Junipers, Arborvitae and Other High-Risk Shrubs Near Homes

Why are junipers so flammable?

MSU Extension's MontGuide Fire-Resistant Plants for Montana Landscapes uses junipers as its example of a highly flammable plant that should not be used as a foundation planting in the wildland-urban interface, because juniper foliage contains volatile oils and the beds around the plants accumulate a lot of old, dead material. That combines the two traits the guide says make plants burn: aromatic, resinous tissue and a buildup of dead, dry material.

Boulder County, Colorado's wildfire mitigation program describes the same thing in more detail: junipers are highly combustible because of their volatile oils, dense growth and retention of dead plant material; they collect dead leaves and trash; trapped needles and debris beneath them are highly susceptible to ember ignition; and they burn hot and fast, giving off large flames and abundant embers. It also notes that plants that were small and separate when planted have often grown together into a continuous wall of volatile vegetation.

Is arborvitae as risky as juniper?

Wildfire guidance treats them together. The City of Ashland, Oregon's fire-reluctant landscaping guidance lists arborvitae, juniper, cedar and cypress among the plants not to plant in an urban setting, adds that even dwarf varieties can be highly flammable, and recommends eliminating all junipers and arborvitae, regardless of location, in higher density housing areas. That is Oregon guidance rather than a Montana rule, but the reasoning applies anywhere.

Arborvitae adds a layout problem. It is usually planted as a tight hedge, often along a fence line or property line, and a hedge is a continuous fuel bed. The IBHS Wildfire Prepared Home checklist says continuous hedges or rows of shrubs, and continuous rows of trees or tree and hedge combinations, should be kept at least 10 feet from the home. Our guide to wood fences attached to a house covers why a hedge next to a fence is a particular concern.

Which other shrubs belong on the high-risk list?

Ashland's list also names pampas grass, bamboo, broom, sagebrush and rabbitbrush. Two of those matter in Montana for a second reason: Scotch broom is a Priority 1B noxious weed on the Montana Department of Agriculture's list (the version effective June 21, 2019), and should not be planted at all. Sagebrush and rabbitbrush are native here and have a place on open ground well away from buildings, just not against a wall.

Ashland's guidance extends further to any conifer, recommending that no coniferous tree or shrub be planted within 30 feet of structures, and the IBHS checklist removes all vegetation from the first 5 feet regardless of type. Dwarf pines and spruces in a foundation bed raise the same questions as juniper: resinous foliage and dead material collecting inside. MSU's WUI MontGuide makes a general point that applies to all of them: deciduous shrubs are often preferred over conifers near homes because of their higher moisture content and structure. Ornamental grasses are a separate case, covered in our ornamental grasses guide.

Do I have to remove every juniper on the property?

No. Location decides it. MSU's WUI MontGuide says coniferous trees and shrubs, it names juniper and fir, can remain if the distance between individual crowns, between groups, and between plants and other flammable materials is adequate, and that the distance should increase on steep slopes. A native Rocky Mountain juniper out in the open on a hillside 100 feet from the house is a very different thing from a creeping juniper bed against the foundation.

The Colorado State Forest Service's Home Ignition Zone guide is firmer about the low ones: it says common ground junipers should be removed whenever possible because they are highly flammable and tend to hold a layer of flammable material beneath them. A reasonable order of priority is: anything within 5 feet of the house, deck or a fence that touches the house first; hedges and groups within 30 feet next; isolated plants farther out last, with the dead material cleared from under them. Our defensible space zones guide explains the zone distances.

How do you remove a juniper or arborvitae?

Boulder County's guide gives the steps for homeowners: wear long sleeves and long pants, cut the plant back to the trunk, rake out all the debris underneath, then dig or pull smaller plants with shallow roots, or cut larger ones flush with grade or lower and remove what roots you can. It notes the plant should not grow back, and that the stump can be ground if you are careful that no power or water lines will be affected.

Two practical notes from our side. Raking out the debris layer matters as much as cutting the plant, because the dead material underneath is what catches embers. And large arborvitae hedges and old spreading junipers are often bigger jobs than they look: the root mass, irrigation lines run through the bed, and the sheer volume of material add up. The cut material should be chipped or hauled rather than piled near the house; our slash disposal guide covers the options, and stump grinding takes care of what is left at grade.

When is the best time to take junipers and hedges out?

Fall through early spring, for the same reasons as other fuel reduction work. Dense evergreen hedges often hold bird nests, and spring and early summer work has to stop if active nests are found in the material being cut. Hot, dry, windy days in fire season are the wrong time to run saws and grinders in dry vegetation next to a house. Taking a hedge out in autumn also leaves the winter to plan the replacement planting and the spring to plant it.

If you are doing the work in stages, take out the plants against the house first. They carry the most risk, and removing them is usually the simplest part of the job. Our seasonal fire calendar covers timing for the rest of the work.

Can I keep a juniper if I prune it and water it?

Pruning and watering help farther from the house; they do not make a juniper suitable next to it. Boulder County's guide says no plant is fireproof and all vegetation should be kept at least 5 feet from your home or in noncombustible pots, and the IBHS checklist makes no exception for irrigated or fire-resistant plants in that zone.

For a plant you keep in the outer zones, the useful maintenance is removing the dead interior material every year, keeping the skirt lifted off the ground, keeping it separate from other shrubs and from tree canopies (CSFS recommends keeping shrubs at least 10 feet from the edge of tree branches) and not letting needles or mulch pile up beneath it.

What should I plant where the junipers were?

Within 5 feet of the house, nothing: a gravel, river rock or paver band, as described in our first five feet guide. Beyond that, low deciduous shrubs and perennials from MSU's fire-resistant list for Montana, which includes shrubby cinquefoil, currants, redosier dogwood, chokecherry, mock orange and lilac among shrubs, and kinnikinnick, creeping mahonia, yarrow and blanket flower as low groundcovers. Our fire-resistant plants guide covers the full list, spacing rules and the noxious weed exceptions.

If the arborvitae was there for privacy, a noncombustible screen or a fence with a metal section near the house can take over that job, with a looser planting of deciduous shrubs farther out. Kinnikinnick and creeping mahonia are evergreen groundcovers on MSU's list, which helps if the attraction of juniper was year-round green.

Shrub removal and replanting is often the most visible change in a defensible space plan. This guide is part of our Montana Wildfire & Defensible Space Guide. HJ Property Care & Tree Service removes junipers, arborvitae hedges and overgrown shrubs, grinds stumps, and replants through landscaping and design, alongside the tree work in fire mitigation, across Missoula County and the Bitterroot Valley. Call HJ Property Care & Tree Service at (406) 215-7319 or request a free estimate and we will walk the property with you.

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