All vegetation, naturally occurring and otherwise, is potential fuel for fire. There are no truly "fireproof" plant species. Under extreme fire conditions all plants will burn. Plant choice, spacing and maintenance are critical to defensible space landscaping. Where and how you plant can be more important than what species you use. However, given alternatives, choose plant species that tend to be more fire resistant.
In general, plants that are more resistant to wildfire have one or more of the following characteristics:
The following plants have been selected from Cooperative Extension Service information2 available from across the country and then cross checked with the plants that should do well in Tulsa County during periods of drought3. If your particular preference is not found in this list please refer to the ADDITIONAL INFORMATION section at the end of this article for LINKs to more complete lists.
Remember not all plants are equally fire resistant. They range from the cactii and succulents to the high water content herbaceous then the broader leaf vines and shrubs.(See Landscape plant characteristics )
The following plants, although drought tolerant, will still need some water to stay alive during extended drought. Trees and shrubs will need regular watering during their first year in the landscape to establish a good root system. The annuals and perennials listed will survive drought conditions but they will not produce new flowers.
Most drought tolerant plants need good drainage to prevent root rot. Soil drainage can be improved by "tilling in" organic matter and the use of raised beds.
For efficient water use, group plants with similar water and environmental needs into beds.
Drip irrigations systems can provide up to 95% water use efficiency compared to 50% for sprinkler systems during hot, windy days.
The use of approximately 3 inches of plant based mulch will greatly reduce soil surface evaporation and cool the plant's roots improving root growth and overall plant health.
Trees provide a large amount of available fuel for a fire and can be a significant source of fire brands if they do burn. Radiant heat from burning trees can ignite nearby shrubs, trees and structures.
The best species to plant generally are those already growing on or near the site. Others may be planted with careful selection and common sense.
Plant deciduous trees and avoid conifers. These species, even when planted in dense clumps, generally do not burn well, if at all. The greatest problem with these trees is the accumulation of dead leaves in the fall. Remove accumulations close to structures as soon as possible after leaf drop.
Carefully plan their placement. Do not plant trees near structures. Leave plenty of room between trees to allow for their growth. Spacing within the defensible space should be at least 10 feet between the edges of tree crowns. On steep ground, allow even more space between crowns. Plant smaller trees initially on a 20- to 25-foot spacing to allow for tree growth. At some point, you will have to thin your trees to retain proper spacing.
As the trees grow, prune branches to a height of 10 feet above the ground. Do not overprune the crowns. A good rule of thumb is to remove no more than one-third of the live crown of the tree when pruning. Prune existing trees as well as ones you planted.
Do not plant shrubs, vines or other type of "ladder fuel" beneath a tree. They can carry a relatively easy-to-control surface grass fire into tree crowns. Crown fires are difficult, sometimes impossible, to control. Limit the number of trees of this type within the defensible space. Mow the grass around such specimen trees.
Shrubs can add significantly to total fuel loading. Because of the woody material in their stems and branches, they are a potential source of fire brands. When carried in the smoke column ahead of the main fire, fire brands can rapidly spread the fire in a phenomenon known as "spotting."
But the primary concern with shrubs is that they are a "ladder fuel". They can carry a relatively easy-to-control surface grass fire into tree crowns. Crown fires are difficult, sometimes impossible, to control.
To reduce the fire-spreading potential of shrubs, plant only widely separated, low-growing, nonresinous varieties close to structures. Do not plant them directly beneath windows or vents or where they might spread under wooden decks. Do not plant shrubs under tree crowns or use them to screen propane tanks, firewood piles or other flammable materials. Plant shrubs individually, as specimens, or in small clumps apart from each other and away from any trees within the defensible space.
Mow grasses low around shrubs. Prune dead stems from shrubs annually. Remove the lower branches and suckers to raise the canopy away from possible surface fires.
The primary concern with climbers is that they are a "ladder fuel". They can carry a relatively easy-to-control surface grass fire into tree crowns.
To reduce the fire-spreading potential of climbers, plant only widely separated locations using non-combustible supports away from structures. Do not plant them directly beneath windows or vents or where they might spread under wooden decks. Do not plant climbers under tree crowns or use them to screen propane tanks, firewood piles or other flammable materials. Plant climbers individually, as specimens, or in small clumps apart from each other and away from any trees within the defensible space.
Mow grasses low around climbers. Prune dead stems from climbers annually. Remove the lower branches and suckers to raise the canopy away from possible surface fires.
Ground cover plants break up the monotony of grass and, provide a variety of textures and color and help reduce soil erosion. Consider ground cover plants for areas where access for mowing or other maintenance is difficult, on steep slopes and on hot, dry exposures.
Ground cover plants are usually low growing. They are succulent or have other fire-resistant characteristics. When planted in beds surrounded by walkways and paths, in raised beds or as part of a rock Garden, they become an effective barrier to fire spread. The ideal groundcover plant is one which will spread, forming a dense mat of roots and foliage that reduces soil erosion and excludes weeds.
Flowers provide color and brighten up the landscape from spring until fall.
The concern with flowers is the large amount of available fuel they can form. To reduce the fire hazard, plant flowers in widely separated beds within the defensible space. Do not plant them next to structures unless the beds are frequently watered and weeded and vegetation is promptly removed after the first hard frost. Use gravel walkways, rock retaining walls or irrigated grass areas mowed to a low height to isolate flower beds from each other and from other fuels.