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.

Published by

Linda Chalker-Scott

Dr. Linda Chalker-Scott has a Ph.D. in Horticulture from Oregon State University and is an ISA certified arborist and an ASCA consulting arborist. She is WSU’s Extension Urban Horticulturist and a Professor in the Department of Horticulture, and holds two affiliate associate professor positions at University of Washington. She conducts research in applied plant and soil sciences, publishing the results in scientific articles and university Extension fact sheets. Linda also is the award-winning author of five books: the horticultural myth-busting The Informed Gardener (2008) and The Informed Gardener Blooms Again (2010) from the University of Washington Press and Sustainable Landscapes and Gardens: Good Science – Practical Application (2009) from GFG Publishing, Inc., and How Plants Work: The Science Behind the Amazing Things Plants Do from Timber Press (2015). Her latest effort is an update of Art Kruckeberg’s Gardening with Native Plants of the Pacific Northwest from UW Press (2019). In 2018 Linda was featured in a video series – The Science of Gardening – produced by The Great Courses. She also is one of the Garden Professors – a group of academic colleagues who educate and entertain through their blog and Facebook pages. Linda’s contribution to gardeners was recognized in 2017 by the Association for Garden Communicators as the first recipient of their Cynthia Westcott Scientific Writing Award. "The Garden Professors" Facebook page - "The Garden Professors" Facebook group - Books:

7 thoughts on “Making your landscape fire resistant during wildfire season”

  1. We are just back from Vancouver Island. Timing is such that we did not experience the wildfire smoke working its way north and west. While moisture-rich soils are one proactive tactic to lessen property losses, so are steel roofs. I am amazed at how many shingled roofs we saw in the wooded areas where we vacationed.

  2. It really makes me angry when I see homes gone up in smoke or going up in smoke on TV.It is not rocket science to fire proof a home and yard. It only takes basic intelligence and good common sense.

    I remember many yrs ago,(around 10 or more) when the fires ravaged the Santa Ana mountains, which had 1000s of expensive homes on the mountain ridge and all over. After the fire had gone through and smoke disappeared there was one home untouched. The owner used his head well ahead of time, and installed a good sprinkler system around his property and on the roof of his home. When the fire came near he turned it on.

    People who do not think, deserve what they get!

  3. There are even incredible business opportunities for lawn sprinkler companies, and indoor fire sprinkler systems who know all about water and pressure and sprinkler systems to go door to door or advertise on line to do these kinds of custom installations.

    It is not rocket science and simple basic installations could easily done for a couple thousand dollars. By even one competent man in one day. He can make himself a grand a day. If an installation needs a back up generator, extra pump, and back up water supply, that is not all that expensive either. Sure is cheaper than a house. Most home owners should be capable of doing this themselves.

    It escapes my mind, or imagination, why there aren’t people out there doing that.

    If I was an insurance company, I would not insure a home without this system, in prone areas.

    Similar point to goes to proofing homes against tornadoes and hurricanes. I have seen shows on home improvement channel, doing this. Costs more money than a sprinkler systems, but sure is cheaper than replacing a house and other buildings. And lower the cost of insurance.

  4. Not specifically fire related question but this is your most recent post on mulch that I find. I hand chop all cuttings and let the leaves lie too, but my biggest source is bagged pine bark mulch. I recently spread this mulch around river birch and dogwood. Is this a mistake? So this is not the best, but now it may even be harmful because it sheds water? . I’m confused by conflicting information and want to do the best to preserve what I have. Thank you.

    1. Bark mulch has a lot of waxy substances which neither absorb water nor encourage colonization of roots and fungi. Both of these things mean it’s a dry mulch and more likely to burn than wood mulch. So yes, it’s bad for reducing the likelihood of fire and doesn’t do much for soil life.

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