Thursday, August 30, 2012

Fire In The Hole! Potting Soil Flammability Test

Can it really start a fire in a dry plant pot?

It's summer and fire season, a time when most of us are watching for dry brush, trees and grasses that might pose a hazard around our homes and businesses.   But there is something else flammable that we might have not even considered...potting soil, dry crusty potting soil.

Dry potting soil is not easily re-hydrated and floats on water

Who would have thought such a thing possible, I mean the whole fire issue seems so far removed from growing plants in containers that why would it cross our minds?  But it is true...potting soil is flammable, actually very flammable when dry.

I got to thinking about this a couple weeks ago as I was listening to a local news story on bark mulch fires being a real problem in our area, the fellow they were interviewing showed how these types of fires often migrate up through the soil to the base of a home and can end up causing the structure to catch fire.  Now I have seen first hand a bark mulch fire caused by someone's carelessly discarded cigarette butt, and how it was migrating up toward a building just as the expert had shown.  That is what got me going on dry potting soil possibly being a danger as well since it is mostly organic matter like bark which burns readily and how we NEVER hear about it.

Then today another blogger sort of beat me to the punch when he blogged about a reported an incident of a fire that destroyed a dozen apartments where a 56 year old man lost his life and that fire began in someone's planter.   Shocking I know but it's true.  And in case you are wondering, no, dry potting soil does not self ignite, it needs a spark to set it to smoldering before it becomes a fire hazard.

With that said I got all fired up (pun intended) and decided to do a little experiment of my own just to see for myself how flammable this stuff really is and hopefully have something to show you too.  So here goes!

Safety first...water to put out the fire

I placed a handful of dry potting soil in a cast iron skillet.  Since I don't have lit cigarette butts at my disposal I used a lighter which took only a few seconds to make the potting soil smolder.

Potting soil smoldering with a little glowing spark

It is important to note that it does not matter which brand of potting soil you have, they are all equally flammable.

Five minutes into the test this is how much burned

If there would have been a good breeze blowing my little pile would have actually flamed up into a real fire. Unfortunately we had no breeze so I was stuck blowing on the smoking pile of potting soil and this is what I got.

Oh woopie

The flammability of potting soils is due to the nature of the material potting soil is made up of...and all recipes are pretty much the same with each company adding their own variations to the basic mix. These products are really not soil at all and in the industry are called "soil-less mixes".  In fact potting soil is mostly peat, bark (cedar which is very flammable when dry) and perlite.

After fifteen minutes, one third or more is burnt up

Companies also often add bits of other ingredients to make each  recipe uniquely their own but the main ingredients...bark and peat or coconut coir (husk) are always present and all are always quite flammable when dry.

So what is the take away from all this?  Two things....FIRST: Keep those containers moist so they will not be able to catch fire.  (This second one is like spitting in the wind to me because those who do it just don't seem to get how dangerous it is or if the do they just don't care.)

One of many I find at the sidewalk in front of our house
SECOND: Stop putting cigarette butts where they do not belong folks!  If wishes were fishes as my momma used to say...and I sure wish there was a way to stop people from doing this but smokers, not all but some, just don't seem to get it that those butts are dangerous.

Oh well...
Need more proof?  Here is a video showing just how fast it can happen.

Safe gardening everyone and keep those hoses handy!

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  1. Wow! I never would have thought of that!

  2. This just happened to me (thankfully with no damage). Somebody put out a cigarette in an unused (and therefore unwatered) flower pot. A few hours later, I noticed smoke coming out of said flower pot. Which I extinguished.

    Feeling like an idiot, I did a Google search on "flammable potting soil" and, shazam, this popped up. Glad to know I'm not losing my mind.

    1. Glad you found the post and were assured of your sanity!
      There were a couple of house fires here recently when someone did this. Bark mulch is another offender too. Similar products.

  3. This just happened to us as well. The only thing is nobody put a cigarette in the pot. We are trying to figure out what happened. We did find some nuts from squirrels in the soil. Also, for the past few weeks we noticed that it looked like someone took a handful of dirt and threw it on the porch this was in the same spot that the fire/smoldering was. I thought that to be very strange and just assuming that it was a bird kicking the dirt out of the pot. So unless we have a smoking squirrel, I have no clue how it started. the burning was down toward the bottom of the oblong plastic container across the front about 7 inches long. It melted the front down low and the back of the container low as well. The back in a dif area, but about 7 to 8 inches long.This plantar was attached to our house so thank god we found it smoldering when we took the dog out for a walk. Just so baffled by this. It also was not a electrical fire started in a wall. I thought that but,no. Luckily no damage to the shingles of the house.

  4. you really need to change the font of body text on this site to somehting more easily readable. My eyes hurt by the time I reached like 25% of the way down. 'Arial' or "Open Sans" should be fine.