Making your landscape fire resistant during wildfire season

Wildfires are increasingly threatening urban areas. Photo from Wikimedia.

This topic may have no relevance to where you live – but it’s very much front and center here in western Washington this summer. Our naturally droughty summers have gotten longer, hotter, and drier thanks to climate change. Wildfires are ravaging all of the west coast, on both sides of the Cascade mountains. And one of the recommendations I see for fire-proofing your landscape is to remove all wood-based mulch. While this might seem logical, it’s not. And here’s why.

Not all wood mulches are equal. Wood chip mulches, which readily absorb water, are different than bark mulches, which can be quite impervious to water based on the type of bark and how fresh it is. The waxy components of bark not only make it resistant to water movement, they also more likely to burn. Likewise, pine needles, cones, straw, and other coarse organic mulches absorb little water and easily ignite. They should be avoided in fire-prone areas.

Pine needles and pinecones are a natural mulch layer in pine forests – but they burn readily. Photo by Pxfuel.

Wood chips are one of the least flammable mulches, and if landscape plants are properly irrigated, the wood chip layer is going to be increasingly moist as you work your way down to the soil. This reduces flammability, while maintaining plant health. And healthy plants are more likely to survive fires than water-stressed plants – because they are full of water. (Oh, and those “flammability lists” of plants you might see? Dr. Jim Downer has already debunked that approach.)

Rubber mulches are the very worst choice you can make for a wildfire-resistant landscape. They burn readily and they burn hot.

The best way to reduce wildfire damage to your planted landscape is to keep it irrigated. Bare soil is a no-no in planted landscapes, regardless of what you might see recommended elsewhere. A well-hydrated landscape with green lawns and healthy trees and shrubs is not going to catch fire from a spark or ember. And it might even survive a fast-moving wildfire.

Yes, it takes water to protect a planted landscape from fire. If consistent irrigation isn’t feasible, you might want to rethink your plantings.

We saw this in eastern Washington this week, where the small town of Malden was 80% destroyed by a fast-moving fire. But some homes were spared – why? Whitman County Sheriff Brett Meyers pointed out “those people that had some green and some buffer around their home were able to maintain their homes.”  

Did these houses survive because of a green buffer?

So while it may seem counterintuitive to keep woody debris on your soil, look at the whole system – not just a piece of it. If you don’t have plants anywhere near your house, then bare soil is the way to go. But for planted landscapes, wood chip mulch is part of the solution – not the problem.