Sawdust and manure compost bed

So, we recently finished milling a bunch of red pine lumber and have a mountain of very fine, damp sawdust. I ordered some mushroom spawn to experiment with some of the sawdust, and am drying some for later use but will still have plenty to spare.

Now I’m considering getting some horse or cow manure from the neighbor and making a compost pile with the sawdust. I might even do this and mulch it with straw as a garden bed to plant in next year.

My only questions are:

1. Will this turn anaerobic due to the fine texture of the sawdust and the mucky texture of fresh manure?
2. What are my target ratios of manure to sawdust? Volume would be preferred, like 1 wheelbarrow full of manure to two wheelbarrow full of sawdust?

Any advice is appreciated!

Great idea. Since the sawdust is damp, I think it will go anaerobic with too much fresh manure. IMO, that's not the end of the world if you have time to stir it and make it aerobic later. But there's no joy in dealing with an ammonia-heavy pile.

Could you stretch out the compost pile into a long row instead? More aeration surface, and easier to monitor and stir if needed.

Personally, instead of mulching over top I would chop straw into convenient lengths (6" is nice to work with) and mix it in, to absorb excess moisture and give some structure to fluff up the pile.

Ratios? Others will chime in with a more expert opinion, but with damp sawdust and damp manure, I think at least 5:1 sawdust-to-manure, and maybe as high as 10:1 if it's really wet (liquid cow poo). My 2c.

To get the right carbon nitrogen ratio you're going to want at least 10:1 manure to sawdust, more if you're using horse manure rather than cow or if there's straw or whatever mixed with the manure already.  When I mix sawdust and grass clippings I go 10 parts grass to 1 part sawdust and it's a pretty slow decomposition. I mix it up over the summer and use it the next spring. It's often not fully decomposed. I think horse manure and grass clippings are similar in the amount of nitrogen they have. Cow manure is more.

I don't know how to deal with the fact that everything is wet. If it's really wet, you could spread the sawdust outlet of a tarp to dry in the sun. I've done this before and you have to stir the sawdust around or it really holds on to moisture. It would be great for soaking up moisture from the manure if it was dry, though.

Be extremely cautious with your source of manure.  If the animal owner has been using a pre emergent to control weeds like knapweed you may not get growth.

Douglas Alpenstock wrote:Great idea. Since the sawdust is damp, I think it will go anaerobic with too much fresh manure. IMO, that's not the end of the world if you have time to stir it and make it aerobic later. But there's no joy in dealing with an ammonia-heavy pile.

Could you stretch out the compost pile into a long row instead? More aeration surface, and easier to monitor and stir if needed.

Personally, instead of mulching over top I would chop straw into convenient lengths (6" is nice to work with) and mix it in, to absorb excess moisture and give some structure to fluff up the pile.

Ratios? Others will chime in with a more expert opinion, but with damp sawdust and damp manure, I think at least 5:1 sawdust-to-manure, and maybe as high as 10:1 if it's really wet (liquid cow poo). My 2c.

I was thinking of spreading it out maybe a few inches deep over a 4’x8’ area and layering manure in with that to make a bed for next year. The straw would act as mulch, but you have a point, maybe mixing the straw in would provide aeration.

Jan White wrote:To get the right carbon nitrogen ratio you're going to want at least 10:1 manure to sawdust, more if you're using horse manure rather than cow or if there's straw or whatever mixed with the manure already.  When I mix sawdust and grass clippings I go 10 parts grass to 1 part sawdust and it's a pretty slow decomposition. I mix it up over the summer and use it the next spring. It's often not fully decomposed. I think horse manure and grass clippings are similar in the amount of nitrogen they have. Cow manure is more.

I don't know how to deal with the fact that everything is wet. If it's really wet, you could spread the sawdust outlet of a tarp to dry in the sun. I've done this before and you have to stir the sawdust around or it really holds on to moisture. It would be great for soaking up moisture from the manure if it was dry, though.

You’re saying I need way more manure than sawdust but the comment above says the opposite. Im also not sure what I’ll get for manure. The neighbor has horses but I’m not sure if he has any fresh manure this time of year, just old aged stuff. There is a cattle farm nearby though, I’m sure I could get fresh stuff there. Also, I could try to use the driest sawdust off the top layer of the pile if the wet stuff will cause issues. I have mushroom spawn to mix with the wet stuff.

Janet Reed wrote:Be extremely cautious with your source of manure.  If the animal owner has been using a pre emergent to control weeds like knapweed you may not get growth.

I was hoping to get fresh horse manure from across the street, but I’m not sure if he has any. He has a lot of aged stuff but im not sure how much time his animals spend in the stable in the summer. Seems like they’re always in the field. He definitely doesn’t spray though. They have hay fields full of various weeds. If he doesn’t have fresh stuff for me, there’s a cattle farm down the road. Im sure he has fresh stuff, but I dont know what his cows eat or what/if he sprays anything anywhere.

It’s not just the pasture…it’s the hay they eat when forage is not available.  Depending on where they get it it can completely compromise anything you grow.  And a lot of those chemicals last for years.  Just ask questions before you add any manure.  

If you look up carbon nitrogen ratio for compost, they tell you 24:1 carbon to nitrogen is the perfect ratio. Anything from 20:1 to 40:1 will work though. Maybe the range is even bigger, but that's what I aim for. I have way more carbon than nitrogen, so I go 40:1ish. Numbers for sawdust vary a lot, but it's like 300 or 400:1. Cow manure is about 30:1 and horse manure is lower, but I don't remember how much. Maybe 15 or 20:1. Since manure on its own is right in the good composting range, you don't want to add too much carbon. And sawdust is a lot of carbon.

Janet Reed wrote:It’s not just the pasture…it’s the hay they eat when forage is not available.  Depending on where they get it it can completely compromise anything you grow.  And a lot of those chemicals last for years.  Just ask questions before you add any manure.  

Good point!

Jan White wrote:If you look up carbon nitrogen ratio for compost, they tell you 24:1 carbon to nitrogen is the perfect ratio. Anything from 20:1 to 40:1 will work though. Maybe the range is even bigger, but that's what I aim for. I have way more carbon than nitrogen, so I go 40:1ish. Numbers for sawdust vary a lot, but it's like 300 or 400:1. Cow manure is about 30:1 and horse manure is lower, but I don't remember how much. Maybe 15 or 20:1. Since manure on its own is right in the good composting range, you don't want to add too much carbon. And sawdust is a lot of carbon.

So I would need a lot of manure and this would be a big pile. Plus, if its too heavy on the sawdust, it would probably be very unproductive as far as gardening goes next year.

Brody Ekberg wrote:You’re saying I need way more manure than sawdust but the comment above says the opposite.

LOL, that's what you get when you ask the Internet a question!

Looking into this further, it seems I was mistaken. I had assumed most of these manure sources were much higher in nitrogen than they are. Jan is pointing you in the right direction. It's going to take time to turn the sawdust into good soil.

You mentioned that a neighbour had well aged manure. This is prime stuff for a garden. Before applying, you can get a sample and sprout a few different broadleaf crops/weeds in it. If they grow in a funny corkscrew manner, there is substantial herbicide contamination.

Another notion: what about a "double dig" where a lot of sawdust is worked into the subsoil as a sponge for moisture and nutrients? Then build your manure-rich garden soil on top, deep enough that the roots don't interact with the subsoil layer?

Douglas Alpenstock wrote:

Looking into this further, it seems I was mistaken. I had assumed most of these manure sources were much higher in nitrogen than they are. Jan is pointing you in the right direction. It's going to take time to turn the sawdust into good soil.

You mentioned that a neighbour had well aged manure. This is prime stuff for a garden. Before applying, you can get a sample and sprout a few different broadleaf crops/weeds in it. If they grow in a funny corkscrew manner, there is substantial herbicide contamination.

Another notion: what about a "double dig" where a lot of sawdust is worked into the subsoil as a sponge for moisture and nutrients? Then build your manure-rich garden soil on top, deep enough that the roots don't interact with the subsoil layer?

I might get some of the well aged stuff to add to existing beds because some of them are in need of being topped off. But I figured most of the high levels of nitrogen have been lost in the aged manure so it might not be as helpful breaking down sawdust. I figured if I can get fresh stuff, it would balance the sawdust well and create a good compost quicker. And I thought about digging some of the sawdust in underneath the soil, but I’ve really been enjoying the lack of work and the results of no dig techniques this year. Plus, we have a decent amount of clay in our soil. Im not sure if adding more matter to hold water would be wise or not. Ive been thinking building no dig beds on top of the soil will allow for better drainage. But if working some in would help with the soil, maybe I’ll try that. Definitely need to be careful though. I found out the hard way with woodchip mulch that you really can ruin a growing season with wood if you aren’t careful with amounts, placement and planting depth.