A new factsheet (Fact Sheet 6.305) from Colorado State University Extension directs people to seek plants with low-flammability rating when planting new vegetation and landscaping.
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The factsheet directs folks to create the highest degree of protection for structures (plant only plants with scores of 8, 9 and 10 for zones 1 and 2 within the first 30’ from the home).

View the PDF Fact Sheet to review tables of low-water flowers, groundcover plants, shrubs, trees, cacti, and grasses. Plants that have lower flammability are more resistant to wildfire. Plants that have a higher flammability are less resistant to wildfire.

Attributes that decrease flammability

• Low oil or resin content
• High moisture content
• Soap, latex or pectin content
• Compact growth form
• Green stems
• Drought tolerant

Attributes that increase flammability

• High oil or resin content
• Low moisture content
• Tall growth
• Open form
• Fine wood (twiggy) stems
• High water need

The factsheet states that most of our native vegetation is adapted to fire and is flammable. Common flammable plants have flammability scores less than 8. Common flammable trees are junipers, pines, firs, and spruces. Common flammable shrubs are gambel oak, three-leaf sumac and mountain mahogany. We would discourage planting these species adjacent to the home in defensible space zones 1 and 2. If they are already present, consider replacing them with some of the recommended species listed in the factsheet.

If you decide to keep a flammable plant in your landscape, keep it pruned and thinned, remove dead material regularly, and keep it at least 30 feet from any structure or other plants. These mitigation measures are described in further detail in the Fire Resistant Landscaping Publication (6.303).