How Much Will a Pile of Woodchips Decrease in Volume?

If you leave a large pile of woodchips undisturbed for an extended period, will the pile noticeably decrease in volume? If so, how much volume reduction are we talking and how soon? 10% in 6 months? 50% in a year? I assume climate and the type of wood will play a role, but I'm just trying to get a rough idea.

Background being that I'm getting ready to have a large, dangerous tree cut down on a small lot without much space. I want the arborist to just mulch anything that can't be used for carving, smoking, or firewood, but I know that it will end up being some very large piles that I won't be able to use for probably a year at least due to other projects I've got going on. With the lot being so small and very close to neighbors who are yuppies, the piles will be eye sores and I can already hear folks complaining... I reckon I could cover them with tarps.

If it makes a difference, the tree is a hickory and it's in Georgia. So humid with hot summers and mild winters.

My observation is that a large pile dose not noticeably shrink  but develops a network of mycelium in the structure of the pile and holds its shape for the first year.  Then when used become more bioavailable.  If spread out in contact with  the ground it shrinks faster as other organisms are able to consume it also.  Therefore  I recommend drawing up your permaculture plan ahead of time so that you can tell the arborist " I want this much piled here and this much spread over here.   Much less frustration for you, the arborist and your neighbors.

That is a hard one to give you an exact answer. I agree with Hans that you don't see much decrease the first year when it is in pile form. I however found that after I cracked into the 'inner' pile it was STEAMING hot from ongoing processes. This might be stoked a bit by adding some mycelium from more aggressive mushrooms like garden giants or utilizing some chip in composting processes where nitrogen is introduced.

We use a huge amount of wood chips. It will shrink some in the first year. It will rot down to almost nothing in several years. But, some of how fast it composts down depends on the equipment the company is using to chip it. Some companies have very sharp chippers and make quite fine chips. Companies with more dull blades don't chop anywhere near as fine. And then we have to pull out sticks and branches that didn't get chipped. The finer the chips, the faster the compost.

Hickory is a very fast rotter. I would imagine in a few years it would be virtually gone.

I heard somewhere that wood chips have a half life of five years.

I feel there are a lot of variables, such as amount of rainfall, humidity, snow, etc.

Mine might decrease in volume faster because I live in sunny Texas than someone in the Great White North.

Someone in wet Louisiana might see something more rapid.

With Georgia red clay that might be unpredictable.

I would reckon that in the warm and humid South those chips will be mostly gone in 2-3 years. The more spread out they are the quicker they will disappear. I have lots of places where wood chips were spread two years ago, about 5-10 cm deep, that have no recognisable chips left except for a few larger chunks. Our climate is really conducive to breaking down organic matter....

Georgia lover of woodchips here.

We moved onto a lot that had a pile of woodchips approximately 1-2 years old. The woodchips are now 3-4 years old. The pile has only shrunk a small amount in size (maybe 10%). However, it has almost fully softened/rotted with the rain, fungi, and other microbial growth. It would compress in size if we were to apply any pressure.

We later had some tree work and had a HUGE new pile of woodchips. I made an effort to spread a small amount as often as I could. This was helpful to keep it from rotting, as the "new" top layer would have a chance to dry with the exposure to air and sunlight.

I would encourage you to spread small amounts whenever you have a spare bit of time. Even 30 minutes once a week or month can make a big difference. This way, you can make use of the woodchips before they rot, and they won't become heavier with the rain. Bonus: the neighbors will know you're making an effort. If you decide to tarp, make sure there is still some airflow to slow down the warm steam and rotting process.

It's amazing how much can be spread with this "slow and steady" approach.

Thomas Tipton wrote:I heard somewhere that wood chips have a half life of five years.

Just depends a lot on where you are. I'm in the arid west and wood chips here seem about as impervious to the elements as stone.

Wow! I'm always amazed by the amount of different voices I see of this forum. It seems like whenever I try to talk about mulch with "normal" people, they just look at me blankly...

This lot is on what I would describe as a crest that slopes down on both sides. The reason I feel the need to leave them in piles right now is because I essentially have to pull out all rotting terracing and replace it before I spread any new mulch around, otherwise it'll just erode down the sides and into the water. But that project isn't one that I will get to within the next year. I want to leave the piles at the top of the crest of course because gravity currently goes down. I'll be keeping an eye on that though lol.

I'll make do with what it what I can though. When folks are saying the chips will start to rot, is that rotting in a bad way or is that meaning they will essentially turn into dirt. I know I will need some soil as well for what will basically be terrace beds, so if they chips end up not being chips in a year, will they be something that can end up going into those beds anyhow?

With wood chips, there's no such thing as "bad rotting" - they're going to turn into soil one way or another and all we get to do is influence the timespan and a few other variables. Since this is hardwood, I would definitely recommend getting some mushroom spawn going on in there. Wine caps are easy, great at breaking down the mass and adding fertility, and as a bonus are productive and tasty.

Phil Stevens wrote:With wood chips, there's no such thing as "bad rotting" - they're going to turn into soil one way or another and all we get to do is influence the timespan and a few other variables.

Yep. I'm in the arid west, up in the mountains, and our soil is pretty devoid of organic material. So trucking in small mountains of free wood chips is just an easy no brainer. Even if you use them wrong, ultimately they're still beneficial. There's just not a lot of things that you can almost infinitely add that's going to be fine but where I'm at wood chips is one of them. The only places I limit them is around the house ~10 feet out because of fire concerns, termites, and just bugs in general.

I've got a 20' flat trailer that I'm putting OSB 2x4 walls on, and grabbing what I assume to be about 7 yards of wood chips in the spring when the chippers start running to clear out fallen pine trees. They generate massive amounts of material, all free, and for $20 the landfill will spark up their loader and move as much as you like into whatever you drive in.

It also depends on the age of the wood. I chipped fresh limbs and formed a pile of about 3ft high. In a few days the pile was very hot inside and in a couple of months the pile was quite decomposed inside.

Chard Irking wrote:Wow! I'm always amazed by the amount of different voices I see of this forum. It seems like whenever I try to talk about mulch with "normal" people, they just look at me blankly...

This lot is on what I would describe as a crest that slopes down on both sides. The reason I feel the need to leave them in piles right now is because I essentially have to pull out all rotting terracing and replace it before I spread any new mulch around, otherwise it'll just erode down the sides and into the water. But that project isn't one that I will get to within the next year. I want to leave the piles at the top of the crest of course because gravity currently goes down. I'll be keeping an eye on that though lol.

I'll make do with what it what I can though. When folks are saying the chips will start to rot, is that rotting in a bad way or is that meaning they will essentially turn into dirt. I know I will need some soil as well for what will basically be terrace beds, so if they chips end up not being chips in a year, will they be something that can end up going into those beds anyhow?

Our Georgia pile of woodchips rotted from the inside-out, as expected with moisture retention and lack of sunlight. The outer layers mostly resembled dirt, but the wood-decaying fungi turned most of the interior pile white and stringy. This is wonderful for soil amendments and other purposes but may not be ideal as mulch, depending on your goals for the project. There are some great threads on Permies about using woodchips for soil amendments and other purposes. Search for "woodchips."

We have a lot of rain in our part of Georgia. For a newer pile of woodchips, it took about 8 months before the bottom layers started turning white. If you were to thin the pile and periodically expose different parts of it to sunlight, you could extend the time to utilize as mulch. Either way, it sounds as though you'll find a good use for it.