Barreca Vineyards

Barreca Vineyards

From Vine to Wine since 1986

Sawdust to Soil

As I was driving down Webley road to the lumber mill, I remembered my last visit there 35 years ago. I needed to have some 1 x 4 boards planed down to ½” from ¾“ so I could bend them into arches for my first underground arch building.  That old mill was the only place nearby that did that kind of custom work.  The new mill is much bigger with huge logs sitting in the log deck and along the way in many stacks of sawn lumber, some looking to be very old, sticker-stacked for air drying. 

The mill was at the end of the road and I was at the end of my rope.  My new little biochar business needs lots of scrap wood.  Having used mine up, I got permission to cut up the slash piles of a couple friends.  But the wood there was still wet inside.  It would take dry wood to get it burning and would burn slowly with a lot of smoke. Still there would be a good chance of it not turning completely into charcoal. I was thinking I might find some long dry slabs with bark on at Webley Lumber that I could cut into burnable pieces.

I pulled up to the little log cabin office and inside found some very helpful people. They actually knew what biochar is and had used it.  They also pointed me to piles of dry mill ends, clean, already in smaller pieces and FREE for the taking.  I drove home intent on bringing my pickup truck back the next day and loading up. 

During the night I started thinking about something else at Webley Lumber, huge piles of sawdust.  It’s not good for biochar. But so much carbon!  As a carbon farmer intent on getting as much soil-enriching rotten wood back into the ground as possible, I couldn’t get it off my mind.  After loading up the next day I stopped to chat with a guy walking near the office to ask him about the sawdust.  He was Brent Webley, the owner/manager of the mill.  Milling lumber has been his family’s business for generations.

Loading up at Webley’s

It turns out that I am not the only person who noticed the sawdust piles.  Farmers come and load it up for bedding.  Others come and lay it down around blueberry plants.  In fact a blueberry farm near Reardon gets chipper truck loads full and plants berry bushes right into it.  This is not a really good idea generally speaking but they were loading up from a pile that is 30 years old, 80 feet high and bigger than 2 football fields.  Brent will load a pickup truck for $10, a super good deal.  I was eager to get some of this old sawdust and to learn more from Brent.

Brent caught me up on a little mill history.  His grandfather had a lumber mill in Orient.  His father, Buzz, and an uncle built their first mill a little closer to the start of Webley road which comes off the far side of Gold Hill Loop just west of Colville.  In the 60s and 70s they built newer mills on the current site.  There was a big fire in 2001 but the mill itself did not burn.  I asked him if all of his business is local.  As it turns out, only about half is. Webley regularly ships lumber to Spokane.  Additionally, one of their specialty products is custom shaped logs that can be stacked into log cabins, such as their office.  To do that they need already dry wood that won’t warp or crack.  So they have large bundles of big poles aging on a hillside before they are dry enough to use.  These cabin logs are shipped all over the west and as far away as Japan.  Old sawdust is just a minor income source.

Fresh sawdust is not a balanced soil amendment.  It is acidic.  While breaking down it draws nitrogen from nearby vegetation as well as water.  If you put new sawdust right on your garden, it will pretty-much kill everything.  Biochar is a little like that too.  It will suck up water and does not have any natural nutrients.  Both of these soil amendments have huge amounts of carbon, the main building block of all biological life.  The sawdust can only release its carbon as a nutrient after being digested by microbes.  The biochar doesn’t ever break down but preserves moisture and millions of beneficial microbes which, among other things, can help break down sawdust.

So let’s “break that down” a little more.  There are two main avenues to getting microbes to digest sawdust.  One is to get fungi growing in it.  Fungi are much better at digesting wood than bacteria.  They need water, air and a good source of already living fungi.  Mature compost will usually kick start the process, or even old leaf litter from the forest floor.

What fungi don’t need so much is to be regularly turned over and mixed.  That breaks up the mycelia, the thin threads of fungi that transport water and other nutrients.  You want the mycelia to spread through the sawdust.  Eventually you want them to form a symbiotic tie to living plant roots.   They get sugar from the plants and bring water and minerals in exchange, effectively spreading the reach of the roots by orders of magnitude.  I mix shredded woody material with finished compost, aged manure, rotting fruit pulp and microbe-enriched biochar and spread it under my grape plants to let it mature in place as it would in nature.  (Come to think of it, I’m probably maturing in place myself.)

Meanwhile, remember those farmers that use sawdust and wood chips for bedding?  That is another great way to offset rotting wood’s thirst for nitrogen by getting urine, manure and moisture mixed into the sawdust so it can be digested by microbes quickly.  Animals get the nitrogen in their urine from eating green leaves and grass.  Chlorophyll in green vegetation creates sugars from sunlight.  After going through a digestive system or even just being mixed in fresh with dry plant matter chlorophyll releases nitrogen that bacteria and fungi trade back and forth to create rich organic soil.  One part green vegetation to 3 parts brown is a standard ratio to have in compost.

The key to knowing if it is working is worms.  Worms can eat leafy matter and food waste early in the composting cycle.  But old sawdust that has rotted sufficiently gives worms a long-lasting food supply.  My compost and aged manure piles are full of worms.  There is a lot more to say about them, but let’s stick to sawdust for now.

After I had my truck loaded with two big scoops of damp red sawdust I started back toward home.  As I got onto pavement and speeded up, the sawdust started to blow around.  Out on the highway I was leaving a thin red cloud in my wake and slowing down a few cars in the process.  As soon as possible, I stopped to buy a small tarp and cover the load.  Take my advice and bring a tarp with you if you go to Webley Lumber for sawdust, but by all means go.  Get that carbon into the ground.

4 Responses to Sawdust to Soil

  1. Synchronicity- Roger is going to a local sawmill this week for scraps.

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    • Glad to hear that. Both the mill ends and the sawdust have been very helpful this Spring.

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  2. The miller wants me to take a load of sawdust as well. I’ve been reading about torrefaction, a lower temperature process than pyrolysis. Torrefied sawdust can be used to make pellets and potting soil.
    Keep up the good work, Joe!

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    • Okay. I had to look up torrefaction. (https://www.etipbioenergy.eu/images/EIBI-4-torrefaction%20and%20pyrolysis.pdf) It is the heating of wood at low temperatures to drive off moisture in the absence of oxygen so that it does not catch fire. As Roger points out, it is useful for some things. It does not create the openings that absorb moisture as seen in biochar. So it reduces the transport cost of wood-sourced fuel and contains more resins that can be digested by microbes. So it doe not last hundreds of years in the soil like biochar. As I point out to folks, the best effect of carbon sequestration by biochar is that it promotes healthy carbon-rich soil, which in the end is sequestering more carbon than just the essentially light weight biochar.

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