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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Some changes after year one. Went with 1/2 inch drainage layer 2 inch thick of perilite(pumice is not affordable in the north east). Added about 10 drainage holes and went with shaved Aspen bedding ( corse saw dust) sifted out all the fines on everything. It was staying too wet last year and I also added wheels so it can be easily moved.

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Great looking heat bed!

I was wondering have you ever collected yamadori in the fall and put them in this type of heat bed for the fall to improve root growth before winter? or overwintered in heat bed?

Also if you don’t mind saying. I was curious how much using one of these heating pads increases your electricity bill?

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I do and it was the main reason I built it. 2 green ash I just got last week ( unexpectedly) while doing a garden wall renovation!

Also I have had much better luck collecting Fagus Grandifolia (Beech) in the fall at leaf drop vs. Spring pre leaf push ( horticulturally it makes no sense in theory but is what it is)

Here they are before I fixed the heat bed. I took them out of the boxes and placed them directly in the heat bed.

As for the cost of running hard to say because I also bring in my focus, succulents, cactus and pitcher plants at this time and start using my indoor grow lights. Including the 3 indoor lights and outdoor heat bed I see the electric bill go up $20-30 a month from now until March.

So maybe $10-15 a month to run the heat bed. It’s double insulated and last year I laid black 1mil construction plastic over the top when the heavy fall rains and ice came.

I will probably end up walling off the sides essentially making it like the “black bag method” used for collecting oaks or weak yamadori.

I figured I would share thile main things I use it for. I don’t have a green house so stuff that’s in pond baskets over the winter ( some go in the ground),recently removed airlayers, spring repotting ( I put the container in there until I am clear of frost in my zone plus anything I made a mistake on or lacked patience as I am still a newbie.

It’s not a substitute for doing stuff at the right time of year but some of us learn by touching the hot stove… several times!

All in all it was well worth the time to build it especially living in the northeast.

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Thanks for the info!