I've ran 5 pick up loads of limbs through a wood chipper this week. It's piled up on top of a bunch I chipped up last year.

I've accumulated a mound about 12' long and 2' deep back there where I do my chipping.

Anybody ever had green wood mulch get hot and catch on fire? I know it's possible,...but I'm wondering how much has to pile up before you have to worry about it.

I'm thinking I may need to spread it out some.

I don't think it needs to be piled that thick for it to catch fire. Several years back I saw the fresh mulch that had been put down at K Mart smoking. I stopped by the service desk to let them know someone probably dropped a cigarette and they said almost every time they have mulch put down they have some ignite.

Yeah,...I was afraid of that. Years ago my neighbor put some kind of black wood mulch around his wood fence in his back yard and it caught fire and burned part of his fence down.

I guess I need to spread it out a bit.

Local landscaping company has a mulch pile that is at least 50 ft high & about 50ft in diameter. Gives off some steam, but hasn't caught fire that I know of in the last 20+ years.

Attracts termites around here.

I’m an arborist. Deal with mulch piles all of the time and never had a fire issue. I think the fire becomes an issue if it is in a confined space and even then, we chip into the back of chip trucks where it may sit for a couple days before being dumped.
The termite deal is a myth. Termites need structure (lumber, logs, branches, etc...) and wood chips don’t provide that. Nowhere for them to make their galleries...

I had the guys trimming high line right of ways dump truck after truck, it never caught on fire.

Back when i was logging ,and whole tree chipping i had about 2 boxes,200 cubic yards piled up for a few weeks. It would get hot and steam in the pile. Out of curiosity i took a automotive temp guage with about a 7' lead taped it to a piece of strapping and stuck it in the pile. the temperature was betwee 140-150 degrees F. at the big biomass plants where they have 1000's of yards piled up to 60 ft high they have to keep turning it over to keep it from catching fire.

Common here for sawdust piles at sawmills to catch on fire. They start on the inside and smolder for a long time.

I've got a small partially wooded lot out back. Grass won't grow under the trees so I cleared out a spot where I run the chipper. I haven't noticed it getting hot, but I've been putting a lot back there lately. I was just wondering.

Doesn't sound like you have the critical mass for fire.

Just an addition,

I took a rake and a shovel out to the mulch pile to spread it out a bit a couple of days ago.

The green stuff that I added this year seemed normal. But when I got down to the stuff that I chipped up last year it was steaming pretty good. I felt it with my hand and it was very warm. Not hot enough to ignite, but warm enough to cause me to pay attention to it.

We've got a couple of days of rain on it now. But when it dries out I'm going to spread both piles out to a thin layer.

That stuff definitely will get hot.

Are you applying this to Drywood termites or Subterranean termites?

Because Subs build their colony underground and workers travel via a constructed, atmospherically sealed mud tunnel to their source of cellulose.


I have treated several banks and commercial business for subs due to chipped, compacted mulch landscaping immediately next to the Dryvit wall panels.

Might be a good idea to go ahead and spread it out thinner now while it's wet so it'll dry out quicker.

High humidity / moisture content along with some compression are what initiate spontaneous combustion in organic materials.

A big industrial paper dust collector/automatic compactor at a place I worked at years ago was prone to start smoldering on high humidity days. Sometimes the already compacted sealed bags of waste paper dust would start smoldering and smoking days after.