sawdust/ grass clipping debacle- advice needed

Okay- first- we thought we were pretty good at compost until we didn't (yet) succeed in composting this year. We have an inexhaustible supply of alder wood sawdust and grass clippings. We figured- mix them together and what can go wrong? Well- our two fairly large (4' x4' x 5') piles did not compost. The ratio was about half and half sawdust and grass clippings, maybe too much of one or the other? The centers seemed completely dry after 9months, so we figured the tops matted and prevented rain from entering. We're also thinking the mix was too "fluffy". Any other advice? Manure in any quantity is not super easy for us to get, but can be procured. We mixed the piles and stirred them, stomped them and added kitchen compost but the pile still seems cold to us. We just got another load of both sawdust and clippings and I'm fishing for advice before we proceed. Thanks!

Sounds to me like the whole thing is really high in carbon. I was trying to compost sawdust earlier this year in a homemade tumbler and I couldn't get it to heat up until I made half the volume fresh clover and a few shovel fulls of debris from the chicken yard which I think was mostly useful as inoculant. It got really hot really fast.

Pee on it!

The questions that first come to mind....
...did you initially moisten the pile as you were making it by adding water, for example- spraying each layer with a hose?
...did the pile heat up at all during the first 3 weeks? Did it get hot enough that the material would have been uncomfortable to hand dig into or hold barehanded?
...did you re-moisten as needed as the pile got hot and drove moisture out?
...did you cover the pile in some manner to hold moisture in...or if in a rainy area, to keep excess water out?
...did you just layer the material or did you mix it up?
...were the grass clippings fresh cut or were they a couple days old or older?

I dug into a huge pile of wood chips a few weeks ago and noticed a similar thing - the outside was lovely dark moist humus, the core was dry and uncomposted. We hadn't deliberately added water, it was just left as the van had dumped it. Personally it didn't bother me as I wanted it for a surface mulch, but if I was composting I would have to both add water at the start and I figured that making it volcano shaped would help any rain water that falls on it to infiltrate rather than run off.

Lots of great advice for you here Diane. Su Ba has hit on some very important points and I just want to emphasize one ... how "fresh" are the grass clippings? Fresh grass clippings are a source of nitrogen but it's not long-lived (like manure). Grass clippings quickly form a mat and repel moisture and inhibit air flow ... that's why they make such a great "kill mulch".

It sounds like you really have a lack of nitrogen (or an excess of carbon) and also not enough moisture. As Alder said, "Pee on it." ... seriously. Collect all available urine and soak the pile.

Good luck and keep working at it. Maybe you can find some manure somewhere.

-Tom

Su Ba is right...Assuming you have fairly fresh grass clippings, you need to moisten each layer as you build the pile (especially the dry sawdust/wood chips).
It's been written over and over that the heap should be as wet as a wrung out sponge, but I always make mine a bit wetter than that.
Taking a lesson from activated compost tea, I use a hose end sprayer to lace the water with diluted molasses as the sugar supercharges the bacteria. Although not absolutely necessary, you might also be best served by adding some finished compost or some good soil to act as an activator to kick start the biology.

The pile should heat up to 100-120 (the goal is 130-140F as the pile is turned) by the next day (if you don't have one, you should invest in a compost thermometer).
It's also been written that you should turn the pile when the temperature drops. This is incorrect as it means the thermophile bacteria are dying off. Initially, I wait 4 days, then I will mix, turn and re-stack the heap every 2 days (not unlike the Berkly method). Now I use my little Mantis tiller with straight tines to break the pile down. It chops and mixes the pile well then I re-stack, again adding the diluted molasses water as needed to ensure ample moisture.

This method should yield finished compost in 2 weeks or less!

The Mantis, I find, works great for opening up and mixing compost piles. Sure saves my back! And it processes a big pile a lot faster than I could with a fork or shovel.

Lots of good suggestions so far. I would probably rake up a bunch of brown leaves from the forest, add to pile, various wild mushrooms if you find them. Add double or more of the grass clippings, add milk or bread if you can find it, grind the sawdust and everything else you can imagine together with a lawnmower...re-pile the heap at least 3' tall. Keep the top of the heap somewhat opened for rain, don't use city water if you can help it. Sawdust is inherently difficult to process, not impossible, but generally slower than brown leaves & grass clippings. Don't add alkaline substances (lime) if you can help it, keep it generally on the acidic side, it will somewhat neutralize upon completion of the organic processing.

If you must use it soon, it is probably only good as a mulch, it is too light and not fully processed to actually grow stuff thru the whole season. At end of season rake it all back together again & try it again. Sawdust is hard to break down.

james beam

Wow! Thank you all so much for all the great advice. Pee- well- I'll see what we can do! That would be a lot of pee! With last years uncomposted mix and this new mix we have a HUGE pile that we are making into a 4' row along the back of our garden. We're mixing in some donated manure, a garbage can of kitchen waste, and this time I will keep it much more moist. The clippings don't get into the pile until they are a few days (or more) old and they were bagged so we were more careful about breaking up mats this time around, and we've kept the sawdust to a minimum. We have added leaves and more soil. Mushrooms are a good idea too. I'm generally a lazy composter and prefer to wait years rather than turn, but this time we are committed to turning this monster! The sawdust is very finely ground already. I will keep you posted. It looks like this 4' pile might very long!

also- we do not need this compost soon, but I'd like it for next year or the year after.

I'm sure you will have success eventually! But the spring & summer are really good times to compost because of the natural summer heat, & green grass availability. It was impossible for me to add anything green to my compost pile during last winter...for example. I would be a little careful adding more sawdust to the old batch trying to complete 'one huge batch', of course you should add to your old batch whatever you think right to force it to activate again.

Composting sawdust requires more water than composting just leaves. Once the sawdust 'core begins working' I wouldn't add water unless you think it necessary.

If you have room you may want to start a new batch nearby for your new bulk sawdust & related, otherwise adding the new sawdust to the existing batch will cause the thing to take longer to fully process. In this way, you will get a better idea of what it takes to fully process a large batch. A little shade goes a long way if your turning a huge pile in July! If you find any extra earth worms while gardening...throw them at your compost pile.

james beam

I completely agree with not adding more sawdust/ grass clippings to the old pile, but we've "merged" them into a pile where the old and new are back to back, if that makes any sense. Our logic for making a "line" of compost is that we can turn it more easily. We made it Saturday, soaked it, and this morning I got a nice warm feeling off all parts of it so definitely we have something this time. In addition to mixing more we also stomped down the mix so it wasn't so fluffy, added kelp meal and some manure, and again, watered it as we went.

Hi Diane
If you visit this link and select the compost guide it should help you out. This site is geared for composting horse manure but the principles are the same.
One of the best ways to tell your compost is active and working is to invest in a compost thermometer that is approx 20" long.

Manure maven

Here's an image of a batch of wood shavings based compost I made up a short time ago.

Along with not enough moisture I think your carbon ratio is probably too high. You have to figure saw dust has a surface area that is extremely large because it is so fine. So it's likely that you are adding more carbon than you think. In terms of moisture it has been my experience that a tarp or cardboard placed over the top of the pile helps maintain evaporated moisture....don't cover too right though because you'll cut off air flow. If you reach into the pile at any point and pull out a handful and squeeze it you should get at least a few drops of moisture dripping from your hand...if not you probably needed to must the pile for 5-10 minutes or, if it's really dry, turn the pile and add water during that whole process.

I like the urine and molasses-water ideas.

Just learned that the thermophilic bacteria (the ones that initially heat things up hot enough to kill weed seed) love sugars.
The next round likes the complex carbs and protein and then after it's cooled down you get the fungi working on the cellulose, lignin, etc (the tough woody bits).

Fresh grass (that is still giving off that wheatgrass smell) should have sugars still present.
Flowers do too - if you are trimming dandelions out of the lawn, or pruning, or have any flowering weeds, those might help if they go in fresh.
You could also add apple-peels, cooked potato-peels, etc, if you can get them.

Let's see.... what makes tough bits into sugars faster? Mushrooms do sound good. If there's not enough of the N and sugars to heat it up, maybe you can even skip ahead and get the mycelia going now. Then once the sawdust has broken down a bit you might see the pile revert to what you'd expect from compost, bacterial heating-up.
Spit has an enzyme that makes starches into sugars, called amylase. Got any herbivorous animals that drool a lot? Maybe you could spit in the bucket of molasses-water a few times, let it ferment a bit, then dose the pile.
(I am totally making this spitting-in-the-molasses part up from unrelated knowledge-bits, but I think it could work. Couldn't hurt, anyway.)

Presumably if you had a lot more kitchen scraps, you'd be using them. I've heard of using molasses and cornmeal, or any grain powder, under black plastic as a super-hot composting weed-suppression method. Worked pretty well when our landlady tried it in Portland, and you can get horse-feed grade molasses that's very reasonable by the 5-gal bucket. Any grain - maybe flour that got meal-moths in it, or whatever - will boost those sugars, and if applied by rinsing it through the layers with water, it should kick-start pretty soon.

I think the moisture will help more than anything.
Our dry climate means we routinely have to wait several years; Mariah Cornwoman puts sprinklers and tarps on her piles, layered for aeration, and gives them about 3-4 years. The dry parts stall out, have to be rearranged and sprinkled again. (artesian well, not city water)


Note on experience level: I am not a big-time composter by any means.
Since I rarely keep up with the whole garden area anyway, I've started just piling things up directly over one of the sunken log/dirt/mulch beds, in hopes of having a kick-ass mulch bed by the time I work my way over to that side of the plot some years hence. I sheet-mulch with the weeds and old hay, and sawdust / wood chip as well as old hay goes around the blueberries. Acid-loving little pets, they are.
My latest big pile of kitchen scraps (we had a freezer go unplugged last month) just went into the new hugel bed.

I know the theory of composting to kill weed seeds etc, but with our very cold winters I have about half the year to work with; and with the dry, dry summer and fall it's realistically about 2 months (late April - early June) that compost would naturally happen around here. The rest of the time it would need sprinklers, then a big insulated pit like a reverse ice-house or something. And I'd need to move it at least twice, not to mention turning it.

I find that seed-grown weeds are not that hard to pull, and any bare dirt gets seeded by all the other weeds in the pasture anyway. So I don't see much point in putting the time into a weed-seed-free compost, when I can mulch with the same materials and see the dirt improve in a quarter of the time. The mulched beds have delicious soil, and the current crop of weeds just became more mulch, with today's seeds planted where the weeds got pulled.

This is a small-time hobby garden; I could totally see it being more interesting at the industrial scale, if you're farming with more equipment and less labor per acre.

-Erica

Great advice everyone! We made another pile with a higher grass clipping ration this time, added huge amounts of vegi waste and much less sawdust (but some) and now have a GREAT pile- one week into it its 1/2 the size and very hot. I've made deep paths throughout my garden with the sawdust now. When I had a community garden plot in Seattle we used sawdust in the paths. There, the sawdust can decompose slowly and suppress weeds. Every other year, once the sawdust was nice and aged and full of worms, we'd add it to the beds and start over with new sawdust. Its still a nice carbon for the compost but much less than we put in last years compost is good. I don't have a photo of my compost but it pretty much looks like this: https://www.youtube.com/watch?v=04Zz-GRPAzA

If you don't need the compost until next year or beyond, don't bother trying to make it hot....and fine for cold heaps, but never put worms into a heap that may heat up lest they become part of the process. There are some experts that feel that cold compost is better than hot....so you could just pile it all in a heap, keep it moist and just let nature take it's course. Using the saw dust in walkways is a great idea...I'm planning to use chips.
Alternatively to composting, you might use much of the material directly on garden beds as mulch...again letting nature take it's course and saving the labor of moving. stacking, turning, moving the materials!

Consider using your sawdust with mushrooms for mushroom compost.
You may be able to get some eating mushrooms out of this as well as compost.

Compost can be bacteria based like in grasslands. However, compost can be fungus based like in woodlands also.

Update- you were all right that said there was too much carbon. This pile did take many years to compost. The plus is that the soil there is now fantastic 9 years later. We use the sawdust in the paths now only and recycle the paths into the garden soil every few years. We dont' have anymore grass so that's nice.