Imagine the fossilized skeletons of TRILLIONS of microscopic, single-celled aquatic plants, compacted and preserved over millions of years. It’s called ‘diatomaceous earth’ – the fossilized remains of unicellular fresh water plants called “Diatoms.” But this stuff is not just of interest to geologists. It also a lightweight, porous, sterile (through heat treatment), non-toxic, and safe horticultural growth media. Savvy gardeners who grow in soil, coco, clay pebbles, or other ‘loose’ media are experiencing far more vigorous growth by throwing some Diatoms into their mix. So how exactly do they do it?
WORDS: Everest Fernandez
Diatoms have been part of our planet’s ecology since prehistoric times. Over millions of years, their remains have accumulated into large diatomite deposits. These diatoms are mined and rendered into a fine, white powder. Natural diatomite is comprised of approximately 65-80% silicon dioxide, 14-18% aluminum oxide, and small amounts of various other oxides including iron, calcium, potassium, titanium, manganese, and phosphorus. Natural grade diatomite is known as ‘Diatomaceous Earth’ (DE) and is often used as a soil amendment and organic pesticide (more on that later!). Diatoms comes from both salt water and fresh water sources, but we’re only interested in fresh water diatomite for horticulture. The salt water DE has a really high salinity level that’s not suitable for plants.
Organic Pest Control
DE may feel like a smooth powder to human hands, but it’s a totally different story if you happen to be incarnated as an insect. When you look at DE under a microscope it resembles a random pile of tiny razors. These ultra-sharp edges cut through an insect’s protective covering, sucking all the moisture out of them until they die! If an insect is stupid enough to try to eat DE this delightful process occurs from the inside out! So aphids, thrips, earwigs, silverfish, slugs, snails, nematodes and fungus gnats beware! You’re on DE’s hit list. Our friendly earthworm is safe from DE’s wrath, however, which is good news all round. DE is less effective in more humid conditions as its moisture-sapping qualities are tempered by the moisture in the air. Many gardeners don’t even bother mixing DE with their soil mix, instead preferring to sprinkle a shallow layer of diatomaceous earth on top of their soil or coco.
Diatomite and Hydroponics
Our fossilized friends are also available in the form of small rocks, rather than a fine powder. These have been heat treated and sterilized. We are aware of three brands on the market at the moment. One is from a place called Maidenwell in Australia, branded “Diatomite.” Another is from the Andes in South America, branded in North America as “Silica Stone.” The same material that is used to create “Silica Stone” is branded as “Diahydro” in Europe. All work well as a hydroponic growth media. Silica Stone / Diahydro stays a little more moist than Diatomite so it requires fewer watering cycles – this is because it has a larger percentage of silica (94%+ compared to 84% for Diatomite), hence the pure white color and the greater absorbency due to increased porosity. You can purchase all brands in various granule sizes. It’s generally recommended to go for small granules of 3/16 to 9/16 inch (2mm to 7mm) or medium granules of 9/16 to 5/8 inch (7mm to 15mm) for hydroponic applications.
So why should hydroponic gardeners be interested in this stuff? Well, it has all the hallmarks of a first-class growing medium. It’s absorbent, porous, long lasting, environmentally friendly, pH neutral, sterile, natural and reusable! As well as silica, it contains other elemental minerals that are essential for plant growth. The plants will uptake the silicate and grow into heartier, healthier plants with thicker stem walls. Manufacturers of the brand “Diatomite” cite that, in side-by-side tests, a 25% increase in production was observed when it was tested against clay pebbles on pepper plants. However, we recommend mixing it 1/3 or 50/50 with clay pebbles when growing in larger pots for increased aeration and a more varied rooting environment. Obviously adding diatomite to clay pebbles affects how you irrigate it. Diatomite holds more water so floods should be slightly less frequent – irrigations every 2-4 hours are advised. If top feeding via drippers using a 50/50 diatomite, clay pebble mix we recommend avoiding constant irrigation in favor of a 15 minutes on, 15minutes off cycle – easily implemented using a standard segmental timer.
Spare us the hype! What are growers really saying about it?
I know what you’re thinking. If this stuff is so great then why isn’t everybody using it, right? So we spoke to real growers who had used it … here’s what they said:
“Works great as a soil amendment. As a hydro media, I’d mix it with something else like clay pebbles as it stays too wet on its own.” – Harley
UGM says: If you’re using this media for the first time, try combining it with clay pebbles for increased aeration. However, we have come across experienced growers who tested it as a hydroponic growth media on its own in gravity fed systems and they found that NOTHING worked as well as small to medium sized DE rocks on their own. Wash it well first!
“If this stuff has microscopic razor sharp edges, couldn’t it damage fine roots?” – Diz
UGM says: The material is very sharp on a microscopic level, but we’ve seen no evidence to suggest that roots are adversely affected. This may be because plant roots grow slowly and the material is light enough so that there is never sufficient pressure or friction for the roots to be damaged.
“I don’t like all that powder in the bags, it will clog my pumps!” – Randy
UGM says: If you put a sponge filter on the intake pump with enough power you prevent this from happening. And remember, this stuff is also used as filtration aids so you really shouldn’t worry about clogging!
“It makes the nutrient solution go cloudy.” – Dan
UGM says: The diatomite particles (diatoms) do not dissolve in water. Even if the water turns cloudy, the material has not dissolved.
“Can’t I just add silicate to my nutrient solution by using a silica liquid product?” – Lisa V
UGM says: You’re absolutely right – you could! Remember that liquid silica additives can raise the pH of your nutrient solution so you may need to pay special attention to adjusting the pH to optimal levels.
Benefits
- High Silica Content – the slow release of silica promotes stronger, healthier plants that can mature more quickly.
- Absorbent – it can absorb up to 150% of its own weight in water.
- Air penetration – the microscopic porous structure of the granules provides aeration and effective thermal insulation to the plant’s root zone. These physical properties provide air movement and prevent root rot.
- Water Cycles – You can reduce the watering cycles to 5 minutes each, 4 times daily due to the retention of solution within the diatomite.
- Preparation for use – Before using, thoroughly saturate the diatomite for about an hour.
- Reusable – After use, you can thoroughly wash the diatomite and then soak in a dilute solution of bleach (1 tbs/gallon) or an algaecide for 24 hours before rinsing and reusing it.
More Usage Tips
- It can be used to replace perlite, clay pebbles, as well as other commonly used hydroponic growing mediums. You can use it in both pots and re-circulating systems. Simply place the growth media in pots in the same manner as you have used clay pebbles or other media of choice. Place roots or seeds in a safe and stable position.
- On both occasions we advise that the granules are rinsed through with water prior to use.
- When using in recirculating systems, there may be some dust which runs down into the nutrient solution. There is no need for concern. Actually Diahydro / Silica Stone / Diatomite are highly efficient filtration aids, so this means there will be no clogging or loss of flow caused by residual dust.
- In order to stabilize the pH, try running some neutral water through the media and measure out pH of the water that flows out. The pH should be somewhere in the region of 6-7. Once this pH measure has been established you should adjust the nutrient solution accordingly. A nutrient solution between 5.5-6.2 should be fine. For example, if the pH of the water run off the growth media is around 7 (extreme case), the solution should be brought down to around 5.5-5.6. Likewise, if the growth media is lower (e.g. 6.2) then the solution can be brought up to about 5.6-5.8. Desired pH should be around 6 in most cases.
Diatomite in Action
A picture tells a thousand words. So we’ll let them do the talking:
SPOT THE DIFFERENCE!
Same nutrients. Same feeding schedules. Same light and environmental conditions. The only difference? Diatomite. Oh, and hugely increased compact growth, shorter inter-nodal spacing and markedly increased overall yield. Get the picture?
Have you got an experience using Silica Stone / Diahydro / Diatomite or any other growth media that you’d like to share with us? Whatever you want to talk about, love it or hate it, tell us about it!