Sawdust results in Garden

kennesawOctober 28, 2012

I tilled about 5 tons of fine dense sawdust into my 3,000 square foot garden this spring, and added 100 lbs. of urea 46% nitrogen throughout the summer. I thought I would pass along the results.

The soil has changed from clay-like to very well-drained and friable, almost like a 50/50 ground sphagnum peat moss/ soil mixture.

The soil would not support most crops this summer. The plants turned yellow from nitrogen deficiency, even with added nitrogen fertilizer, and the soil dried out quickly, even with irrigation, because the sawdust repelled water.

My fall crops, including Brussels sprouts, broccoli, carrots, lettuce, spinach and cabbage, have done very well (better than ever before) in the now partially composted sawdust/soil mixture. The soil stays moist but well drained and no additional nitrogen fertilizer was needed. It now drains so well I can even till the soil 2-3 days after a heavy rain! The soil remains loose and friable rather than clumping up.

In the 1,000 square foot area to be used for blueberries I also added 50 lbs. of sulfur. A soil test performed by Penn State produced the following results:

Ph. 4.8 (Optimum) - Was 6.5 in the spring.

Phosphate - 966 lbs. per acre (above optimum)

Potash - 991 lb./A, Slightly above optimum

Magnesium - 953 lb./A, Exceeds crop needs

Calcium - 9,095 lb./A, Exceeds crop needs

Cation Exchange Capacity - 24.2

Organic Matter - 12.8%

A soil test last spring, before adding the sawdust, found calcium and phosphate levels to be below optimum, potash to be optimum, and magnesium to be slightly above optimum. It appears that the sawdust added a large amount of phosphate and calcium to the soil, as well as adding lesser amounts of other nutrients, doubled the CEC from 12 to 24 and more than tripled the organic matter content.

Would I do this again? Absolutely - a short term setback for a long term gain! After having "clay" soil gardens at three different homes, gardening is now much more enjoyable. I no longer have to wait for a week or more of dry weather before tilling (I do far less tilling now - one pass does it). I can pull weeds roots-and-all rather then having the weeds snap off at the surface and regrow. I no longer have to wade through the mud when harvesting crops.

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rhizo_1 (North AL) zone 7

Just wondering if you have a souce for BARK fines, instead of saw dust. A double or triple ground bark is pretty good stuff.

    Bookmark   October 28, 2012 at 4:35PM
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emgardener

kennesaw,

Thanks for sharing your experience.

How much is 5 tons of sawdust by volume?
About how many inches of sawdust did you till in?
And how deeply did you till it in?
What did you use to till it in, rototiller?

Let us know how it performs after next summer's season.

    Bookmark   October 28, 2012 at 5:47PM
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rickd59

Thanks for sharing that.

A test of my soil, a clay loam, earlier this year came with a recommendation to add 6-8 yd3 of redwood sawdust/1000 ft2. I've been using trench composting instead to boost OM but I also regularly apply horse stable waste, which is mostly sawdust. I notice that it dramatically improves the tilth of my soil, reducing the large clods and stickiness. If I don't add N to the soil at the same time, I get almost no weeds in areas I've added sawdust, presumably because the microorganisms that are digesting the wood have tied up all of the N.

I've also read that decomposed wood produces the most stable type of humus in soil.

What is your plan to maintain levels of OM in your soil? Cover cropping? Compost? More sawdust or other amendments?

    Bookmark   October 28, 2012 at 11:59PM
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RpR_(3-4)

Tell us in two years when all the wood had truly decomposed what you soil is like.
I am really curious, as I have heavy black gumbo and eventually it often, after time, returns to plain old heavy black gumbo in time no matter what I put in it.

    Bookmark   October 29, 2012 at 12:54AM
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fairfield8619(Zone 8 NW LA)

Wood products are the best to improve the soil. Most bang for your buck. You are sitting pretty and glad you didn't listen to all the nannies about nitrogen. And it was SIMPLE, you didn't have to go thru all the hocus-pocus like people will tell you that you have to. It all rots in the end. It will continue to get better as time goes on. Wish I could be so lucky.

    Bookmark   October 29, 2012 at 1:45AM
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RpR_(3-4)

Did you plow it in?
How deep did you work it in?
What is you subsoil?

    Bookmark   October 29, 2012 at 12:47PM
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Lloyd

Losing a years production might be significant to some so that would be a consideration if someone else was trying to emulate this experiment.

As far as I'm aware, sawdust doesn't contain much in the way of nutrients. Making the soil easier to work with certainly has benefits but I'd bet a good quality compost would do that and more.

Lloyd

    Bookmark   October 29, 2012 at 1:27PM
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luckygal(3b)

Thanks for sharing your 'experiment' with sawdust.

I think it's important to say that all sawdusts are not equal. Results likely depend on type of wood and age of the sawdust.

I've used free sawdust for years as the brown in my compost used exclusively as mulch. Source is a small mill that uses mostly pine, but also spruce and fir.

I'm trying a different experiment this year as found a source of free bark shavings from a log home builder (only had to pay trucking). This material was already beginning to decompose - parts of it looked like soil and it heated when left in a pile. I've not tilled it in but have heavily mulched my perennial garden with it. Will watch to see if there is nitrogen deficiency but expect there will not be. I use alfalfa tea as fertilizer anyhow so that should prevent any problems.

Sawdust makes a wonderful mulch and many commercial berry producers use it. Good to hear it can also be tilled in to improve clay soil. In many areas sawdust is easier to find than a quality compost so using it to lighten clay soil and adding nitrogen, smaller amounts of compost, and fertilizer if necessary seems to be a good option.

    Bookmark   October 29, 2012 at 2:19PM
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kennesaw

Answers to your questions:

How much is 5 tons of sawdust by volume? - Answer: 10 full-size pickup truck loads of bagged sawdust.

About how many inches of sawdust did you till in? Answer: About 4 inches.

And how deeply did you till it in? - Answer: About 7-8 inches.

What did you use to till it in, rototiller? � Answer: 9-hp rear tine rototiller.

What is your plan to maintain levels of OM in your soil? Cover cropping? Compost? More sawdust or other amendments? - Answer: Whatever OM is available, grass clippings, leaves, sawdust etc., to be used for mulching only, to be tilled in at the end of the growing season.

What is you subsoil? � Answer: Red clay. The garden is on a sight to moderate slope, so drainage is not an issue. The grass surrounding the garden filters out any soil from the runoff during heavy rains. .

Making the soil easier to work with certainly has benefits but I'd bet a good quality compost would do that and more. - Answer: Yes good compost would be "best", but that was not an option. I did not want 5 ton sawdust compost pile in my yard, nor was I willing to pay several hundred dollars to purchase compost.

    Bookmark   October 29, 2012 at 2:27PM
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RpR_(3-4)

What was the cost for the nitrogen?

    Bookmark   October 29, 2012 at 2:55PM
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jonfrum(6)

The only real difference between incorporating sawdust and peat in your soil is that the sawdust has a greater surface area, so it will break down faster, and draw nitrogen out of the soil proportionally. Balancing added nitrogen to account for the decomposers is going to be tricky if you're growing crops at the same time. A year later, you're golden.

    Bookmark   October 29, 2012 at 3:50PM
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fairfield8619(Zone 8 NW LA)

I love it when somebody says use a "good quality compost" as if everyone has access to it and can afford it. I don't think kennesaw was expecting much. When you have heavy clay the last thing to worry about is Nutrients. You need to improve the texture or nutrients are a moot point. If the plants die because they sit in soggy soil then there's no need for nutrients! Around here the closest you get to "compost" is "landscape mix"- ground up yard waste that has sit for a while. The vast majority of initial N depletion happens in the first few months and goes downhill from there. Mulching with any organic matter without digging it in will not deplete the N.

    Bookmark   October 29, 2012 at 5:40PM
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Lloyd

I don't think anyone here said "use a good quality compost".

Lloyd

    Bookmark   October 29, 2012 at 7:35PM
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dottyinduncan(z8b coastal BC)

Thanks for sharing your findings. A few years ago, I got a few bags of sawdust mixed with chicken manure. One of them went into a tiny little flower bed, quite a large amount for such a small bed. Every year since, I have been delighted to plunge a spade into the bed each spring! The spade almost disappears because the soil is so light and friable and very easy to dig. given the clay soil everywhere else on the property and the hardness of it, this little bed gives me pleasure. I expect that the combo of sawdust and chicken poo is similar to your sawdust and nitrogen.

    Bookmark   October 29, 2012 at 7:40PM
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wayne_5 zone 6a Central Indiana

This is interesting. Kennesaw said that 4 inches of sawdust was mixed into the soil for 7 to 8 inches. I too have found that 4 inches of local sphagnum peat moss does a similar loosening job on clayish soils....so very nice to work with. The peat has no delay effect as it is fairly inert, and acts mainly as a soil conditioner.

    Bookmark   October 29, 2012 at 8:38PM
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fairfield8619(Zone 8 NW LA)

pt03, I think you have a memory problem.

    Bookmark   October 29, 2012 at 10:44PM
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strobiculate

#sets up popcorn concession# and sets up lawn chairs.

there's no reason you both can't be wrong. no one said use...but some one suggested similar or better results from.

my favorite part around. anyone for lemonade?

    Bookmark   October 30, 2012 at 1:07AM
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kennesaw

What was the cost for the nitrogen? Answer: $20 dollars per 50 lb. bag of urea (46% nitrogen). I used 2 baqs over the spring and summer.

    Bookmark   October 30, 2012 at 7:57AM
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Lloyd

For sure my memory is not what it used to be, but in this instance I don't think it is failing me quite yet. I do think some people are having a comprehension problem though. Having said that, I'm willing to stand corrected if a quote could be found.

Lloyd

    Bookmark   October 30, 2012 at 8:39AM
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fairfield8619(Zone 8 NW LA)

Oh my, Lloyd, here you said:

As far as I'm aware, sawdust doesn't contain much in the way of nutrients. Making the soil easier to work with certainly has benefits but I'd bet a good quality compost would do that and more.

Lloyd
Remember that? The inference is clear, I don't see how it could be otherwise. Cut and pasted directly from your post on Mon, Oct 29, 12 at 19:35

    Bookmark   October 30, 2012 at 10:15AM
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Lloyd

I'll take my response off line.

    Bookmark   October 30, 2012 at 10:42AM
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toxcrusadr(Zone 6a - MO)

Good Lord, the whole Northeast just got bombed back to the stone age, and we're arguing about compost? :-D

    Bookmark   October 30, 2012 at 11:02AM
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Lloyd

He started it! ;-)

Lloyd

    Bookmark   October 30, 2012 at 12:29PM
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luckygal(3b)

LOL guys, let's leave the picky, picky to women where it belongs! ;D LOLOL Even ignorant little me has used the term "good quality compost" a few times. I doubt there is anyone who has been on this forum any length of time who is not aware there are various qualities of compost. Even clay soil does not deserve a compost made with materials saturated with chemicals that will harm their plants. That might be termed 'bad quality compost'.

We all need to keep in mind that we don't all have access to abundant amounts of compost, sawdust, or any one particular amendment. I consider myself fortunate that I live in an area where lumbering is big business and compost is free for the shoveling. Compost I'd have to buy and it's not inexpensive.

This thread has been an eye opener to me and I'm wondering if I should begin another project using sawdust to amend a larger area. Thanks kennesaw (I think!). I'm curious to know if you had to pay for the sawdust you used and if so what was the cost?

AND please, please, please, let us not turn this thread into another peat bashing thread. There are enough of those around.

    Bookmark   October 30, 2012 at 4:05PM
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toxcrusadr(Zone 6a - MO)

Who is this Pete Moss and why is he getting bashed?

    Bookmark   October 30, 2012 at 4:10PM
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wayne_5 zone 6a Central Indiana

Who is Pete? I think he is that rascal that owns/leases about 270 million acres in Canada. Little Pete lives near me...about 10 acres.

I think Pete gets bashed because it's the pc thing to do.

    Bookmark   October 30, 2012 at 4:25PM
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Lloyd

I feel kind of lousy for responding to tox with humour, there is nothing funny about this storm and it was inappropriate to do so. Sorry gang.

Lloyd

    Bookmark   October 30, 2012 at 6:04PM
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kennesaw

In response to the question about how much I paid for the sawdust, I paid $1.00 for each 50-60 lb. bag. The bagged sawdust was also easier to transport the 200 feet from my pickup truck to the garden than bulk materials. It was very easy to blow away any sawdust residue off my pickup truck and driveway using a leaf blower. Most mulches and composts contain 50% or more moisture. Dry sawdust probably contains about 10% moisture. For me it was a very cost-effective, time-efficient method of improving my garden soil. Of course, sawdust amending would not work as well in a dry or cold climate, where the decomposition would be much slower.

    Bookmark   October 30, 2012 at 9:43PM
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2ajsmama

I'm interested in the comment that many commercial berry growers use sawdust as mulch. Can you elaborate? Hardwood, softwood, how finely ground (really a dust? or more like chips/ground?).

I have access to very fine hardwood (mostly maple, some cherry) sawdust from furniture shop, I tried it as soil amendment in past and even mixed with N source (tested OK) my plants did not do well in that bed. Too fine to use as mulch (blows away when dry, repels water when wet) or in compost (tends to sift down through pile and settle). I do have a few raised beds (app 1ft x 25ft each) of brambles, had mulched with decomposed wood chips in spring but those are fully decomposed now, covered roots with burlap during recent freeze but I'm looking for a good winter mulch to put over/under burlap now. Was thinking shredded maple/oak leaves.

    Bookmark   November 1, 2012 at 8:52AM
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Dalmatian

Gee Guys, I write from downunder - Blue Mountains, west of Sydney. I am ex-UK. They call me a pommie winger. In England they would call you "old Farts" or even "old Tarts". Me, I reckon you are a pack of Shielas. That said, I enjoyed your contributions - nothing like a beer and a good barney.
O.K. exactly what do you call hardwood. I know you have eucalyptus in California. With old eucalyptus floor boards - you have to drill before you can knock a nail in. River red gum is used as a bearing plate under footings and will last for ever; say 2 or 3 generations at least in poor swampy ground. Untreated iron bark utlity poles are good for 30+ years - even the white ants have a hard time to get a meal. Aussie Oak some might class as hardwood; English Oak is debatable - but neither are true hardwood.
Mulching with hardwood chips - 2 to 3 years, dig em in and no problem. I left a truck load of harwood chips about 5 or 6 years - grass grew over them after they had settled. I eventually dug them in. So instead of gravel, I have woody, leafy bits to give the soil an open workable texture. I am only a weekend, fair enough is good enough. Here we use a potting mix which is "quality" soil with very small wood and bark chips.
Keep smiling, Regards to You All; Bill the stirer.

    Bookmark   November 1, 2012 at 11:14AM
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emgardener

kennesaw,
Thanks again.

This is the info I'm adding to my gardening files:

46 lbs of nitrogen over 3,000 sq ft was not enough to overcome nitrogen lockup of 4" of sawdust dug in 8".
But second season crop didn't need fertilizer.

Someday I may move and have a big garden like yours and this info would be useful.

cheers

    Bookmark   November 1, 2012 at 4:04PM
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jaf1953

I have just bought a house that had had a pine tree removed leaving a deep 3-6" depth of sawdust over a 20 X 20 area. Is there anything I can do to help this sawdust decompose? Should I be trying to till it into my soil?

I hate the idea of just trying scrape it all up and cart it away.

Thanks.

    Bookmark   January 18, 2014 at 8:37PM
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paleogardener(9)

Use it as mulch, mix it into your compost batch, till it in, just don't cart it away!:)

    Bookmark   January 18, 2014 at 9:25PM
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pnbrown

Jane, is it the chips from the chainsaws that you have? That is quite a bit more coarse than what is typically meant by saw "dust", which is the debris from a circular saw of some kind.

    Bookmark   January 20, 2014 at 6:49AM
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jaf1953

I don't know for sure since this is inherited when I bought the house, but it looks similar to what I've seen before from stump grinding - so pretty fine and finer than a standard chipper would produce.

    Bookmark   January 20, 2014 at 8:44PM
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toxcrusadr(Zone 6a - MO)

How long has it been on the ground? Weeks, months or years?

    Bookmark   January 21, 2014 at 11:40AM
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