Heat bed meduim? Pumice or bark " sawdust"

Was curious if anyone could clarify.

@Ira I know Ryan uses and talks about pumice as the heat conductive material at the bottom of heat beds ( depth being the key variable).

But when Ryan and Randy discuss about post collection Yamadori recovery Randy explains that for a single year and for trees that require rapid root growth, he has seen bark " sawdust" give superior results.

Why would you not utilize this at the bottom of a heat/recovery bed? Is the nuance dependant on the trees roots being directly in the meduim ( sawdust/pumice) vs in a pot in the meduim?

Warning: If anyone has not listen to this, please do NOT mistake this for regular sawdust! My intentions were not to confuse.

That would be my guess. the irregular shape and size of wood makes for good contact with structures like roots, but less contact for a ceramic pot. Pumice being smaller and more uniform would make better contact with pot walls.

Heat beds are also kept warm and wet so wood will break down pretty quickly and pumice wont.

Still, its an interesting idea. It seems like using coarse sawdust would work at least close to as well as pumice.

Thanks for sharing your perspective, much appreciated!

I went the route of saw dust in a raised recovery heat bed because of the cost deferential. I will share the results when winter in the Northeast has passed.

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Cool setup. What are you using for heat?

I have an iPower (Amazon link below) heat mat. Double insulated under and waterproof liner ( construction plastic) over that mat


Amazon.com : iPower GLHTMTM-A 20" x 20" Waterproof Durable Seedling Heat Mat…

Thanks. I’ll check it out.

Nice. Good luck and let us see how it goes!

Just an observation, I think the materials used as a heat conductor can be varied based on what is readily available in your geographical area! I’ve heard of course sand, course sawdust, pumice, fine lava rock ect all being successfully used.
I built mine and have used medium grade perlite as my heat conductor with good success, the trick I’ve found is keeping the material moist which is what allows the heat to be spread evenly. I’m also using hot water as my heat source which is in a recirculating loop.

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Are you sure they talk about bark sawdust? To my recollection the medium was coarse sawdust (or closer to woodchips). I would not know how to produce sawdust made from bark (i can purchase for example pine bark, which comes in smaller partiales but not saw dust from bark).
It is what to my understanding Randy‘s heatbed is constructed of where he directly plants into.

I use the Aspen bedding for hamsters or small rodents caging based Randy’s recommendation … It’s more like wood shavings it your familiar with hand planing wood.

Since I have started repotting some stuff already this year. I can say everything that was recovering or growing in 80% or higher with this meduim had twice the root production ( large amount on fine feeder roots) when compared to a 50% 1/4 perlite, 25% compost and 25% (wood shavings/ pet bedding).

Randy mentioned that this the number 1 way to do it for a year or maybe 2. He didnt go into details but I am assuming ( and could be wrong) the duration is the variable of what makes pumice superior, especially when operating at scale.

But my scale is smaller so I’m trying 1 year in the ( bark/bedding) then see what makes the most sense based on the roots and trees response.

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