Wildfire-Resistant Landscape Plants for Michigan (E2948)
Most Michigan residents are surprised to learn that Michigan experiences 8,000 to 10,000 wildland fires each year. It is estimated that forest fires, brush fires and grass fires destroy or damage 100 to 200 homes, barns and outbuildings annually.
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Most Michigan residents are surprised to learn that Michigan experiences 8,000 to 10,000 wildland fires each year. It is estimated that forest fires, brush fires and grass fires destroy or damage 100 to 200 homes, barns and outbuildings annually. When wildfires occur, the right landscape plants, especially fire-resistant plants, can help increase the chance that a home will survive. Allowing wildland vegetation to grow too close to a structure or placing flammable landscape plants near a home or other structure increases the chance that the structure will ignite.
Wildfires move along the ground or through brush or forests by igniting the vegetation or fuels ahead. Figure 1 shows how coniferous trees can ignite and “torch” during a wildfire. If these trees were growing next to a house or building, the structure would surely ignite. This is why it is important to select fire-resistant plants when landscaping around the home.
How Homes and Other Structures Ignite During a Wildfire
Studies have shown that homes and other structures can be ignited by a wildfire in three ways. The first of these is through direct contact, otherwise referred to as “convection.” Direct contact of flames to combustible wood decks and siding may easily set the building on fire. When combustible trees and shrubs are touching the home or growing very close to it, they can ignite and bring the home into direct contact with the flames.
A second way that wildfires cause buildings to burn is through radiant heat. This refers to the intense heat that is produced by burning vegetation. If forest fuels or landscape plants grow too close to the structure, the structure can be set on fire by radiant heat, even though the flames may not actually touch the structure. The primary way to protect your home from convection or radiant heat is by eliminating flammable vegetation near the structure. This vegetation will serve as fuel; without this fuel, the fire cannot jump to the structure.
The third and a very common cause of structures catching fire during a wildfire is firebrands. Firebrands are floating embers that are still burning or glowing when they land. Firebrands have been known to travel up to a mile downwind from an intense wildfire. In large wildfires, firebrands are a concern because they will start new spot fires well ahead of the main fire. Experience has shown that firebrands from a wildfire or burning landscape plant may also land on or under decks, in leaves that have collected behind landscape plants, in eave troughs where leaves and vegetative litter have become trapped, or directly on wood shingles. Firebrands that land in or on these flammable materials can ignite the fuels and destroy the building.
One way to help prevent homes and other structures from catching fire is to eliminate these ignition points by creating defensible space around them. This can be achieved, in part, through proper landscape plant selection and placement. Plants that do not burn easily are less likely to set a structure on fire.
Selecting Landscape Plants
Given the right conditions, any plant will burn. However, because of the composition of the foliage or moisture content in the leaves, certain plant types are less likely to catch fire and are therefore termed “fire-resistant.” Fire-resistant landscape plants should be your first choice if you live in a rural or urban-wildland interface area where wildfire is a possible threat.
Even before homeowners consider the right trees, shrubs and ground covers, other landscape issues should be considered. For example, a dry lawn can burn and carry a fire to the home or other structure. Lawns should be watered, and dead lawn litter should be raked and either removed from the property or composted. A green lawn will not carry a fire.
In nature, some plants ignite more quickly than others and burn with more intensity. For example, plants that contain resins — such as conifers, certain shrubs and dune grass — ignite easily and create very hot fires that radiate much heat. Firefighters at a wildfire in dune grass near Shelby, Michigan, in 2005 (Figure 2) reported flames as high as 20 feet. Two homes were destroyed in the fire, and a number of others had fire damage.
Other species, such as junipers, tend to retain dead foliage in the branches, which also serves as an ignition point for firebrands. Other conifers that have branches growing close to the ground can provide “ladder fuels” for a surface fire to climb into the tree canopy.
Wildfire-resistant Plant Species
The species of trees, shrubs and ground covers in Table 1 are considered wildfire-resistant and are recommended for Michigan’s climate. Remember that any plant may burn if the plant tissue becomes very dry and if the vegetation is exposed to intense heat for a period of time.
Your local lawn and garden centers may sell or have access to many of the fire-resistant plant species mentioned in this publication. An excellent source of information on local landscape dealers is the MSU Extension office in your county. Both the landscape dealer and the Extension agent can provide information on growing characteristics, required growing conditions, winter hardiness and planting sites required for various plants.
Locating Shrubs and Trees in the Landscape
Where you locate ornamental plants is just as important as the species you select. Spacing between trees and shrubs is important so that fire cannot jump from a plant to the home, nor from one plant to another and finally to your home. Spacing depends on the species selected. It is also important to remember that the distance between two plants will decrease as they grow larger. Space plants according to their mature size, not their size at planting. The spruce trees in Figure 3 were planted too close to the home and are now a threat because of direct flames and radiant heat, should the trees ignite.
When creating defensible space in the yard, provide a minimum of 3 feet of clearance between the structure and landscape plants. Non-flammable landscape material such as limestone, marble chips or even mineral soil can be used in this area. Avoid using organic mulch, peat or wood chips within the 3-foot barrier. These materials can ignite when dry.
Leave at least 30 feet of defensible space between the structure and solid stands of wildland vegetation. Studies in the western states have shown that 85 to 90 percent of homes with 30 to 50 feet of defensible space and fire-resistant roofing materials survived major wildfires. Ornamental landscape plants may be placed within the defensible space, but it is important to maintain 10 to 16 feet of space between the crowns of the plants.
Houses and structures built at the crest of a hill should have a minimum of 60 feet of defensible space on the downhill side of the structure, because a fire traveling uphill will be more intense and radiate more heat than a wildfire moving on level ground. Liquid propane tanks, stacks of firewood and other fuels should be located outside the 30- or 60-foot perimeter.
The term “ladder fuels” describes low-hanging branches and limbs that could catch fire from a wildfire moving across the ground. If the tree is combustible, such as a spruce tree, the fire will ignite the lower leaves and move upward. Should this happen, the radiant heat given off could set a nearby house or other structure on fire. Remove limbs and branches of ornamental landscape trees within 6 to 8 feet of the ground so that fire cannot move from the ground to the lower branches of the tree.
Planting Ornamental Trees and Shrubs
When planting any tree or shrub, it is important to match the species with the conditions in the planting site. Some species may grow better in sandy soils than in heavy clay soils. Some will do better than others in poorly drained areas. Other species may do better in the sun than in the shade. This information is often included on a tag attached to the tree or shrub at the garden center. If there is no tag, ask an informed employee about the preferred environment before purchasing. Again, your local Extension office will likely have this information as well.
At planting time, dig a hole that is larger than the root ball. This will provide an area of soft soil for new feeder roots to expand into and take hold. Fall or spring planting depends on the species selected. Avoid planting during the midsummer months because of high temperatures and sparse rainfall. To obtain more information on planting landscape plants, obtain a copy of Extension bulletin E-2941, A Guide for the Selection and Use of Plants in the Landscape, from your county Extension office.
Maintaining the Yard and Shrubbery
If the landscape is not maintained properly, a wildfire can move across the yard and ignite a home or other structure. To decrease this possibility, keep your lawn mowed and watered. A green lawn is unlikely to catch fire and will typically serve as a protective barrier around the home. On the other hand, a yard that is managed in natural vegetation or a lawn that has become very dry could allow a wildfire to move across it and pose a danger of the wildfire igniting a deck or wood siding, and then the home. The home and garage shown in Figure 4 were damaged because tall grass was allowed to grow too close to the structures.
It is also important to provide adequate water for newly planted trees and shrubs. Once these plants have grown and have established extensive root systems, they should usually be able to absorb necessary water from the soil, and nutrients from the soil and from lawn fertilizers. Ornamental plants may or may not need special fertilization.
This can be determined by a soil test, which is available through your local Extension office. For more information, pick up a copy of North Central Region publication 356, Fertilizing Garden & Landscape Plants & Lawns, from your county Extension office.
Each year in Michigan, wildfires damage or destroy homes and other structures. A firewise home includes adequate defensible space, fireresistant building materials, and eave troughs and spaces around and under the base of the home void of leaves. Firewise homeowners also place other fuels, such as LP tanks and firewood stacks, at a safe distance from the home. Adding fireresistant plants and pruning trees can greatly increase the chances that a home or other strucures will still be standing after a wildfire passes, while also providing the esthetics that the homeowner desires (Figure 5).
For more information on Michigan wildfires and protecting your home and family, pick up copies of Extension bulletins E-2831, Protect Your Michigan Home from Wildfire, and E-2882, Understanding Wildfire Behavior in Michigan, from your county Extension office.