Concerning sawdust

I'm building a raised bed out of standard 8x8x16 hollow core cinderblocks. Most veggie's roots do fine in less than 24" of 'soil'.  So I'm thinking about filling the bed up 1 or 1 1/2 blocks high with sawdust from a mill that I know uses untreated hardwood. Can anyone tell me if this is a good idea for a "filler".  I know its not Hugelkultur, but will it work?

Thanks in advance for your responses!

PS. Keep up the cool vids on YouTube, Paul. LOVE THEM!

What I forgot to mention is that I'm going to be using the sawdust as a filler for the first row of blocks, and top it off with my usual mixture of compost and vermicompost. I heard in one of Paul's vids that in Hugelkultur that the first year the trees were "taking" more nutrients away from the soil, but later returned it. What I'm wondering is will sawdust do the same thing to my top 8-12" of compost? Also, is this going to throw off my pH levels drastically?  Thank you guys, y'all are the best!

You might want to compost it a bit first else, in my experience, not much will want to grow in it.  I get loads of sawdust from a nearby mill and I find that mixing it with donkey poop and adding urine to it helps get it going nicely, but it does take quite a while before anything other than beans will grow in it. 

Am I correct in thinking that you will have several inches of soil on top of the sawdust?  I didn't read as to how tall your beds are going to be.  Other than maybe being kind of on the 'acid' side, I bet you could pull it off, maybe not with the best results in the first year.  I agree with Burra, if you can compost it first, it'd be better.  But for me, half the fun of gardening is 'I wonder if this will work'. 

Out of desperation, I used plastic milk jugs, big styrafoam chunks, etc for filler in a 3 course tall concrete block 'thing' that was already here when we bought the place.  I dumped what little compost I had managed to get on top of that, watered it down, and the next day planted flowers.  Sure settled fast but it bought me the time I needed.  Now I pick out whatever is creeping to the top and adding more soil, kitchen scraps, etc to the bed.

I have two other concrete troughs that I filled with all kinds of dry yard debris and straw, and then put compost and soil on top and planted sedum (really short root system).  It grew fine, and again, is settling fast.  But it bought me time again to get something composted.

i'm eager to hear peoples thoughts on this as well.

i end up with lots of pure clean sawdust and shavings from my woodworking/woodturning projects, i can also get free "waste" trees/branches and freshly cut woodchips dropped off by local tree services at will. i've used the chips for garden paths and as mulch around bushes etc, didnt seem to hurt anything,not sure how to measure nitrate leaching.
 
i want to make more beds for this spring.maybe making them now/soon and filling with woodchips will be enough time for some composting? maybe mixing in some kitchen scraps and juice-pulp from the health store .

My Dad used wood chips from a local tree man.  His soil was awful,  solid clay that had trouble growing grass when he started his garden there.  He did compost the chips for at least a year befor using them though.  I currently have a large pile of wood chips composting since last spring,  I plan on using them around my apple trees this spring.  Last fall I was able to get some horse manure from a friend.  It turns out he only has 1 horse.  He really loves that horse,  so he changes the bedding  [  saw dust from a lumber mill  ]  very often.  So most of the 2 small PU truck loads that I hauled home were mainly saw dust.  I double dug a 10' X 10' area of the garden and put that stuff on the bottom to act as a sponge.  This is the 1st time that I tried the horse poop,  I plan on tomatoes in that section next year.  I have been double digging a diff section of the garden and putting a heavy layer of leaves on the bottom for several years with Great results.  Mt tomatoes were over 6' tall last year and produced very well.  I dont know if the saw dust and horse poop will work better of worce than the leaves.  We will know next summer.

yeah, the use of large amounts of carbon materials, woody stuff, in garden beds makes me wonder to.

when first hearing about hugelkultur beds the thing that popped in mind was so where do you get your nitrogen from. Then asking experienced gardeners about using woody materials they declared it a big no-no (at least in veggie beds or kitchen garden, when growing blueberries or other vacciniums its fine). because in order to decompose (aerobically) the wood would take already present nitrogens from the soil and thus competing with your plants...

So when i asked a permie teacher here he said that as a mulch woody materials give these problems, but when using wood in hugelbeds this is safe because it is dug into the ground quite deep, he didnt go deeper into it than that because something else came up.

Later i started to wonder, how deep do you need to dig it in then, and does that mean that in hugelkultur beds the wood is decomposing anaerobically (thus not needing ANY nitrogen), or just much slower?

but thats a question for another thread.

for filling the beds with sawdust it matters wether it is a different composting-proces or just the speed it decomposes in that makes a hugel bed not have nitrogen deficiencies.

If it is about how fast it decomposes at depth, using sawdust in stead of whole logs could speed it up, and then mixing it up with dung, urine or other N sources might be wise.

Rotting wood (chips or sawdust) will use all the Nitrogen it can get, leaving little or none for the plants.  This is a good thing for a mulch on top of the soil, but bad if mixed in or too thick.  Burry a layer of it, and it may well still be there a decade from now, and still pretty much lifeless.

I've used it in the past for hilling up spuds and by the next year it was fairly rotted.

Bloodmeal does wonders for making it rot in a hurry.  So will MiracleGro if you are willing to give a one-shot does of something not organic.

Will urine/water make it break down faster, too?  I'm still pondering this whizzing on the compost thing.....

Sawdust is a very nice clean way for the paths. And there it composts and you only rake it into the beds.

Marianne wrote:
Will urine/water make it break down faster, too?  I'm still pondering this whizzing on the compost thing.....

Yes it does! 

I was so short of compost that when I first managed to get hold of a load of sawdust I tried just keeping it damp and (please forgive me guys) adding a sulphate of ammonia as I'd been told that a high nitrogen fertiliser would help it break down. Maybe a more complete fertiliser would have been ok, but my initial experiments just yielded damp-looking sawdust after about two months of 'composting'.  Ditching the fertiliser and using urine instead made a huge difference, both in the pile I already had composting and in new piles.  But the greatest difference happened when I would build the heap a bit slower and add a layer of donkey poop every time I had enough, then another layer of sawdust, then more poop, and add whatever urine I could collect along the way. 

It's still a fairly slow process though, much slower than 'normal' compost, but it does get there in the end.  I ended up with a row of six compost compounds in the hope that I'd always have one ready for use but never run out of space to add more 'stuff' to my heaps. 

Burra,
so you didn't add a green layer in your piles?  I always have access to straw, can get cow manure, but green stuff is more difficult for me to get.  It's always full of wild grass seed after we mow.  I know the urine is supplying the nitrogen, so that's taking the place of the green layer in the composting? 
I have a small pile going, but most of the time, everything is added to the garden as I get it, including our pine sawdust.  Oops.  I didn't know about it leaching out the nitrogen.

The best/fastest piles had a layer of donkey poop, which is a green, albeit a pretty mild one as the donkey is fed on straw.  'Green', in composting terms, is a measure of the nitrogen content as compared to the carbon it supplies. 

If you have a supply of cow manure, then that would be an excellent green!  Just layer manure and sawdust until the heap is full and then water the heap with urine. 

If the sawdust you put on the garden is just used as mulch then it isn't going to rob the nitrogen very much - it's only when you try growing the the stuff before it's composted down that nothing but beans will grow in it. 

When I'm *really* organised, and have a bit more time to spend at the farm, I like to keep the donkey on a nice thick bed of sawdust and then clean her out very thoroughly every day, 'wasting' lots of the sawdust bed - that way I don't need to worry about layers in the heap as she mixes it all up for me, which is even better than layers.  But these days I don't get a chance to do that so I have to improvise a bit. 

I don't have the cattle, but there are farmers out here that have cows, so I just have to make a phone call.
Yes, I use the straw as mulch in the garden, and have grown potatoes in straw, too.  I used to let my 8 hens in there first thing in the spring, and then after the harvest for a few months..  Not enough hot chicken poo to damage anything, and they did a pretty good job of tilling and breaking down the straw into smaller pieces.  They don't give a hoot about the wild grass seed that blows in, dang it.  Anyway, maybe the chicken poo was making up for the lack of nitrogen that was there.
I pile the chicken litter and let it age for a year before I use it in the garden, but it's mostly straw, too.  Unfortunately I'm down to just two hens now, and one of the young barn cats thinks it's great fun to chase the hens, so they're kept in the run. 
We're going to do the urine/ water thing when the weather warms up.  We just got 5" of snow last night...brrrrrr.  But with all that straw (AND the sprinkled sawdust!), I bet I'm going to have a serious nitrogen deficiency this next year unless I do something pronto!

i love using sawdust as a mulch ..it makes a wonderful mulch..

I don't see any reason it would not work well to be buried either..make sure you are getting enough nitrogen type products

There seems to be alot of interest in this topic.  With some of the comments I am getting a little bit concerned about what I did last fall in my garden.  I burried saw dust bedding with horse poop about 3' down in the garden thinking it would act as a sponge and hold water.  I put it in about 1' deep.  Some of it was a bit rotted,  but some was pretty fresh.  I was not worried about weed seeds because I put it so far down.  My plan is to plant tomatos in that spot this spring.  They put down roots atleast 3' so I feel their roots will hit that layer.  I have buit up my top soil over the years to about 15 to 16 inchs and I layed the sub soil with leaves as I back filled the hole.  I have been doing this process in other parts of my garden for some years but have always just used the leaves and not saw dust.  I have had Great results so far.  I am wondering if the saw dust will work as well as the rotting leaves have worked in the past.  Since it was horse beding it did have the horse pee and poop mixed in with it,  I guess I will just have to wait and see at this point since its already done.  Next Aug. I will know for sure  I guess.  We all make mistakes,  because of all the work I do I am hoping that this isnt one of them. 

What I'd worry most about with sawdust is drainage and aeration. I think a solid layer of sawdust could easily impede the movement of air and water through the soil. Like the concerns about nitrogen, this can be fixed by mixing the sawdust with soil, straw, green manure, poop, and pee.

My grandfather used to make hot-beds for early tomatoes where they would dig a trench, fill it with horse manure, then replace a soil layer and transplant early tomatoes that would benefit from the warmth generated by the intense biological activity from the manure over the short term, and nutrients over the long term -- so I think there is subtlety to the practice and the devil may be in the details... do report back on plant growth.

saw dust has a high carbon to nitrogen level (C:N) meaning that in sawdust the amount of carbon is significantly higher than the amount of nitrogen.

decomposition is carried out by microorganisms and they need nitrogen to complete the process so if you use something like sawdust which has a high C:N ratio then the microorganisms will take the nitrogen from the soil or in your case your compost in order for them to decompose the sawdust.

you have to have a source of nitrogen for the microorganisms to decompose the sawdust or else you will probably only have luck with beans or other legumes.

i recommend composting the sawdust first and using urine or another source of nitrogen to really get it going.

in the future try using something that has a lower C:N ratio if you want to plant directly into it

Back in the 70s, the garden guru Jacob Mittleider actually recommended growing plants in a 50/50 mix of sawdust and sand, then adding fertilizer. Reported results were excellent.

Though I don't use much in the way of chemical fertilizers, I did find this quite intriguing. Being short on soil for one of my 4 x 16 raised beds, I added in about 1/3 sawdust, along with some biochar, sifted sand from my chicken run (here in FL, we have LOTS of sand), a bit of peat, some vermiculite, some potting soil and whatever else I had around. I then dumped a few gallons of urine all over it, then planted that sucker.

Everything is doing fine. I'm going to attempt higher levels of sawdust and see what happens - but I can tell you one thing: if your soil is dead, barren, sandy, etc - urine will grow you some amazing plants.

I used uncomposted stable sweepings when planting my asparagus this year and they grew well. Hard to say the ratio but it was probably something like 3/4 wood shavings with 1/4 shit/piss.

I skimmed through the other replies and didn't see this so I hope my info isn't a repeat.

My father did a Mittleider garden back in the 70's (I still have the manual). Once the sawdust had composted, he treated it like regular garden soil. He was a soil microbiology, so I guess he felt qualified to make adjustments as he saw fit. He did admit there was a trade-off in not using the recommended quantities of fertilizer, but we weren't trying to make a living at gardening and fertilizer was expensive.

I have an abundant source of human pee and sawmill dust, so I want to compost them together, but I don't know the ideal ratio, conditions and timing. Any tips?
One thing I'm particularly concerned about is leaching into the soil. How can I contain any leaching?

Just from my own personal experience, you are probably going to need more nitrogen than what's found in urine saturated sawdust. Sawdust has a crazy high carbon to nitrogen ratio (300-something parts carbon to 1 part nitrogen I believe). Bacteria will use up the urine in the pile and you'll be left with quite a bit of sawdust leftover.

Actually, now I'm curious. Is urine leaching actually a environmental hazard? Obviously, it would depend on how much you're dealing with, but still....

I was going to start a new thread but this one is good enough. I want to use sawdust as mulch before it turns to compost because I don't want to wait a year or two, but I also don't want any trouble.

It all started when I needed a place to store my pee until spring. I was diluting it and pouring it little by little over my six acres of orchard grass/alfalfa field, setting up flags so I knew where the next batch should go. Then winter came and I didn't want to walk out there in the cold and snow. What can be better than sawdust? So I got the bright idea of setting up a 30 gallon black trash can right outside my front door on the porch. Talk about convenience! I empty the carved out gallon water jug with handle intact several times per day. The remnant gets diluted (rinsed) with a little water for all the houseplants. Everybody is very happy here, plants especially. No bad smells anywhere.

I put a whole bag of hardwood sawdust pellets in the trash barrel. It takes about 15 days worth to soak up all those pellets turning them into sawdust. It looks like I will be able to fill up five more trash cans by April. Then I will have other uses for this precious fertilizer. Precious because I live alone and only have so much.

I didn't know of anyone doing what I was doing so I inquired of Mr. Google. I came up the most inspiring, right up my alley article called "Sawdust is My Slave."

http://us.naturespath.com/blog/2009/07/10/sawdust-my-slave

This guy put sawdust around all his trees and berries and knew better than to mix it in and he got away with it. He doesn't say anything about aging or composting it first. I am a little shy about putting on fresh sawdust but at least my sawdust is soaked with urine. I was a bit concerned about there still not being enough nitrogen in there for mulch for my plants.

I had another talk with Mr. Google. He showed me an article telling how much nitrogen to add to 50# of sawdust before using it for mulch so it won't rob the plants. Bingo! They want 1# of nitrogen per 50# of sawdust. Further research told me there is between 4 and 10 grams of nitrogen per litre of human urine. From using the hardwood pellets for making mushroom substrate, another hobby I started this winter, I know by experience that it takes 25 litres of water to soak up 50# of pellets. Doing the math I find that there is at most 1/2 pound of nitrogen from my pee for every 50#of sawdust. Half of what I need. I am going for it because that is the best I can do. I mulched my strawberries last week during a warm spell. I have a lot of strawberry plants still in pots I propagated last summer. In case something goes wrong, I have back up strawberry plants.

I might also try making compost with it, Berkley style, layering it with nanny berries. I have 40 goats so my supply never ends. It is a lot of work turning those piles. I would rather use it for mulch. Less work.

Has anyone here ever used urine soaked sawdust for mulch? And were your plants beautiful? Marilyn

I became interested in saw dust this past winter as I just didn't want it wasted...I bring home logs and chainsaw them on a concrete slab then sweep up the sawdust by-product which goes into a 44gal drum till needed.What I do is half fill a bathtub with sawdust then all my chicken manure I fill it up and throw in about 60lts of rainwater...mix it all up and let sit for about 3 mths turning it every other day as it dries out on top.I wouldn't know the science behind what I do but it sure works for my beds as when ready to start transplanting seedlings I just till the sawdust through with compost and this year I've had vigorous growth bumper crops.

I just spent the last 4 years mulching my garden with sawdust and everything has been growing well. Increasingly well as time went on and the sawdust got incorporated into the soil to break up the clay.

2 yrs. ago i planted 30 various berry bushes. i sprinkled a half in thick circle of worm castings around each plant then put 3in. of green hardwood sawdust as a mulch. they all took off! last spring i pulled back the sawdust to put down more worm castings and about 2in. of the sawdust tuned into nice black soil. i returned the old sawdust back and dressed them with 2in. of green sawdust again. no weeds at all. other than watering, worm castings are all i give them and they're doing great! the sawdust is composting itself nicely around my bushes!

For what it's worth, a lot of greenhouse growers use sawdust as a substrate. They have to inject more N for the first few weeks, then taper off as the sawdust breaks down. The biggest issue other than N is drainage. As the sawdust breaks down, it compacts and becomes a bit like muck. Personally, I'd use it as toilet cover and chicken coop cover, but not to plant straight into. Bark/chips/branches break down much slower, and allow way better drainage. I would think free sawdust would be excellent mulch. Remember, it can only use N from what it touches, so if you don't till it in, it won't rob established plants below the mulch layer.

So I could use my urine soaked sawdust in my seed starter mix if I added coir and vermiculite or perlite. Maybe I will do some experiments this spring. The sawdust (cheap) would surely extend the coir and vermiculite (expensive). Marilyn

Just wondering what my permie sawdust fans think about my present, kinda urgent, devious plan:

https://permies.com/t/57597/mulch/Sheet-mulching-compensating-fresh-manure

Basically, this week, I'm going to be planting into fresh cow manure. Maybe with a tiny barrier of worm castings around each plant. I'm thinking of mixing in X proportion of fresh pine sawdust, which I can get free, to keep the fresh manure from cooking my plants. I also have SMALLish amounts of biochar, fresh and rotting straw, and fresh and rotting grass clippings I could use.

Is the sawdust a good idea? Will it take the edge off the manure? Something else better? Mix 50-50 or some other proportion?

Or (shudder) should I give up and get out the rototiller?

I have access to this field right now, for this season, and may or may not ever have access again.

Thanks!

Methinks your plants will die if planted directly into fresh anything. It really needs to be aged. That said, let me tell you what I did last year and it worked fabulously.

A little background just so you know how bad my soil was when I moved here. Last year was my first garden. Soil is totally yellow colored clay with many rocks. It is either waterlogged or cracked when it starts to dry out. Rototilling was bad and I discovered permies.com just in time. I decided never to rototill again.

So I needed a place to put the goat bedding and didn't want to make piles any more. Piles breed flies in my experience. And then it takes two years for them to break down enough to use if the pile isn't turned. Mine weren't turned.

So I was exactly like you, everything in cells waiting to be planted out. So I planted my well started tomatoes, peppers, eggplants, etc in rows three feet apart directly into the clay soil. Then I placed the fresh goat manure full of straw between the plants for mulch. Not too deep. First rain and the manure washed into the soil below and all you could see was straw on top. There was no odor and no flies! My harvest was wonderful being fed with manure tea every time it rained. I did NOT have to water the garden at all last year. Where I did not have the mulch, the soil cracked and the plants suffered. Clay you know does that. Same exact soil was constantly moist underneath where the goat mulch was even during dry spells. I couldn't wait to have to clean the barn again just so I could lay down more mulch between my waiting plants. That's a switch. LOL

By the end of summer most of the mulch had disappeared into the soil. This year it is completely gone but the clay is not cracking and I can get my broadfork into it several inches! After one season my soil is being transformed! Marilyn Kefirlady

P.S. The sawdust experiment above failed. Can't plant into sawdust. But my fresh urine soaked sawdust worked great as a mulch for my strawberry plants last fall. It smothered the weeds and the strawberry plants got huge and gave me lots of fruit this spring.

Marilyn, how did your saw dust experiment looked like? Can you give some specifics? I am experimenting with it right now as I have guinea pig urine soaked saw dust. I did experiment with wood chips mixed into the soil in the containers (larger ones also got parts of vertical rotting stumps) with some urine (I actually soaked chips in undiluted urine first, before mixing in and then after 2 weeks watered plants with more diluted ones) and plants did great. No yellowing of the leaves at all. However wood chips decompose slower than saw dust since pieces are larger. I think saw dust uses much more nitrogen per weight at the beginning.
 So I am convinced, that mixing wood chips into the soil is a great idea, if nitrogen rich material is added as well for the first 2 months or so.  
 My saw dust experiment just started a week ago, and I did 2-one with sunflower sprouts (microgreens) and one with small roses. Sunflower seeds were presoaked for regular potting mix and for experimental saw dust/urine mix (about a third of the mixture is saw dust). Regular mix sprouts showed up in 2-3 days, and saw dust ones two days later. However saw dust ones actually look healthier slightly -maybe all that nitrogen (not just nitrogen since urine is actually a very good and readily available fertilizer).
I have trouble posting photo, but you can find it in here:
https://www.flickr.com/photos/feltingme/28622503482/in/dateposted-public/
Roses were shaggy before transplanting and so far look about the same, maybe slightly yellower leaves on saw dust one, so I gave them more of liquid gold.
And here is my gardening album:
https://www.flickr.com/photos/feltingme/albums/72157626567811642
So I have to say, that so far I do not see much problems with mixing in saw dust as long as lots of nitrogen is supplied too. And in a long run it should be beneficial (moisture, aeration, etc.), but we will see. I do add mulch on top as well. Not on sunflower sprouts though as they are planted very thickly. We love them, so I almost always have a pot going.

Sawdust mixed in with potting mixes didn't work for me even though urine soaked. Killed my plants. Maybe it would work after the sawdust is completely composted. It was great for mulch in the garden.

Marilyn Kefirlady

Hmm, interesting. Did you do control plants too -same plants in similar conditions in the regular soil? My saw dust is not composted at all. Just taken straight from my guinea pig enclosure.
 How much of saw dust versus potting soil did you use? How quickly plants started showing distress? What kind of plants did you try?

I don't remember. All I know is that I am not going to waste any more time mixing half done or less than completely composted sawdust in potting mixtures. If it worked for you, great. Marilyn