Diatomaceous Earth For Organic Gardening

One of the coolest things about diatomaceous earth (DE) is that it was originally plankton, meaning it went from being an organic material to a mineral. But how could that be?

And what exactly is DE?

How DE Came to Be

Well, in the time of dinosaurs, give or take an epoch, plankton flourished in lakes and seas. These plankton species multiplied to countless proportions, especially during volcanic periods, when they consumed carbon dioxide (CO₂) and extracted silica from the water.

The silica was ingested to support cell walls that grew into beautiful, microscopic, porous silica structures. These plankton bodies were so porous that water flowed through them, providing a continuous supply of nutrient absorption.

When they died, they sank to the bottom and accumulated in vast numbers as sediment. The skeletal remains of these structures are called diatoms. Eventually the waters receded, the topography changed, and these huge deposits of diatoms were discovered and named diatomaceous earth.

How Do We Get DE?

Today, DE is mined much like sand or gravel. (For the record, DE contains amorphous silica, which is the safe kind.)

Of course, DE is not one universal product. In the green industry, natural DE powder is used for insect control, while DE aggregates improve soil function for all types of plant applications.

Natural DE powders are different from powders used for filtration purposes, which are combined with other ingredients and kiln-fired to create better properties for separating particulates.

Natural DE powders have no additives and, as mentioned, are designed for use on insects and plants. Under a microscope, powdered DE is made of a whole lot of broken diatoms.

To an insect, these are extremely sharp, hard edges that resemble a minefield of broken glass, cutting and abrading away their waxy layered exoskeleton.

Insects get severely injured in their joints and bodies. They desiccate and they die. They can't build up immunity because it is a mechanical mode of action.

Gardening Applications for DE

Diatomaceous earth powder is blended into potting mixes to control insects at two to three per cent by volume. It can also be applied topically on the ground, applied to foliage as a dust with a puff bottle or hand-cranked blower, or mixed as a wettable powder to spray onto the top and underside of leaves.

It is safe to use on food up to 24 hours before harvest, but just be sure to always wash your edibles before eating them.

Even food-grade DE powder, which can be used in food production, such as mixing it with grains during storage to keep bugs away, shouldn't really be eaten (though we hear people use tiny amounts as a supplement and testify to results).

Diatomaceous earth in aggregate form is very versatile, comes with some compelling research, and is challenging traditional soil component choices in the greenhouse, nursery, potting soil, and hydroponic markets.

Aggregates enjoy wide acceptance for rooftop gardens, outdoor gardens, structural soil, sports fields, landscapes, and bioswales. They can also be used in lieu of or in combination with peat moss, and mixed with sand for golf green construction.

Physical Properties of Diatomaceous Earth

Diatomaceous earth aggregates have unparalleled physical properties designed by nature. They are 82 per cent porous and very absorbent (up to 142 per cent their weight in water), giving them great potential to influence water conservation.

To help retain nutrients, they also have a cation exchange capacity of 27. Absorbed water and water-borne nutrients are readily released and available to plants.

Aggregates show impressive measurable increases for improved infiltration rates, water-holding capacity, plant-available water, and increased air and water exchange.

They also increase porosity, serving as additional reservoirs of pore space where air and water can exchange into, and out of, the granules, unit for unit, as moisture fluctuates. This creates a much more interactive soil media for root growth, water uptake, and nutrient uptake.

Aggregates promote easier establishment, excellent plant health, and legendary root mass due to increased air capacity and circulation, coupled with consistent reports of silica uptake.

They are also pH neutral, and because it is a mineral source of pH, it tends to stabilize pH in soil and hydroponics. They reduce compaction, are essentially permanent, and perform long-term.

Remember how water flowed through the living plankton structures?

The pores in DE aggregates have been identified by studies at the University of Augsburg as the same pore size that determines plant-available water (plants have an easier time getting water from pore spaces than from water as film on soil particles).

Perhaps you've heard that if you want to reduce irrigation, just improve plant-available water.

Well, DE aggregates have more plant-available water than peat moss, four times more than compost in native soil, and 90 per cent more than calcined clay from water release curves.

This is worth considering if you want soil moisture uniformity and controlled wetting and drying, and if you believe in conserving water.

When it comes to soil water pores, there are three types: larger, free-draining pores; appropriately sized, plant-available water pores; and smaller, less-available water pores.

Diatomaceous earth pores are invisible to the naked eye, so visible pores in other media indicate free-draining pores with less water retention and less plant-available water.

When we scan other inorganic choices for soil mixes and hydroponics, we see perlite, pumice, and clay spheres. (Those once organic, DE aggregates are inorganic amendments due to the silica transformation into a porous shape and from the kiln firing that reduces any organic fraction.) These other choices are all assumed to be porous, but the active porosity is skin deep.

The Many Ways to Use Diatomaceous Earth in the Garden

Only the surface pores can interact and contribute to physical activity within a mix, as the internal pores are isolated air bubbles trapped within mineral bodies. This represents a considerable amount of soil mix volume that is limited from interacting with air, water, roots, and other soil components.

Another advantage of DE aggregates is that they do not float. Aggregates come in a variety of sizes: larger grades (3/8 to ½ inch), which are suitable as inorganic hydroponic mediums; coarse and medium grades (3/8 to 1/8 inch) for soil mixes and potting mixes; and a fine grade (like large sand) for use with potting soils to improve soil performance, with the added potential for insect control.

The Many Ways to Use Diatomaceous Earth in the Garden

DE and Hydroponics

Some veteran growers may remember large DE chunks for hydroponics. Well, that super-size aggregate is available again and it rivals the best current mixes and inorganics.

You can mix it at either 100 per cent by volume, or at 40-60 per cent and mixed with an organic. Users at these rates also remark they have less bugs.

Incorporating medium size DE aggregates into native soils or soil mixes outdoors is a great way to ensure successful establishment of every plant. They provide permanent porosity to hard or sticky clay when mixed in at 10-15 per cent by volume.

It provides excellent drought relief in hot climates and is suitable for turfgrass, trees, shrubs, gardens, and flowers.

Moreover, each plant will enjoy an environment that is physically conducive to proper availability of water, nutrients, and pore space to grow.

For indoor containers, DE aggregates can be applied at 15-20 per cent by volume. Again, this will increase the water-holding capacity, homogenize moisture content throughout the pots, provide more plant-available water, and reduce watering needs.

Outdoor containers with DE in the mix will experience similar results, but with higher contrast between moisture levels because of increased evapo-transpiration.

Final Thoughts

Yes, DE is kinda cool. The porous structures are reminders of how they formed, how they work, and their modes of action, offering support and well-being for plants and soils. Best of all, they offer ideal solutions for plants and soils.