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Maintain a Fire-smart Landscape


General tools

When it comes to creating defensible space, the significance of proper plant and landscape maintenance cannot be overemphasized. Even the best designed landscape requires regular maintenance. Poorly maintained landscapes can easily become fire hazards – regardless of which plants are grown.

The goal of fire-smart maintenance is to reduce fuel while preserving the ecological well-being of the environment.

> Clean up
> Water/Irrigation
> Mulch
> Prune

Keep your garden neat, well-groomed, and free of excess fuel

• Remove dead plants, grass, and weeds.
• Prior to fire season, remove dead or dry leaves and pine needles from your yard, roof, and rain gutters.
• Move flammable items away from house, including plastic bins.
• Remove combustible debris on and or under decks, overhangs, and fences.
• Mow before 10 am and not on hot or windy days. Mow annual grasses and weeds to about three inches tall.
• Use string trimmers (vs. lawnmowers) for clearing vegetation.
• Stack woodpiles at least 30 feet from any structures. Clear vegetation within 10 feet of woodpiles. (One cord of firewood contains 20 million BTUs of heat energy, the equivalent of 160 gallons of gasoline. Do you want that near your home?
• Keep gasoline generators a minimum of 30 feet from any structure and 10’ from plants.
• Remove any flammable debris under propane tanks. Move propane tanks 30’from structures if fire approaches.
• Do not accumulate construction materials, recreational equipment, or other debris, including dry grass beneath patio decks or elevated porches. Screen or enclose areas below decks with wire mesh screen no larger than one-quarter inch, OR even better, attach skirting of ignition-resistant materials from the deck to the ground.
• Use equipment properly to keep from sparking a wildfire.


A precious resource – especially when fire looms

Landscapes and irrigation systems should be designed to work together. Too much water, too little water, or watering at the wrong time of year may damage plants. Watering more than necessary can encourage quick and excessive plant growth, increasing the fuel load on your property.

Water is a precious resource in our drought-prone climate. In addition to adhering to general irrigation guidelines and water conservation efforts, pay attention to these fire-smart irrigation strategies:

• Do not wet down your property on Red Flag warning days. Irrigate as normal.
• Clearly mark all emergency (and other) water sources
Create easy firefighter access to your closest emergency water source
Store an extra hose or two with emergency supplies.
• Keep hoses accessible for firefighters.
If your water comes from a well, consider purchasing an emergency generator to operate the pump during a power failure.
• Keep your drip irrigation system in good condition by checking it annually, preferably in winter or early spring. Make any necessary repairs before the dry season.

The award-winning Garden Walks program helps homeowners conserve water in their landscapes. If you would like two UC Marin Master Gardeners to visit your garden, suggest irrigation improvements, and make plant selection recommendations, please contact us.


Know what is (and isn’t) fire-smart

Mulch is a layer of material, commonly organic, spread on the soil surface. Mulch has many benefits: it improves soil quality and regulates soil temperature, reduces weeds, and helps retain water. There are many types of mulch. Common organic mulches include wood chips, leaves, grass clippings, and straw. Unfortunately, mulch can be flammable, and can pose a risk to your home if ignited. Non-combustible mulches include rock and gravel.

A 2008 University of Nevada Cooperative Extension study tested the combustibility of eight different mulches. Below is a summary of the study's findings:

Least hazardous:  Composted wood chips produced only incidental flaming with smoldering as the primary form of combustion.

When spread 2-3 inches deep, composted wood chips showed the slowest fire-spread rate.

However, these wood chips burned primarily through smoldering combustion, which might not be noticed by firefighters during a wildfire.

Nevertheless, composted wood chips were still considered the best mulch choice for residential landscapes.

Most hazardous:

Shredded rubber, pine needles and shredded western red cedar, also known as gorilla hair, demonstrated more hazardous fire behavior.

Take note:

The thickness of a wood mulch bed, wind speed, and location of the flame and building all impact the potential of mulch to ignite and how quickly fire can spread to the structures on the property.

With the exception of the composted wood chips, all of the mulches demonstrated active flaming combustion.


Mulch guidelines for defensible space zones:

Proper fire-smart use of mulch ties back to the three zones of defensible space:

ZONE 0: 0-5 feet 

Use non-combustible mulches only (stone, rock, gravel, pavers, etc.)

ZONE 1: 5-30 feet 

Use composted wood chips, but not in a widespread or continuous manner. Although it showed the slowest rate of fire spread, it is still considered a combustible material and could ignite wood siding, plant debris and other combustible materials in contact with or immediately adjacent to the mulched bed.

Separate composted wood chip areas with non-flammable materials such as gravel, rocks, decomposed granite or stone.

Limit depth of mulch to 2 inches deep.

ZONE 2: 30 feet+

Use larger, composted wood chips. Fine, stringy mulches burn faster than larger chunks.

Mulch depth of up to 3 inches is fine in this zone and beyond.
Avoid fine (less than one-quarter inch) or stringy mulches e.g., "gorilla hair"

Thick layers (more than 2 to 3 inches deep) tend to smolder and are more difficult to extinguish

Burning mulch generates embers, increasing chances of direct flame contact spreading to structures


Cut out the dead (and dried and diseased) wood

Overgrown, diseased, or dead plant material creates excess fuel that can feed the spread of fire. Reduce your risk by keeping plants and trees adequately trimmed and pruned. Depending on the plants in your garden, pruning can be an ongoing process, with different plants requiring attention at different times of the year – especially in winter. For larger trees, this may require the services of a professional arborist or pruner.

Fire-smart pruning checklist:

• Cut back woody, twiggy or overgrown shrubs that accumulate dry material (e.g. lavender).
• Cut back vines and low-growing groundcovers (e.g. ivy) to remove build-up of dry stems and dead leaves.
• Thin and reduce tree canopies to remove twiggy growth, maintain separation between trees, and reduce overall fuel load.
• Remove dead or diseased branches.
• Gently thin and trim back tree canopies to remove twiggy growth and maintain separation between trees.
• Limb up trees 6 to 15 feet from the ground or up to one-third of their height
• Avoid topping trees as this causes excessive branching, is unhealthy for the tree, and results in twiggy growth that can increase the fire hazard.