Vegetation between houses can either add fuel to the flames during a wildfire or help to slow fire spread.
When highly flammable plants like Leyland cypress, arborvitae, junipers or Italian cypress are used for privacy screening, they can ignite easily, burn intensely and quickly spread fire to your home or between structures (scroll down to see the impact of privacy shrubs in an Ashland wildfire).
Because fire-resistant plants are more difficult to ignite and burn, they are recommended for privacy screenings between homes.
The 2012 OSU Extension Publication Fire Resistant Shrubs and Trees for Privacy in Southwestern Oregoncontains suggestions for shrubs and trees recommended for privacy plantings that meet a variety of growing conditions and requirements. This publication provides examples of fire-resistant shrubs and trees that can be used to create a more fire-safe home landscape while providing the privacy you desire.
Generally, highly flammable plants have:
Fine, dry, or dead material within the plant, such as twigs, needles and leaves
Volatile waxes, terpenes, or oils in their leaves, twigs and stems
Strong odor when leaves are crushed
Sap that is gummy, resinous, and has a strong odor
Loose or papery bark
...While, generally, fire-resistant plants have:
Moist and supple leaves
Minimal dead wood and do not tend to accumulate dry/dead material within the plant
Low sap or resin materials
Sufficient water and nuturients to be healthy
Fire-resistant does not mean fire proof! Even fire-resistant plants that are not well maintained can burn. Be sure to keep all of your landscape plants healthy with appropriate watering and pruning
Maintenance is Critical. As with any fire-resistant landscaping, maintenance is critical. Deep watering, mulching, and the removal of deadwood and leaves help to maintain the overall health of the plant, thereby reducing the flammability of the overall landscape. Keep the following maintenance tips in mind when preparing your vegetation for wildfire:
fertilize as needed,
prune to remove dead material,
and remove dry leaves or weeds annually that accumulate between plant
Heavy shearing or pruning may promote a dense outer crown, resulting in less sunlight reaching the interior of the hedge and causing dieback of twigs. This dieback will create flammable material in the center of even healthy, well spaced shrubs and trees.