On his radio program of Sunday, August 17, 2003, the "Dirt Doctor" backed off of what he has been claiming for several years when he told his listeners,  "I’m just not much of a fan of using diatomaceous earth for insects anymore because it just doesn’t work very well. I do recommend using it as a food supplement."  Then a few minutes later he declared, "If it’s a humid day, that stuff (DE) doesn’t kill anything."

Since, for the moment, he still recommends it as a food supplement, the following (the original content of this page) is still pertinent in that context.

Howard Garrett, the self-anointed "Dirt Doctor," continually recommends diatomaceous earth (DE) for use as an "insecticide," as a soil additive, and as a food supplement for horses, dogs, chickens, and humans. And he says that feeding it to cattle will get rid of flies.

For control of a number of insect pests, he recommends dusting diatomaceous earth in flower beds, on the lawn, and on the carpet inside the home (even though he generally agrees it is dangerous to breathe).  He recommends its use as a soil additive because, he says, "it contains all sorts of trace minerals, some of them very rare."

To test how much he really knows about diatomaceous earth—without arguing about the merits of its use, pro or con—let’s review a sampling of the actual statements the "Dirt Doctor" has made.  And let's see if they don't bear out the words of Daniel Webster, who said, "Falsehoods not only disagree with truths, but usually quarrel among themselves."

5/28/93: "Diatomaceous earth (DE) is approximately 23 percent calcium, 12 percent silicon and 57 percent carbonate; it’s loaded with trace minerals. It is basically skeletal remains of microscopic algae. The razor-sharp edges of the broken remains scratch insects, causing them to dry out and die."

8/24/93: "The white cliffs of Dover are diatomaceous earth, which are skeletons of algae, so are probably plant life."

12/8/95: "DE is made from the skeletons of microscopic one-celled floating plants called diatoms; they’re close kin to algae. These skeletons have accumulated for centuries under huge lakes or oceans. DE is mined from these natural deposits…Saltwater and fresh water DE are appropriate for horticultural or animal use. These types of DE are ground into powder and bagged; they’re not treated or processed in any other way."

"If the label of the product you buy says the DE contains 85 percent silica [sic] dioxide, 10 percent inert ingredients and 5 percent moisture, don’t be alarmed: This content information means you have the pure, natural DE. The inert ingredients are the trace minerals, and the 5 percent moisture is the water."

"Use DE as a soil amendment, too. Even though a breakdown of inert ingredients usually measures DE’s sodium content at about 5 percent, don’t worry about that; some sodium is necessary to control disease organisms in the soil. It also contains 2 percent iron along with smaller amounts of other trace minerals [sic] such as titanium, boron, manganese, copper and zirconium."

"Check the labels on the dry food products in your cupboard. You’ll notice a common ingredient called silicone [sic] dioxide. That means diatomaceous earth. I don’t have to talk you into feeding it to your animals or eating it yourself—because you already are."

3/8/96: "DE also is a good mineral supplement for the soil. DE is loaded with trace minerals, and some of them are very rare."

4/26/96: "The white cliffs of Dover are DE…DE comes from large strip mines in several places in the Western United States. DE deposits form from the remains of single-celled diatoms that live in oceans and large lakes. Large solid chunks are ground into powder and screened to a uniform size…It eliminates internal parasites by improving the digestion and mineral intake."

2/9/97: "DE is used as an anti-caking agent in many foods. That’s the silicon dioxide, the amorphous DE mined right out of the ground. It’s loaded with trace minerals and is a natural vitamin supplement. Amorphous DE is less than 2 percent silicon dioxide, and the people who mine it aren’t even required to use masks."

8/31/97: "Diatomaceous earth is a dust from volcanoes. The dust attaches itself to microorganisms in the sea. It’s loaded with trace minerals. Taken internally, it’s mainly a dietary supplement; it helps digestion. The result is control of internal parasites."

4/17/98: "It (DE) consists mainly of the powdery, siliceous shells of ancient single-celled algae."

6/28/98: "DE is an excellent soil amendment; it’s full of trace minerals."

8/16/98: "Amorphous DE contains only one percent or less crystalline silica [sic] dioxide. People who claim otherwise just don’t know what DE is."

11/13/98: "DE is about 3 percent magnesium, 80 to 90 percent silica (silicon dioxide), 5 percent sodium and 2 percent iron…Take precautions when using diatomaceous earth. It is dusty, so wear a mask or stand downwind [sic] when applying it."

Texas Organic Vegetable Gardening (1998):   "Natural diatomaceous earth is approximately 5 percent aluminum, 5 percent sodium, 86 percent silicon [sic]."

3/14/99: "Diatomite is swimming pool DE and has been calcined, that is, partially melted. And when it’s calcined, the crystalline silica level goes from one percent or less to about 50 or 60 percent. If diatomaceous earth has been processed in any way—other than just dug up out of the ground and bagged—I don’t recommend it."

4/14/00: "Pool DE has been partially melted and in some cases chemically treated...contains a high level of crystalline silica [sic] dioxide that is dangerous to breathe."

7/22/01: "Swimming pool DE has been calcined; that is, it's been heated to 2,000 degrees."

6/15/02: "Natural, acceptable, fresh-water diatomaceous earth says on the label it has 85 percent silica [sic] dioxide and 15 percent water and inerts."  (And he repeated this same bit of information a year and a half later during his radio show on 1/11/04.)

"Seaweed, mixed with DE and zeolite, those natural volcanic materials, can be fed to pets."  [Natural volcanic materials?]

I ask you...
Do these sound like the words of someone who knows what he is talking about? In the strange world inhabited by the "Dirt Doctor," DE consists mainly of siliceous shells, or it is skeletons or basically skeletal remains of single-celled, plant-like diatoms, which are either algae or are kin to algae. Or DE is volcanic dust. Take your pick.

And, in that same world, natural DE is 12 percent silicon, or it’s 85 percent silica [sic] dioxide, or 80 to 90 percent silica, or it (natural, amorphous DE) contains less than 2 percent silicon dioxide, or even 1 percent or less. Take your pick.

Also, pure, natural DE contains either 10 percent or 15 percent inert ingredients, but only 5 percent of 10 percent (one-half of one percent) is sodium. Or it contains 5 percent sodium. Take your pick, but don’t worry about using it as a soil amendment because "some sodium is necessary to control disease organisms."

He ignores or simply doesn’t know that one-half of one percent is 5,000 parts per million (ppm), and 5 percent is 50,000 ppm. It makes little difference which one applies, since plants with a high tolerance for sodium will begin to suffer when the concentration exceeds 300 ppm, and plants with a low tolerance for sodium can’t stand more than about 100 ppm.

And 5 percent aluminum is no better, since 50,000 ppm of this metallic element would render phosphorous unavailable and would be extremely toxic to plants in acid soils.

The term "amorphous" means "noncrystalline and without form." But natural DE consists primarily of the exoskeletons of microscopic golden algae, known to the geologist as "diatoms." These perfectly formed, opaline shells (frustules) are almost pure silicon dioxide, the same chemical formula as quartz. And they are naturally sharp-edged; they don’t have to be broken.

On the other hand, if "natural" DE contained only 1 to 2 percent silica (which is silicon dioxide), as the "Dirt Doctor" has said, then it couldn't have any significant insecticidal properties and would be labeled as something other than diatomaceous earth.  And I'd sure want to know what that other 98 to 99 percent was before I ate any of it.

Most DE has indeed been calcined or otherwise treated to remove impurities and noxious compounds.  But that process, by definition, involves heating only to a dry, powdery state -- in an oxidizing or reducing environment and at temperatures below the melting point of silicon dioxide -- for the purpose of removing impurities. So, to this point, none of the silica has been "partially melted."

Swimming pool DE is, as the "Dirt Doctor" says, heated to approximately 2,000 degrees Fahrenheit (actually, 900 to 1,100 degrees Celsius). But this isn't calcining. It's a process properly known as sintering; whereby the tiniest frustules meld together to form larger particles, which decreases the overall size distribution and creates a better filter medium.

[Note: Silicon dioxide, amorphous or crystalline, has a melting point of from 2678 to 3110 degrees Fahrenheit (1470-1710 degrees Celsius).   Natural diatomaceous earth is calcined at approximately 1800 degrees Fahrenheit to remove impurities.  For use as a filter medium, the purified product can then be sintered at a temperature of approximately 2000 degrees Fahrenheit in order to create a more uniform grain size.  Neither process reaches the melting temperature of the mineral.]

Amazingly, in his newspaper column of August 10, 2001, the "Dirt Doctor" wrote about swimming pool DE being highly crystalline and then said, "This modified product won't break down in the lungs."  Surely, he doesn't mean to imply that other forms of diatomaceous earth will "break down" in the lungs.  But, with this man, one never knows.  He has, after all, said that the miners of diatomaceous earth are so safe they don't even need to wear dust masks.

Yet studies of the health risks to miners at the large diatomite deposit near Lompoc, California, indicate otherwise.  Published reports state that workers face not only a measureable risk of "silicosis and associated restrictive lung disease," but also a "significant risk of mortality from lung cancer."   (So DE sure doesn't sound like anything I'll be dusting around on the inside of my house.)

"Diatomite" is the mineral name geologists give to natural deposits of diatomaceous earth, not to any form of processed DE.  More than half of the commercial diatomite in the U.S. comes from the site near the city of Lompoc.  There, large volumes of DE are mined, processed, and then segregated into three grades: filter grade, agricultural grade, and food grade, something the "Dirt Doctor" obviously doesn't know.

One published mineral analysis of a natural diatomite shows a content of 65-80% silicon dioxide, 14-18% aluminum oxide, and lesser amounts of the oxides of iron, calcium, potassium, titanium, manganese, and phosphorous.  It also shows concentrations of from 2 to 400 parts per million of numerous contaminants, including antimony, arsenic, barium, boron, bromine, cadmium, cesium, chlorine, chromium, cobalt, copper, fluorine, gallium, lanthanum, lead, molybdenum, nickel, niobium, praseodymium, rubidium, samarium, scandium, selenium, strontium, tantalum, thorium, uranium, vanadium, Yttrium, and zirconium.  (The "Dirt Doctor" will actually eat this stuff as dug from the ground, yet he repudiates the use of Ironite™ as an iron supplement for soils because it contains something less than one percent of inert arsenic and lead.)

In any case, you should certainly ascertain that the "pure, natural DE" the "Dirt Doctor" recommends you use as a food supplement is actually a food grade product -- or at least is an agricultural grade product with most of the potentially noxious contaminants removed. Otherwise, if it's, as he claims, DE that's just "dug up out of the ground and bagged," eating it isn't much better than eating ordinary dirt.

And, in that same regard, the chief scientist at the largest supplier of food additives in Dallas insists that the silicon dioxide listed on food labels is an entirely synthetic, manufactured product, related only by chemical formula to natural diatomaceous earth. He says that most of it is produced by the J. M. Huber Corporation.  Nevertheless, the "Dirt Doctor," as late as December 21, 2003, continued to claim that DE is used as an anti-caking agent in "lots of dry food products."   Then he added, "Sometimes it's natural , and sometimes it's artificial," thereby turning quartz and every other variety of silicon dioxide into just another type of DE.

Lastly, the white cliffs of Dover are large deposits of cocolithic limestone (commonly known as chalk) and are composed almost entirely of calcium carbonate. They’re certainly not diatomaceous earth.  Nor are they any sort of volcanic dust.  But, then, neither is diatomaceous earth.