Fire-proofing Your Home Landscape With Composted Mulch

by Craig Kolodge Ph.D. (aka Dr. K)
Fire-proofing your home landscape with compost and composted mulch is an important step that can help keep your home and yard safer during fire season. Continue reading to learn why you should use it in San Diego County.
Compost and Composted Mulch plays an important role in our San Diego area landscapes providing multiple benefits
- It conserves valuable water in the soil, saving money while reducing plant stress.
- It cools soil temperatures and minimizes the heat island effect.
- It reduces weeds and herbicide use and it makes weed removal easier.
- It controls soil erosion and dust.
- It enhances the landscape’s visual aesthetics.
- Compost and composted mulch acts like a sponge to hold water to resist fire.
In spite of these positive attributes, many mulches are combustible presenting a serious hazard to home landscapes in wildfire-prone areas. A combustible material is defined as one capable of igniting, burning and supporting combustion when subjected to fire or heat. This should be taken into consideration when planting near buildings.
Working compost into the soil when planting near a home or building is a safer option than applying bark and large wood chips around plants and shrubs. Using a composted mulch with a higher percentage of fines also retains more water than mulches with larger pieces of wood for fire-resistance.
Create a Buffer Zone
It is important to create a buffer zone around your home with lower profile plants that retain water and are less likely to burn within five feet of your home. Succulents are a really good choice to use when fireproofing your landscape because they retain water and are available in a variety of colors, shapes, and sizes. Succulents have been known to survive wildfires where everything else has burned in the past. Avoid plants that have oils or resins that can catch fire easily. Using compost mixed into the soil in this area will help retain moisture for the plants and deter a fire from spreading. For tips on creating a buffer zone for your property, check out California Department of Forestry and Fire Protection’s “Defensible Space” Article. And the County of San Diego has compiled a nice suggested list of plants to use when firescaping, “Fire, Plants, Defensible Space, and You”.
Further away from the house, you can use composted mulch around your plants and trees to retain moisture, protect your plants, and deter a fire. Damp composted mulch may smolder if exposed to fire, but it is unlikely to ignite like other wood products. It is important to maintain your landscape by keeping it watered, trimming dead wood, and weeding out dry dead plants/weeds. Fire Safe Marin has a handy, easy to follow guide, “Fire Smart Landscaping Basics”, that has some helpful tips for fireproofing your landscape. Check out additional fireproofing resources at the bottom of the page.
Mulch Combustibility Field Evaluation
In 2008, the Carson City Fire Department, Nevada Tahoe Conservation District, University of Nevada and the University of California Cooperative Extension conducted a field evaluation on the combustibility of various landscape mulches. Mulch is defined as any material (organic or inorganic) used to cover soil surface for a variety of purposes.
In this study eight organic mulches were evaluated in terms of three combustion characteristics: flame height, rate of fire spread and temperature measured 4 inches and 16 inches above the mulch bed. The mulches evaluated were: Tahoe Chips (pine needles, wood chips, bark and other plant material) with and without fire retardant solution applied at 2-3 inch depth, Tahoe Chips without retardant (single 1 inch depth), Shredded Western Cedar (2-3 inch depth), Shredded Recycled Rubber (2-3 inch depth), Pine Needles (2-3 inch depth), Medium Pine Bark Nuggets (2-3 inch depth) and Composted Shredded Wood Chips (2-3 inch depth).
Each mulch treatment was replicated 3 times and allowed to settle for 79 days after installation. The plots were then ignited using a drip torch by the fire department on a hot (approx. 100 F), dry (13% RH) afternoon at the height of the fire season in northern Nevada. The Fire Rating System value for that day was “Extreme”. Fans were used to generate a mid-plot air flow of about 10-15mph.
Key Findings
All mulches were combustible under the test conditions but varied considerably in terms of the flame height and speed at which fire spread and bed temperature.
With the exception of the composted wood chips, all of the mulch treatments demonstrated active flaming combustion. The composted wood chips produced only incidental flaming with smoldering as the primary form of combustion. It should be noted that the composted wood chips out-performed the Tahoe chips treated with fire retardant.
Since only a single sourced composted wood chip was included in this field trial, it is not known if composted mulch from other sources would perform in a similar manner.
Conclusion: Composted wood chips demonstrated the least hazardous fire behavior overall of the eight mulch treatments tested and therefore would be the best choice for use in residential landscapes.
Note of Caution: All organics mulches tested are combustible and can potentially ignite wood siding, plant debris and other combustible materials in contact with or immediately adjacent to a mulch bed.
Remediation
It is crucial to remediate any damage to property as soon as possible after a fire to prevent erosion, control sediment, and remove pollutants. Fire remediation Best Management Practices (BMPs) involve protecting waterways from toxins and chemical infiltration and filtration socks (compost socks filled with mulch) excel at this.
Filtrexx® SiltSoxx® are currently being used extensively for fire remediation throughout California to prevent erosion and mitigate toxins from entering the water supply through drain inlets and other sources. They are economical, easy to install, easy to move, and very effective. Studies have shown that they do a superior job when compared to straw wattles, gravel bags, and silt fences. They are the go-to BMP tool for quickly and effectively managing large-scale fire rehabilitation in the state and nationwide. SiltSoxx® played a key role during the restoration process after the Dixie, Camp, and Valley fires.
As the only Filtrexx® manufacturer in southern California, we are proud to be providing compost filter socks for the LA fire remediation process.
We produce a variety of stormwater management products that can be used year-round to manage water and erosion on your property. Check them out so you can be prepared to battle whatever Mother Nature throws your way.
Resources and More Information
I recently provided tips and information to the Ramona Garden Club on using composted mulch to protect homes from wildfire. A key point that I shared is that compost screened to less than 1/2″ is a great option for fire suppression because it retains water (One cubic foot of compost can hold 4 gallons of water). Read about my presentation in the Ramona Sentinel article from September 15, 2021.
For a real-life example of how compost can reduce the chances of a fire on your property, read Biocycle’s article “Compost Use Conserves Water” by Nora Goldstein. You may also want to check out Cal Fire’s tips for “Fire Smart Landscaping“. Feel free to reach out to me with any questions.
The University of Nevada Cooperative Extension also has a good article on the subject, “The Combustibility of Landscape Mulches Publication”.
The U.S. Environmental Protection Agency recently published a document that outlines and praises the many uses and benefits of compost. Read the EPA’s “Environmental Value of Applying Compost: Improving Soil Health for Stormwater Management, Contaminated Site Remediation, Ecosystem Restoration, Landscaping and Agriculture” document to see why compost really is THE SOLUTION!