Cedar does repel termites, but the protection is limited and depends heavily on which part of the wood you’re talking about. The heartwood, the dense inner core of a cedar tree, contains natural chemicals that deter termite feeding and can even kill them. The sapwood, the lighter outer layer, offers far less protection. And in real-world conditions, cedar alone is not enough to prevent termite damage entirely.
How Cedar’s Natural Chemistry Works
Cedar heartwood contains a group of plant compounds called flavonoids that act as feeding deterrents. When termites encounter these chemicals, they avoid eating the wood. Two compounds in particular, taxifolin and catechin, are responsible for much of this effect. Taxifolin is the stronger of the two, and it concentrates heavily in the innermost heartwood. Catechin is found mostly in the sapwood, where it provides weaker protection.
This distribution matters. In lab tests on Atlas cedar, paper samples soaked with inner heartwood extracts were barely damaged by termites, while samples treated with sapwood extracts fared much worse. Termites exposed to inner heartwood extracts also had significantly lower survival rates. The termites didn’t just avoid the treated material; they starved rather than eat it, dying at roughly the same rate as termites given no food at all.
Cedar Slows Termites but Doesn’t Stop Them
Lab studies on the Formosan subterranean termite, one of the most destructive species worldwide, show that cedar cuts feeding rates roughly in half compared to other common lumber species. About 50% of termites died within three weeks when cedar was their only food source, a mortality rate significantly higher than for woods like pine or oak.
That sounds impressive, but there’s a critical caveat. In the field, termites don’t depend on a single wood source. They forage across large areas and can supplement their diet with other materials. Researchers who conducted the Formosan termite study noted that both redwood and cedar “have been severely damaged in the field,” even though termites performed poorly on them in controlled settings. Soil microorganisms can also break down cedar’s protective compounds over time, weakening the wood’s natural resistance.
Western red cedar carries an official durability rating of “termite resistant” in Australian timber classification systems, with an above-ground life expectancy of 15 to 40 years and an in-ground life expectancy of 15 to 25 years. That’s a strong rating, but “resistant” is not “immune.” It means cedar lasts longer than most untreated woods, not that termites will never touch it.
Cedar Mulch Is a Different Story
Many homeowners assume that spreading cedar mulch around a foundation will create a termite barrier. The reality is more complicated. While cedar heartwood resists termites, most commercial cedar mulch is a mix of heartwood, sapwood, bark, and other wood species. The protective chemicals are diluted or absent entirely in these blends.
In one university study, a utility mulch blend that included cedar (along with oak, cherry, pine, and camphor) was actually consumed by subterranean termites more than any other mulch tested, including plain pine sapwood. The cedar content wasn’t high enough to provide meaningful deterrence, and the mulch’s moisture created ideal conditions for termite activity.
That moisture factor is key. Subterranean termites need consistent access to water. Mulch of any type holds moisture against the soil surface and keeps it warm, which is exactly the environment termites thrive in. Mulch also provides a cellulose food source in direct contact with the ground. If you’re irrigating landscaping beds near your home’s foundation, mulch layers can become a welcome mat for termites regardless of the wood species involved.
Cedarwood Oil as a Treatment
Cedarwood essential oil has shown more consistent results than the raw wood in some applications. USDA researchers developed an emulsion combining cedarwood oil with modified starch that, when applied to pine lumber, made it resistant to both termite attack and wood-rot fungi. The treated pine also absorbed less water, reducing the moisture conditions termites need.
Researchers haven’t fully determined whether the oil works by making the wood unpalatable (causing termites to starve) or by poisoning them when they eat it. Either way, the oil’s concentrated chemistry appears to deliver the protective effect more reliably than simply using cedar lumber, where the natural compound levels vary from board to board and degrade over time with weathering and microbial activity.
What This Means in Practice
If you’re choosing lumber for a deck, fence, or raised garden bed, cedar heartwood is genuinely more termite resistant than most untreated softwoods. It’s a reasonable choice for above-ground projects where you want natural durability without chemical preservatives. But it shouldn’t be your only line of defense for structural components, especially anything in contact with soil.
For mulch, the species matters far less than placement. Keep any mulch at least six inches from your foundation, avoid piling it against siding or framing, and don’t assume cedar mulch creates a protective zone. It doesn’t. The moisture it retains can actually work against you.
Cedar’s reputation as a termite repellent is earned, but it’s best understood as a speed bump rather than a wall. Termites prefer other food sources when they have a choice. When cedar is the only option, many of them die. But given time, access to moisture, and alternative food nearby, termites can and do damage cedar in the real world.