Sawdust or Bark Sheet Mulch

So I was looking at a copy of Ruth Stout's No Work Gardening book. In the book at some point Ruth suggested that not just hay or straw would work for her style of sheet mulching, but also sawdust.

This proposal intrigues me because I can get a huge load of sawdust delivered easily- in fact have done so in the past.

The last time I got a big load of sawdust was I think the spring of 2016. I tried to use it only on the paths, but somewhat inevitably got some into the beds, and have had some resulting poor performance.

However, in 2017 I tried to grow corn in a much older base of a bark pile. The bark pile has to date back to at least 2012. The corn was actually half in bark pile base and half in sand pile base. The corn in the sand pile base did great, and the corn in the bark pile base did poorly.

So in 2018 I planted my fava bean grex into the bark pile base and they did great. I also put fava bean grex into the sawdust pile base from 2016.

So this is my thought.

Try using a sawdust and or bark based Ruth Stout style sheet mulch, but modify it a little. Plant legumes the first year after initial application. I know fava beans will probably continue to work, but could also try beans, peas, garbanzos, lentils, fenugreek, and other legumes.

With the Ruth Stout method part of how it works is by doubling down on spreading more mulch year after year. Also not tilling the mulch deeper into the soil- something I tend to do a bit.

Another great modification would be rather than using legumes for a year, would be to use chickens as in a modified chicken tractor methodology. For instance the bark or sawdust could be spread in the fall, then chickens penned in the garden over the winter, then in the spring the garden planted normally.

So in this scenario, surface area is king. The more surface area your decomposing mulch has, the more room there is for native soil bacteria to occupy.

So the finer the material, the more surface area, and the more seats at the dinner table for soil life at any one time. Thus, the larger and more significant the soil life and nitrogen draw-down to colonise and break it down.

So the finer the wood product that you're using, the more nitrogen it will need.

I normally just pitch my coffee grounds into my compost bin, which is more of a ground-connected vermiculture bin at this point, owing to raw paper-based rabbit bedding, but when I introduce large amounts of wood chips as mulch in garden beds, I will add my daily grounds to the mulch, and I will actively seek to gather grounds from those around me that don't compost, or from coffee shops.

Compost-inoculated biochar would be a great addition, as would compost with lots of biochar in it. That would significantly reduce the soil life draw-down, as they would already have colonised the biochar; you'll be importing exactly what that kind of biomass addition would remove from the soil.

I think that the nitrogen-fixing bacteria host green manures will do well, but they will do better if you take steps to introduce more soil life to the mulched area first. In addition to the suggestion above, one could instead, or also, brew up an oxygenated compost extract and inoculate the chips or sawdust with that. Also on the table are mushroom slurries, either culinary or wild inedible. Some research into specifics might help, but if you get fungi that prefer a woody substrate, they will colonise the woody material and be of great benefit to anything trying to grow.

But let us know how it goes, and good luck.

-CK

I recommend against using sawdust as mulch in planting areas because it tends to mat down and repel water.  But great for paths.  I'd add it to a compost heap with lots of nitrogen materials if I wanted to use it in planting areas.  Just don't use a solid layer of it because of the matting problem.

I do the same as Tyler.  I can get large amounts for free but I use it for paths.  It will eventually become soil, but since it is in the paths, the longer it takes to break down, the better.  I would be hesitant to use it in beds for the reasons already given.  If you want to try an interesting experiment, make a mound of sawdust and flatten the top.  Water it or wait for a heavy rain, and afterward, go out and dig into the sawdust and see how far you can dig in before the sawdust is bone dry.

I would probably use sawdust if I had a need for a lot of brown to offset a lot of green in a hot compost. The finer the material, the more surface area, and the more homogeneous the mixture, leading to a lot of edge habitat for the thermophilic bacteria.

I would expect sawdust in the right conditions would make an excellent gley layer, a great thing if you're digging a pond; not so much if you're trying to grow things.

-CK

One thought I have in terms of proceeding cautiously would be to replenish the almost decomposed sawdust in my paths. Then do one bed surface as an experiment and definitely have that be a bed of legumes next year.

Another thought might be to start a bed with hay as Ruth Stout did. Then in a subsequent year once a decomposition gradient had already been established, do a fresh layer of sawdust.

I haven't noticed the local pine sawdust matting. Wonder if your local sawdust is a different type?

Thicker leftover sawdust piles last a very long time in my climate. I've definitely noticed that in a thick layer the water doesn't penetrate far.

I would like to play with biochar more. Thinking about getting something called a "biocharlie" for the fireplace.

I would also like to play with sheet composting more. We used to always use bagged grass clippings as garden mulch and compost pile fodder.  Then we switched to mulching mowers. I'm thinking about getting an small electric bagging mower just to harvest mulch.

Wonder if bark would be better. It's in larger pieces so decomposes even slower. Has a much darker albedo. I get it from the same place as I get sawdust.

Turning the sawdust into biochar 1st sounds like a wonderful idea. I love it alot.

Other than that I would compost it, then add it to the path garden bed.

Also worms, birds and other lifeforms will move yoour sawdust around.

I bought a 3 lb bag of omri listed blood meal on sale at Walmart the other day. Realized today it was a very good deal. I will buy more if they still have some next time.

Blood meal is something like NPK 12 0 0

Wonder how much sawdust or bark you can mix with blood meal to get the optimal C:N ratio of a compost pile?

I think part of how a deep mulch system works is that the soil is a N source but only gets depmeted by the C in the mulch in a certain layer.

Sawdust and bark are a much denser source of C than hay or straw.

Fresh green grass is a good source of N

We used to stockpile leaves in the fall to mox with grass clippings.

Ideally N should be below C in a mulch layer.

I never bought Pat Lanza's book on lasagna gardening because I had already read a couple earlier articles by her on the subject. Basically as I recall she makes kind of a sheet mulch compost pile. Usually with a sterile soil or potting soil type mix on top so it can be immediately planted into. I see it as part of a mulch gardening continuum with Ruth Stout gardening, chicken tractoring, and hay bale gardening.

Also I have some older partially composted sawdust leftover that needs spread. I may try that on a bed surface.

Sawdust and bark are cheap here but not free. I have tons of grass- if I can harvest it easily it is free.

I had cool mushrooms in my garden recently from the sawdust in the paths.

That biocharlie device is cool,  and so easy to DIY!
A youtuber who shares his work here showed how he uses stainless steel steamtable pans to make biochar in his woodstove, saving on firewood at the same time.
Sawdust should be perfect for biochar,  to the point that building a 5 gallon TLUD for the fireplace or a dryer drum sized TLUD for outside would be worth while.

How about pee as the nitrogen source to balance the carbon in sawdust?
It's free!

Sawdust is between 100:1 and 500:1 C to N ratio (nitrogen here is probably related to freshness of sawdust).
Blood meal is 3:1 C to N.

.: between '3 parts blood meal to 1 part sawdust' and '16 parts blood meal to 1 part sawdust' to get your C:N around 30:1

It would make a lot more sense to just use green grass clippings. (5:1 to 15:1 carbon to nitrogen)

My favorite use for sawdust is to evenly mix with leaves, twigs and grass-clippings around fruit trees.