Mulch for the garden paths…and a little unexpected excitement

We noticed a tree service truck in the neighborhood that had a load of wood chips that was mainly that, wood, rather that the typical load that contains more leaves than wood. We had been thinking of a project for a long time and this finally set it into motion.

After visiting Descanso Gardens years ago, I noticed that they used their own wood chips to lay the paths through the more wild area of the garden. After fighting with the pea gravel that covered the paths when we first bought our house, I have been looking for an alternative for a long time and I thought the idea of wood chips was one of the best. We have been creating our own wood chips using our chipper-shredder, but simply didn’t have enough material to even begin to cover the paths in the garden. Pea gravel can play havoc with the blades on a chipper-shredder, so finding a solution that allowed us to clean up leaf litter without picking up the gravel was high on my list of needs.

Load of wood chip from local tree service

The wood chip as it arrived

The Mulch Pile

Spreading the mulch out and then onto the paths.

Is it hot in here?

Of course, not major project like this goes without a hitch and we had our own little bit of drama.

As you can see in the top photo, the mulch was dumped off the truck into a fairly large and fairly deep pile. While I had learned about spontaneous combustion1 in my farm town childhood – it could lead to fire in the barns in the area — I hadn’t really though about it much since moving to Los Angeles. Spontaneous combustion occurs when materials start to breakdown in an organic process. It is the very same process that creates such wonderful compost for our gardens, but if it runs away it can actually cause piles to smolder, or even ignite. Yikes!

When I went out to move some of the mulch onto the garden paths that evening, I noticed something quite worrisome. From the deepest part of the pile, steam was rising. Not only that, but there was a faint smell of smoldering wood. Hmmm, not good. I knew immediately what it was, although I hadn’t thought that it could occur in this relatively small pile of material.

Sure enough, after digging around a bit I found some areas of the pile to be extremely warm. Opening up parts of the pile would release heat and steam almost like walking into the room after someone had taken a hot shower. Time to get to work. We spent the better part of 2 hours breaking down the large pile into a wider, flatter pile — opening up any areas that appeared to be steaming. I wasn’t worried so much about the pile catching fire, but rather that a neighbor, seeing the steam rising, would call the fire department.

Luckily, spreading the pile out reduced the amount of heat any area could hold and the steaming stopped. I did notice that as we began spreading the mulch onto the paths in the back garden, there were still a few areas that were quite warm. It is my guess that the hot areas are where there were a large collection of wet green leaves. These leaves can start their breakdown very quickly and the mulch around it acts as an insulator, allowing the heat to grow more and more.

So, if you are planning on a delivery of mulch, wood chip or compost, you might want to keep an eye on it and spread it out a bit. Leaving it in a large, deep pile — even for a few hours could result in a little more excitement than you might wish.

Mulch on the paths

Mulch on the paths

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