Have you had any luck with DE since this post??
I just dug up 5 of the trees I potted in grow bags using DE in that I planted in May 2019 using a 50/50 mix of garden soil and DE (I think the Napa Oil Dry based upon the particle size). The DE held up very well over two growing seasons and these were by far the best root systems I have seen from ground grown stock (including some I have purchased from good growers). Not sure if it was the particles or the DE, but I am sold.
4 were Acer tegmentosum (Manchurian striped bark maple) where it was easy to loosen the outer 1-2" of the 13" x 4" soil mass to fit into a nursery pot. They will be sold as garden trees at our club’s annual show and sale since they did not thicken much in that or the previous couple of years in the ground. Unless someone wants to make literati maples with leaves the size of your hand - they have good movement and the roots can be reduced!
The fifth was an Acer campestre (field maple) that was grown in a 19" wide by 5" deep grow bag. My experience with A. campestre is that they pick a couple of roots to grow explosively with limited growth of the others so it is difficult to develop a good nebari, particularly in the ground. This one had a bunch of strong circling roots around the outside of the bag, but also a wonderful set of fine roots close to the trunk - comparable to what I see for pre-bonsai maples grown in shallow pots in bonsai mix.
I removed about 90% of the soil from the 19" diameter by 5" thick root ball with a chopstick and washed the rest with a hose. After some additional root pruning similar to what I would do on a newly established maple, I potted it into an 18" x 12" x 2.75" box with a mesh bottom using a 4-1-1 Akadama, pumice, lava mix (I have yet to adopt solid Akadama with my watering scheme). It has a 3" trunk above the nebari and I hope someone jumps on it at the Inland Empire Bonsai Society Show and Sale in July. Pictures of the root ball from the ground, after washing, and a possible front attached.
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Thats awesome, the reason I’m nervous about using akadama and DE is because I live in Louisiana. It gets really wet here sometimes with a lot of rain. I have heard that akadama and DE can break down really fast here. What could I use for a replacement for akadama/DE so that my trees don’t suffer?
I don’t think I observed any real break down of the DE in the grow bags. They would have been continuously moist for two years with some freeze/thaw thrown in as well. I am guessing it would hold up well and give some needed cation exchange capacity. If you are concerned make sure you have some pumice and/or lava to help maintain the structure.
The nursery industry uses bark to get the CEC, plus it is cheap. However, I am not a fan of bark in a bonsai pot - it is a warm, moist environment in the summer so it will decompose fairly fast. I do use it to develop young stock along with pumice to help maintain structure. That makes it much easier to untangle the roots when repotting.
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So what brand of DE would you say is best. Im gong to try it out on some trees. And do you sift it to any size?
I think the major supplier of DE in the USA is EP Naturals/EP Minerals. Both the Napa and O’Reilly’s floor/oil dry I tested were from that source. My sieve analysis is towards the top of this thread. I would probably use the O’Reilly’s Floor since the particles are larger (61% between 4 and 8 mesh, 37% between 16 and 8 mesh). Before I used it, I would get a single bag and screen it to see the size (wear a mask). I did not wash it since it was going into grow bags, but in a bonsai pot I would do so after screening. Based upon @Bonsai_Bentley 's comments above my data, I would definitely combine with pumice or similar to keep from compacting and shedding water.
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This an old post and old topic but having recently repotted a few tropicals I’ll share my experience. I was surprised by the roots in the soil with DE. They looked robust at first removal from the pot, but after cleaning them out found that all roots were on the outside and circling the pot. Shin was empty. I also found the soil to be far more wet than I anticipated given the devastating heat of this Texas summer. The lower 2/3 was quite muddy, with other particles breaking down and the DE not.
My conclusion is that the DE does hold water well, but it does not give it back to the other particles or the plant. I aslo found no evidence of roots penetrating the particle like you see in acadadama and sometimes porus shale or pumice.
I will not use or recommend its use going forward.
I see Marty’s example above when combined with garden soil for feild growth and can see its benefit, no so much in a pot IMO.
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Thank you for the review Moon! It’s interesting to hear your conclusions and DE holding water and not releasing it, makes sense as that’s what it’s designed use is. But of a bummer this is how it played out.
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Thanks for running the experiment and sharing the information!
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