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RayR April 16, 2012 12:56 AM

Diatomaceous Earth as a seed starting medium
3 Attachment(s)
This experiment started in January when I was wondering how Diatomaceous Earth would work as a seed starting medium. I know that DE is used by some folks in hydroponics as a growing medium, it is also used by some folks in Bonsai, and studies have been done using DE as a soil amendment, but I’ve never ran across anyone who has used it as a seed starting medium. So my curiosity forced me to try it. I had some Blue Ribbon D.E. Premium Cat Litter manufactured by the Moltan Company which I have used as a potting soil amendment, so I had something to start with. From my research on DE I found that the PH of DE can vary depending on where it is mined, so I did a PH test with my digital PH meter and the Moltan product came in at a PH of 6.8 which was perfect, the same as a standard peat based seed starting mix. My first experiment was with Llia Onion seed and the results were very impressive, I grew some very healthy onion seedlings with no problem.
My second experiment came in mid-March with tomato seeds. I found that Moltan makes the same DE product sold as an oil absorbent called UltraSorb which I found right down the street at the local AutoZone in a 15lb bag for $5.99. The only difference between UltraSorb and the kitty litter was the granule size, the UltraSorb is a much less coarse granulation (more like coarse sand), which was easier to work with.

I seeded 24 Brandywine and 24 Black Krim, half in Jiffy Seed Starting Mix and half in DE.They were bottom watered with distilled water, put on the heat mat under lights and given no nutrients until they developed their first true leaves. The germination rate was exactly the same. Here is what they looked like today. See any difference?

PaulF April 16, 2012 11:20 AM

I love experiments. Nice job. Thanks.

janezee April 16, 2012 05:07 PM

That is just wild! I love it!

RayR April 18, 2012 12:44 AM

I'll let these go a little longer before potting up, but I'm seeing little difference in growth other that the noticeable bigger leaves on a number of the Brandywine seedlings on the DE side.

I've got some DE experiments with peppers and basil in the works too, so we'll see what develops there.

tuk50 April 18, 2012 10:20 AM

Ray, does it wick up like peat, if watered from the bottom?

RayR April 18, 2012 11:13 AM

It wicks up much faster than peat, it also retains the water very well over time.
It also has a respectable cation exchange capacity, so it holds nutrients in the medium.

Heritage April 18, 2012 04:46 PM

Ray, thanks for posting. I think we need a whole sub-forum for experiments!


janezee April 18, 2012 06:54 PM


Thanks so much for this. I love that you though of this, tried it, and posted!

I think I'll try this with the seeds I got from Carolyn. I have 1 each left, and I already know that they don't like my other potting medium. Out of 5 varieties and 27 seeds sown, only 2 emerged after 12 days. I haven't given up hope, but I'd love to see if I get germination on those singles.

RayR April 19, 2012 01:56 AM

Janezee, it can't hurt to change your seed starting medium when you have some troublesome seeds. Although I haven't had much trouble with tomato germination this year, I have had some issues with certain pepper varieties. In my first sowing of peppers, with Chinese Giant bell peppers I got zero germination with 9 seeds sown in Jiffy mix. In my second sowing I planted 12 seeds in Jiffy mix and 12 seeds in DE. I got 5 strong seedlings pronto in DE and 2 in Jiffy mix. Go figure.

janezee April 19, 2012 03:22 AM

Sounds good, Ray. It can't hurt at this point.

RayR April 27, 2012 10:44 PM

Pepper Experiment
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This is my first experiment with Pepper seeds in Diatomaceous Earth. I seeded 18 Chinese Giant Bell and 18 Hungarian Hot Wax, half in DE and half in Jiffy Mix.
My stubborn Chinese Giant seed did pretty well in the DE with 5 strong seedlings, but only 2 in the Jiffy Mix, the germination for the Hungarian Hot Wax turned out equal with 7 seedlings in each medium.
What is more important is the rate of growth, both varieties of peppers are growing much faster in the DE, Any ideas why?

Tracydr April 28, 2012 11:58 PM

Could DE be used as a portion of a potting soil mix? If so, which porting and what percentage? Not for earth boxes.

RayR April 29, 2012 03:01 AM

[QUOTE=Tracydr;271347]Could DE be used as a portion of a potting soil mix? If so, which porting and what percentage? Not for earth boxes.[/QUOTE]

Absolutely, I know some folks here on TV have used it to amend their container mixes as have I. I'm even trying it as an amendment to my garden beds this spring.
It can be used alone or in combination with perlite. It's very light in weight, but not quite as light as Perlite. Both are composed of mostly silica, Perlite is manufactured by expanding hydrated volcanic obsidian glass, DE is a natural deposit, the fossilized silica skeletons of prehistoric diatoms. Both are made of mostly stable and inert amorphous silica, but DE contains a small amount of soluble silica which can be utilized by plants.

How much to use? I don't know exactly, that would take some experimentation itself.

There is a commercially made high end potting mix that is made locally here in Western NY called [URL=""]Just Right Xtra All Organic Potting Mix[/URL] which doesn't use any Perlite at all in the mix, but they use a very coarse horticultural grade DE that is also the same type that is used as a medium in hydroponics.

RayR May 4, 2012 07:02 PM

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The Tomato plants were starting to look unhappy in those small cells, so a few days ago I started potting them up. As you can see from the pictures, the roots of the tomato seedlings grown in the DE were long, thicker and fibrous. It was a lot easier to separate the seedlings in the DE than in the Jiffy Mix. It took a lot of massaging of the Jiffy Mix roots to minimize damage so I could get a fair comparison.
I think next time I do this, bigger cells would work better. I didn't expect the roots of the plants in the DE to get this huge. Anyway they are all looking much happier now that they are separated and potted up with lots of room to stretch.

MeWhee May 4, 2012 07:14 PM

As an aside, we have a small section of our backyard tomato garden which borders our fairly large pool filter/heater. Every six months or so (when cleaning the filter itself) we fold in some of the used DE - along w/ all the organic nutrients included in the mix and have found it truly beneficial to the plants.

They seem to do considerably better than the section which hasn't received the mix and the neighbors garden who doesn't have a pool.

Will in So. Cal.

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