Reusing soil after repot?

After a repot of a tree that was in modern soil, what do people do with the pumice/lava that came out of the container? Unlike the akadama which will have broken, these should be by and large intact, right? Do you sift it and wash for a future use, or chuck it?

I routinely reuse my soil, including the akadama. Just let it completely dry out and then screen it to get rid of any broken down particles. You’ll have to eyeball it prior to use and add fresh components to adjust the proportions of akadama, pumice and lava back to 1:1:1, or whatever proportions you are using.

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Ryan said that he re-uses his soil if it hasn’t broken down too much.

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I recycle APL every year. I screen, wash and dry old soil and then add about 25% akadama back to the old APL mix. I think it is pretty common practice.
I also use it, sometimes unwashed and un-screened for lesser material in development. Stuff in ground on tiles, or in grow bags. I mix the old bonsai soil with native yard dirt.

I also reuse, but don’t wash, and like to dry it in the nice hot sun in a thin layer on a dark tarp to partially sterilize it.


I usually put my used APL, after sifting, in an aluminum pan (the tin foil type) and put it on the gas grill and bake it for a half hour at 400F or so to ensure it’s sterilized.


Be careful with those high temps when sterilizing your soils. :grimacing:
Overheating your soils can begin a chemical reaction that will release a chemical that is harmful to your trees. Not sure what chemical, I have not gone too far down that rabbit hole yet. :+1:t2:
Lots of info online, good and bad.


Ok… good thing to beware of. I haven’t noticed any negative effects on trees using reused sterilized soil yet. But I will keep my eye on them. I don’t do it often, but 2 or 3 times during repotting (out of 30+ trees last year).

I did a google search on soil sterilization and found the webpage below which seems to be fairly good. I did not do a deep dive into the background literature. The quick summary of the page is that temperatures of 180F (82C) for the center of the soil will kill most pathogens and leave at least some of the beneficial fungi and bacteria. Temperatures much above 212F (100C) can result in the formation of toxins (not specified). Solarization is listed as preferred for larger quantities of the ground. Moist soil is easier to get to a uniform temperature (water conducts the heat).

Soil Sterilization Techniques, Ideas, Tips | Agri Farming