Invasive grasses might have played a part in the deadly wildfires that burned Lahaina, Hawaii recently. The grasses have taken over land that was once occupied by crops like sugar and pineapple.
Michele Steinberg is wildfire division director at the National Fire Protection Association. She said some plants are more flammable than others. But, she noted, “there is no such thing as a fireproof plant.” All plants can catch fire under the right conditions.
Those conditions include poor pruning, lack of watering, and letting dry, dead plant parts remain on the soil surface in high-risk areas.
If you are selecting plants for your garden, knowing which plants offer some fire resistance and which are more flammable can serve you well.
Quicker to catch fire
Plants that produce flammable substances, like aromatic oils, resins, waxes, or sap, are among the quickest to catch fire. They will often catch fire even if they have been well-watered and cared for. They include bamboo, rosemary, and eucalyptus.
Trees with papery bark that falls off, like river birch, are usually more flammable than those without. And fine-needled plants like pine, juniper, and spruce contain saps and resins. Their needle-like leaves increase the risk of fire when left on the ground or on the top of a house.
Many grasses are highly flammable. Their ability to ignite increases when they are left to stand dry over winter or during periods without rain. Additionally, too much heat dries out the soil and under such conditions, many kinds of plants turn into a fire starter.
Native vs. non-native
As a group, “native plants aren’t necessarily less flammable” than introduced kinds of plants, Steinberg said.
But nonnative, invasive plants often are a greater fire risk because they spread quickly and are usually left alone by wildlife. The nonnative plants spread faster than native plants, and often tolerate heat, lack of rain and heavy rain better.
For the best fire resistance, choose deciduous trees, like ash, crabapple, and maple, over fine-needled trees. Plants like succulents with water-filled leaves are slow to burn. They include ice plants and sedums. Some groundcover plants, like ajuga and creeping phlox, are also slow burners.
What to look for in plants
The Washington State University Extension Service has published advice for choosing plants that are fire-resistant. Qualities that make a plant less likely to burn include:
• High water content in leaves (these ignite and burn more slowly).
• Little or no seasonal gain of dead plant material.
• Open branching (they provide less fuel for fires).
• Fewer total branches and leaves (again, less fuel for fires).
• Slow-growing, so less pruning is required (to keep open structure as noted above).
• Non-flammable material on the plant, like resins, oil, or wax.
I’m Gregory Stachel.