A few days ago I wrote a bit about why intentionally putting sticks in the compost makes no sense.

I want to address this a wee bit more to explain why the sticks don’t decompose in your home compost in a time frame most people find acceptable. This is going to require a bit of science but not too much, and there’s chocolate at the end, I promise.

Before the science, I just want to clarify that some sticks and woody material will inevitably get in the compost and it isn’t as though they’re awful, just that it makes no sense to put lots of them there on purpose.

Now for the science:

Organisms in your compost are eating carbon, usually in the form of cellulose (which is around 45% carbon). That cellulose from most leaves and “tree scraps” such as paper, tissues, cardboard, etc. is relatively easy for the organisms in your compost to consume.

Sticks and chunks of tree (such as chipped trees), however, are not easy for compost organisms to access because they are sheathed in lignin. Lignin is a complex polymer and is what makes wood stiff or rigid. While leaves, newspaper and paper towels also have lignin, they have much less than woody materials.

The organisms in your compost have a difficult time breaking through that lignin sheath to get to the carbon-rich cellulose within. That’s why sticks take so long to decompose or may require multiple composting cycles before they’re finally broken down.

It’s not just you: Even at the big commercial compost facilities, sticks are screened from finished compost and go through multiple rounds before they decompose, or they just provide you with unscreened compost which includes the sticks and let you deal with them.

So when you add a bunch of sticks to your compost you are adding carbon but NOT available carbon. Organisms simply cannot access the carbon, which despite your best efforts can make your pile’s carbon:nitrogen ratio out of balance.

Adding carbon-rich material isn’t enough – the material you add needs to have AVAILABLE CARBON, because if the carbon isn’t available it might as well not be there at all. As you probably already know, that Carbon:Nitrogen balance is what gets a compost pile cooking at higher temperatures, prevents unpleasant odors, and gets you a quality finished product.

You’re a compost microbe with no arms, no hands, and the enzymes you produce can’t easily break through the wrapper – which are you going to choose?

Here’s another way to look at it (here’s the chocolate):

Pretend for a moment that you’re an organism that likes chocolate. In fact, you NEED chocolate to survive. Kind person that I am, I give you a piece of chocolate that is neatly wrapped in a wrapper.

Unfortunately, you aren’t physically capable of removing the wrapper. You’re not chemically able to remove the wrapper either. You can’t just pop the package in your mouth and even if you could, you wouldn’t get the chocolate because the wrapper won’t dissolve in your stomach.

In short, you’re totally screwed out of that chocolate you need.

The same is true of sticks placed in the compost, basically.

Organisms can’t pop the stick in their mouth and the digestive enzymes they produce cannot easily break down the lignin sheath surrounding the carbon (cellulose) they need to survive. If you’ve got a whole pile of sticks in your compost, it may be a lot of carbon but it is not AVAILABLE carbon – it is all wrapped up in a lignin wrapper that the organisms cannot break through in the time frame they need it. As a result, your C:N ratio can be off.

So adding sticks to your compost is in some respects like adding pieces of rebar or brick –  it does nothing to aid the compost and you’ll just want to remove it later anyway.

But leaves have lignin too!

While leaves have lignin as well, leaves are easier for the organisms to degrade and break down because they have significantly less lignin. Some leaves, such as oak and beech, have more lignin than most other (locally predominant) leaves but can still generally break down rapidly in a home compost pile, especially if shredded first.