 days
Silverfish	7-14 days
Black or red ants	24 hours

DE is effective on many more insect types than on the chart above. Most common household insect pests, including fleas and cockroaches, will be controlled or eliminated by persistent application of DE.

Several factors will influence the success of diatomaceous earth: the type of insect, size of infestation, temperature, and humidity. Because diatomaceous earth is so absorbent, excessive moisture or rain can limit its effectiveness. DE will be less effective if applied too thinly; better to lay out 'lines' of DE rather than dusting an area.

Additionally, all insects are susceptible to DE, even the good ones. In gardening, this means it's essential to limit your application to wherever the pests exist and not where beneficial insects dwell. Don't apply to flowers or known ground beetle habitat.

If applied correctly, diatomaceous earth is:

Non toxic to pets or humans
A versatile pest management tool
Easy to find in most communities
Inexpensive

Using diatomaceous earth to control insects in the home

With any pest management situation, it's important to know the behaviour and habitat of the insect you're trying to control. Before applying DE, gather a little background information.

For the best results:

Identify the pest and their habitat. For silverfish, ants, roaches, pill bugs, carpet beetles, roaches, fleas, bed bugs, spiders and flies, look in the discreet places where these bugs can hide, such as areas the vacuum or brooms can't reach. Be sure to check behind furniture, fridges, crevices where floors meet walls, at the back of cupboards, and along windowsills.
Using a teaspoon, set out the DE in lines that insects will be likely to cross. The more DE they come into contact with, the faster they'll die. Leave these lines in place. Do not sweep, vacuum or get wet. Apply DE strategically behind or beneath furniture and appliances, with an eye toward places the vacuum does not reach.
Insects like ants may change routes if they sense a dangerous substance. Monitor the insect's behavior and follow up your initial application if you discover they're not crossing the existing paths of DE.
Don't apply generally or sprinkle lightly. Too thin of an application will result in not enough contact with the insect. Ensure you are making thick lines crossing their routes of passage.

Controlling bed bugs with diatomaceous earth

Bed bugs are a rapidly increasing problem and can be very difficult to manage. This is due in part to their increased resistance to chemical pesticides and their ability to hide in difficult to reach places. Although they can exist alone, they'll most often be found together in larger numbers. Examples of bed bug hideouts are under the box spring, in cracks of the bed frame, the stitching in suitcases, and even inside electrical sockets. Apply DE to passages wherever bed bugs travel. When DE is used with a plant based bed bug spray and strict sanitation measures, control is achieved even more rapidly.

Controlling fleas

The cat flea, Ctenocephalides felis, is the most common flea in North America. Favoring cats and dogs, this bloodsucking insect reproduces quickly and can go for long periods without a host. Cat flea activity is triggered with an increase in carbon dioxide or vibration. Pet beds, carpets, and furniture are susceptible as areas where fleas will lay dormant.

Disrupt the cycles

The common distribution of fleas is 50% eggs, 35% larvae, 10% pupae and 5% adults. Though cleaning your pet is essential in a flea management program, this method alone is useless. The majority of the flea population lies in wait mostly on pet beds and carpets. It's essential to vacuum regularly around the places that fleas frequent to disrupt the lifecycle by eliminating the developing juveniles and eggs. Dispose of the vacuum contents after each clean. Follow with an application of diatomaceous earth in the following places:

A heavy dusting under the pet's bed
Under cushions where your pet frequents
Carpets where you suspect fleas could be residing

Using diatomaceous earth between vacuuming provides ongoing flea control for those pests missed in the cleaning. One pregnant female can lay up to 5000 eggs in her four month lifetime, and a dormant flea egg can remain viable for up to a year. After application, DE remains viable in the fabric or carpet for months to come in case those eggs do hatch.

For persistent flea problems, we recommend using electric flea traps along with a program of applying DE. Locate the trap(s) in areas of highest flea concentration and apply the DE more broadly throughout the premises.

Diatomaceous earth for controlling insect pests in the garden

Garden pests are controlled most successfully with DE when the product can be kept dry and out of the way of beneficial insects.

For bulbs	Just prior to planting, dip and coat entire bulb or existing stem in DE to address any dormant bulb thrips, borer, or mites.
In the greenhouse	Sprinkle a perimeter barrier of DE around seeding trays for pill bugs and around the base of small plants to protect against earwigs.
In the garden	When plant leaves are dry with a forecast of good weather, dust plants with diatomaceous earth to help control asparagus beetle, Mexican bean beetle, potato beetle and cutworm.
For aphids	Dust under the leaves and directly into infestations of aphids on cabbages, broccoli, kale, and cauliflower.

Avoid putting DE directly on flower heads because bees are especially susceptible to the effects of the dust.

Diatomaceous earth is probably the most overlooked insect pest control available for residential and garden use. Most people have never heard of it, yet it has a longstanding track record for safety and effectiveness. DE is abundant, natural, effective, long-lasting and very inexpensive, with little to no toxicity to the surrounding environment when applied properly. DE should be the first line of defence in everyone's pest control arsenal. In many homes, DE may be the only insect pest control measure you may ever need.

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About the Author

Jessica Dawe
Jessica Dawe owns a garden center and has been practicing integrated pest management and permaculture since graduating in 1995 with a degree in horticulture.