Q&A: Can mulch spontaneously combust?
The burning question...
MULCH! To paraphrase Peter Cundall "it's simply marvellous!". Bush mulch, or "Arborist mulch" is the finely chipped remains of plants and woody trees produced by tree contractors (ie. yours truly). We produce truck loads of the stuff, and it's hands down the cheapest AND best thing you can put on your garden. BUT...can it spontaneously combust causing rack and ruin?? The internet says "YES", but we're not so sure...
This totally real photo suggests that, indeed, mulch is evil and should be avoided."My mulch is hot and smoking" is what we hear most from our customers. Fear not! That 'smoke' you're seeing in the first few weeks is just steam, and the heat is produced naturally by thermophillic (heat loving and producing) bacteria. It's during this brief but frenetic time that you'll see your mulch pile reduce in size as some of the material is broken down into gardeners elixir - AKA compost. These same bacteria can't survive the high temperatures necessary for combustion, so the system is more or less self regulating, CASE CLOSED!! Or is it...?
Ah, that's some nice mulch. Where were we? Oh yes, mulch = bad, right? So under very specific circumstances a 'UGE mulch pile CAN spontaneously catch on fire, but this is unlikely to ever happen in a backyard situation. In very large commercial piles (over 3+ metres tall), vigorous biological activity can lead to an uncontrollable process known as 'chemical oxidation' (whatever that is) - basically it can get hot enough to ignite.
Look at that gorgeous tree we pruned and mulched, it's loving life and not hurting anyone!
So essentially - UNLESS you stockpile ginormous
piles of mulch AND leave the pile unturned and unwatered for a long time at over 30 degrees C and less than 30% relative humidity.......it most likely won't catch fire. Unless of course you dump hot ashes or throw a ciggy butt on your flower beds (who says common sense is dead??)
So go forth and spread your mulch freely and without care!! You're improving the health of your trees, shrubs, flowers, vegies and soil all while conserving precious water. Just remember these simple rules: a layer no more than 50 to 100mm thick and leave a gap around the trunks of trees to avoid collar rot (and don't make gigantic piles...or light it on fire...der)
