Diatomaceous earth after 18 months

Hi folks!

I’m moving a bunch of my nursery stock trees from containers --> grow bags --> raised beds today. Some of them (all bald cypresses) have been in 100% diatomaceous earth for ~18 months.

The DE was thoroughly screened, then thoroughly rinsed, before the trees went in. I live in Louisiana on the edge of zones 9a/9b; this substrate has experienced MAYBE one night below 32F. We get a lot of rain and the humidity is roughly 120% for eight months of the year.

Here’s what the bottoms of those containers and trees looked like today.


Some of that could be dust that I failed to wash out… but I think at least some of it is DE particles that have broken down.

Data for your consideration. :slight_smile:

(I have this suspicion that @BillsBayou might have additional data or insight.)


What type of DE were you using? I’ve been using it (Oil Dry) for a few years and haven’t experienced that kind of breakdown in any of my trees, including ones wintered outside here in Colorado.

Mine is NAPA Part 8822. I can’t help but wonder if DE is resistant to cold but not to some combination of heat/relentless moisture.

You can get slightly larger particles with the product from Grainger. It’s on my to-do list. I have it, but I ain’t got nuttin in it.

These are going into grow bags? What soil are you using in the grow bags?

A 2-3 year stint in grow bags in raised beds. Grow bags are roughly 50/50 pumice/organic (pine bark mulch and Black Kow).

Question about your prep in washing and sifting. Did you sift > wash > sift > wash over and over and over again? I have found that I need to do that until the water runs clear, otherwise you’ll get tons of dust still there. I got that suggestion from somewhere on da interwebs, but I’m not sure where.

Yes I did. I thought I was being Excessive. :confused:

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I have never worked with DE.
After you wash your DE, do you let it fully dry out before using? Does it become soft?
With Akadama, if it is not fully dry it is very soft and will break down when “chopsticking” during repots.
I have had bags of Akadama with moisture in them and it will be useless if I don’t dry it out.

Possibly, Colorado is relentlessly dry, so it could be the humidity that breaks it down so quickly.

Good thought – I haven’t historically dried the DE out after rinsing it. It could be that. It could also be the relentless humidity of the Gulf states. Or both!

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I just put my trees into DE this year. Yet to see what kind of results I get. Summer did feel a lot easier this year though, but I also got better fertilizer and was more cognizant of my watering. Dunno how much the DE helped in the big picture.

If I remember my research correct, almost all the stuff sold in the US is mined by EP Minerals. The only difference between where you get it is the particle size. The optisorb, the NAPA stuff and a bunch of others are essentially the same.

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I bought some from NAPA as well, but was hesitant to commit because I could crush particles w my fingers. Are there harder grades, or is anyone saying they’ve had success w the same (Oil Dry) product? Particle size seems to be perfect. I am surrounded by some nay-sayers, and I want to experiement with it so I can say, “I told you so.”

The stuff is incredibly cheap! Love that aspect of it.

I’m watching the soils stream again. Partially because I’m freaking out about the upcoming repotting season. I have so many to repot because I’m an idiot and went on a nursery stock rampage. :weary:

This past season I’ve been working with DE and it’s been hit or miss. I figured I should share my experience and hopefully others will as well…and then I stumbled upon this thread lol.

I sourced my DE from the usual suspect. That being Napa auto parts stores. So far I’ve used DE in my grow bags at a 2:2:1 (bark “top soil”, DE, mushroom compost) mix, 1:1 pumice to DE mix in a pot, and 100% DE in a pond basket.

Grow bag results: Hard to say. Plants look like they’re doing well. The plants in question are 2 bald cypress, 1 southern live oak, 1 hinoki and 1 carolina sapphire cypress. Honestly, in the grow bags the bark “top soil” (cheap stuff from Lowe’s that’s mostly bark) probably handles the job of water retention and CEC. I used the DE in lieu of pumice because, frankly, I didn’t have any. I think that perlite would be a better substitute for pumice than DE in this mix.

Pumice/DE results: My wife found some maple saplings around our yard. I believe red maple? Idk. She wanted to grow them, so I gave her a mix of 50/50 pumice and DE substrate. Those little saplings have done well. The question is why. :thinking: Would they have done just as well in 100% pumice. I did not fertilize them, so the CEC component of the mix that is presumably provided by the DE should not be a factor. I’m going to attribute it to the larger grain size of the pumice thus a better balance of oxygen and water. And here’s why…

100% DE results: Seeing the previously mentioned maple saplings do well inspired me to collect more from around the house with the hopes of making an eventual group planting. You know because, as Bill Valavanis mentioned, beginners want to jump straight to creating a forest composition lol. Anyway, I bought a couple pond baskets and filled them with DE. No pumice to be found, so I did what I had to do. DE by itself is very interesting. While it may appear wet on the surface when you water it the DE underneath could/will be bone dry. I think it has to do with the flat nature of the granules. Once they get wet the water just sheds off to the sides. It takes a lot of watering to really fully saturate the entire container. The same surface that’s fighting you also seems to dry out quickly when compared to the interior of the container. Especially with no top dressing. So now you’re left wondering whether or not you actually need to water. A quick dig into the substrate and you’ll see that it’s just the surface layer that appears dry. The saplings I’ve grown in the DE are alive and well, but are not thriving as well as the saplings in the 1P/1DE mix. They’ve grown half as much as the P/DE saplings. This is either due to under watering from not being able to fully saturate the substrate or overwatering due to thinking that the substrate was dry since the top layer goes pale white relatively quickly when compared to the interior.

All in all, I think that DE when mixed with other substates can be a viable alternative. Perhaps a larger grain of DE that’s more round in form factor would be better as well and allow for a more even distribution of water and oxygen. Sorry for rambling. I would love to hear what others have to say. I’m far from any sort of expert. These are just my observations at this point.

PS: Wash, wash, wash and wash again when working with DE. To say that it’s dusty is an understatement. The washing process is what first clued me in to the fact that getting water to penetrate it is difficult. That means washing in small batches. :weary:

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I just started to use some DE this past spring so I don’t have any data on how well it hold up. However, I did some sieve analysis and water absorption on 3 different materials below. I found that the NAPA had a fair bit of dust.

Down to Earth Diatomite Rock - Marle Worm Growers
$26.95 for 25 lbs
Sample was warehouse dry when screened Water Absorption - med & small particles
Wt (g) Wt %
Large +3 mesh 5 0.21% 0% Dry/moist 270
Medium +4 mesh 945 39.79% 40% Wet 535
Small +8 mesh 1410 59.37% 59% % Absorped 98%
V. Small +16 mesh 10 0.42% 0%
Dust -16 mesh 5 0.21% 0% Most sank immediately, all sank 2+ hrs
Good choice for medium particles

O’Reilly’s Floor Dry
$11.95 for 25 lbs
Sample was showroom dry when screened Water Absorption - small particles
Wt (g) Wt %
Large +3 mesh 0 0.00% 0% Dry/moist 250
Medium +4 mesh 0 0.00% 0% Wet 540
Small +8 mesh 905 61.15% 61% % Absorped 116%
V. Small +16 mesh 550 37.16% 37%
Dust -16 mesh 25 1.69% 2% Most sank immediately, all sank 2+ hrs
Good choice for small particles

NAPA Oil Dry
$9.95 for 24 quarts
Sample had been swept from floor Water Absorption - small particles
Wt (g) Wt %
Large +3 mesh 0 0.00% 0% Dry/moist 100
Medium +4 mesh 0 0.00% 0% Wet 263
Small +8 mesh 100 21.60% 22% % Absorped 163%
V. Small +16 mesh 293 63.28% 63%
Dust -16 mesh 70 15.12% 15% Most sank immediately, all sank 2+ hrs
good choice for very small particles
Most of the dust from this material was particles that were just smaller than the screen


This is super cool (coughI’m a nerdcough). Interesting to see just how small the Napa particles are compared to the other two. Perhaps I’ll give a batch of the Diatomite Rock a shot. What kind of DE were you using @MartyWeiser?

Oh, I also realized that because I’m watering a pond basket there are no side walls to allow the water to saturate the 100% DE substrate from the bottom up. I’ll experiment next year with 100% DE in a small pot and more maple saplings that I’ll inevitably find around the yard next year.

I’ve been using the O’Reilly’s Floor Dry with the dust (-16 mesh) screened out. I just started with it last year and the biggest use was in about 20 grow bags mixed 50/50 with the native topsoil which had been augmented with compost a couple of times. The goal of that is to encourage a roots system with better ramification where the vast majority of the native soil can easily be removed when I pot them up. I also up-potted a couple of seedlings in a mix where I replaced the Akadama in my typical 1:1:1 Akadama:pumice:lava mix.

The trees in the grow bags are doing well considering how much root cutback I did since most were in the ground already. However, it will be another couple of years before I can report on how well it held up. I live outside Spokane, WA so we get fairly dry summers and I was watering those every other day along with a fair bit of freeze-thaw in late fall, early spring, and sometimes even mid-winter.

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I’ve had these rubrum maple in 100% diatomaceous earth since last summer. I decided that I’d try to fuse three of them by inserting them into hole drilled out of a tile. When I worked them out of the DE I was surprised at the root growth. If you zoom in on the pic you can see a good example of the roots. A lot are under the tile.

I didn’t like the consistency of the DE though, so I replaced with a mix of pumice, de, akadama and pine bark.


Oh man, Ryan just asked Dennis about this technique. Stoked to hear that it works well…for Dennis at least lol.

If the tile is glazed, I like to turn it upside down so the new roots have the porous side to contact. I wonder if it makes a difference?

Ah, good idea. Luckily this tile has a matte finish.