Fire resistant landscapes both use plants that have low flammability, and cite them strategically so as to reduce the amount of fuels (vegetation) that could ignite structures or carry flame across the landscape. In a 30-foot diameter around structures, plants that require more water are used and are watered regularly. 30-70 feet from a structure, more drought-resistant plants are used, and are watered regularly but appropriately to their needs. Well-hydrated plants take longer to ignite than plants with low moisture content. Shrubs and trees are widely spaced and don’t touch or hang over structures. Low growing plants are used around decks and under windows. Foundation shrubs are eliminated and low growing groundcover-type plants are used instead. Plants are not contiguous.
In urban areas, houses and other structures constitute the most flammable items rather than plants. However, using plants with low flammability, keeping them well hydrated, and maintaining the landscape free of dead grass and debris will help reduce flammable materials.
In larger landscapes, particularly those on slopes, it is vital to have enough plants for roots to hold soil. Native plants are best suited for this purpose. They can be spaced so they fill about 40-50 percent of the space. Deep-rooted shrubs like manzanitas, toyon, coffeeberry, redbud and California lilac should have branches thinned to open up the plants structure. Heading cuts cause plants to produce dense, twiggy growth. Lower branches can be removed. Plants that resprout from the base such as coyote brush, chamise, and coffeeberry, can be cut down every few years to keep plants vegetation young and lush. Maintain all plants free of dead leaves and debris.
Commonly used drought resistant (and deer resistant) plants like rosemary, lavender, rockroses, oleanders and ornamental grasses are more flammable than most native plants. The dense growth, accumulation of dead of dry leaves and stems, and the oils and resins contained in the plants render them highly flammable.
Mulches are still appropriate. Plants need soil fertility, and mulches with low flammability such as compost, composted woodchips or 2-3 inches of woodchips are beneficial to plants, help reduce weeds, retain soil moisture and protect the soil from rains. In fire-prone areas, use gravel, rock or pavers in a 30-foot diameter around structures. Compost can be used around each plant.