Cedar for Silverfish: How Cedar Wood and Oil Repel Pests

Cedar has been used as a natural insect repellent for centuries. Cedar chests for storing woolens, cedar-lined closets, and cedar blocks in drawers are time-honored traditions rooted in real insect-repellent properties. Here is how cedar works against silverfish and how to use it effectively.

How Cedar Repels Silverfish

Cedar wood and cedar oil contain several aromatic compounds, including cedrol, thujone, and cedrene, that are responsible for its distinctive scent and insect-repellent properties.

These compounds work in multiple ways:

• Repellent effect: The strong aromatic compounds deter insects from entering cedar-treated areas.
• Mild toxicity: At high concentrations, cedar oil compounds can be toxic to small insects, disrupting their respiratory system and nervous system.
• Desiccating effect: Cedar oil can contribute to moisture loss in insects that come into direct contact with concentrated applications.

Cedar is particularly well-documented as a moth repellent, and its effectiveness against silverfish is supported by similar mechanisms, though less extensively studied.

Forms of Cedar for Silverfish Control

Cedar Blocks and Rings

Solid cedar blocks, rings, and balls are widely available at home goods stores. They release their aromatic compounds slowly over time.

Where to use:

• Hang cedar rings on closet rods
• Place cedar blocks on closet shelves and in drawers
• Position blocks behind stored books and in storage boxes
• Put blocks in shoe storage areas

Maintenance: Sand the surface of cedar blocks lightly every few months to expose fresh wood and renew the scent. Alternatively, add a few drops of cedar essential oil to refresh them.

Cedar Chips and Shavings

Cedar chips provide more surface area than solid blocks, releasing aromatic compounds more quickly.

How to use:

• Fill small fabric sachets with cedar chips and place them in drawers, storage boxes, and on shelves.
• Scatter chips in basement storage areas (away from moisture).
• Place chips in garment bags with stored clothing.

Cedar Essential Oil

Cedar essential oil provides the most concentrated source of cedar's active compounds.

Application methods:

• Add 10–15 drops to a spray bottle with water and spray along baseboards and in closets.
• Place a few drops on cotton balls and position in silverfish-prone areas.
• Add drops to a diffuser in affected rooms.
• Refresh dried-out cedar blocks by applying a few drops directly to the wood.

Cedar-Lined Closets and Chests

A cedar-lined closet or cedar chest provides continuous, passive repellent protection for stored items. While the initial investment is higher, cedar lining lasts for years and protects clothing and fabrics from both silverfish and moths.

If you cannot line an entire closet, cedar panels or planks can be attached to closet walls or the inside of storage trunks.

Effectiveness Assessment

Strengths

• Long track record as an insect repellent
• Non-toxic and safe for use around people and pets
• Pleasant, natural scent
• Multiple product forms available
• Durable — solid cedar products last for years
• Dual protection against both silverfish and clothes moths

Limitations

• Primarily a repellent — does not kill established silverfish populations
• Scent diminishes over time (blocks need sanding or refreshing)
• Does not affect silverfish eggs
• Cannot reach silverfish in wall voids or other inaccessible harborage areas
• Effectiveness decreases as the aromatic compounds dissipate

Best Practices

For maximum benefit from cedar:

1. Use in enclosed spaces: Cedar is most effective in confined areas (drawers, closets, storage boxes) where the scent can concentrate. In open rooms, the scent dissipates too quickly.
2. Refresh regularly: Sand blocks or add oil every two to three months.
3. Combine with other repellents: Use cedar alongside lavender and cinnamon for broader repellent coverage.
4. Pair with effective treatments: Use diatomaceous earth, boric acid, and humidity control as your primary control methods, with cedar as a supplementary deterrent.
5. Monitor with traps: Use sticky traps to assess whether cedar is reducing silverfish activity in treated areas.

For a complete silverfish control strategy, see our guide on how to get rid of silverfish. For comprehensive information, visit the complete guide to silverfish.

Expert Insight

"I have tested cedar products in many residential settings over my 15 years in IPM," says Sarah Mitchell, BCE. "Fresh cedar blocks and shavings do show some repellent effect against silverfish in enclosed spaces like closets and drawers. However, the volatile oils dissipate within a few months, and I have never seen cedar alone resolve an established infestation. I recommend it as a supplementary measure alongside humidity control."

Main Causes

Silverfish establish indoors wherever sustained high humidity and accessible food sources coincide. Relative humidity above 75 percent is their primary requirement, occurring most consistently in basements, crawl spaces, bathrooms, and poorly ventilated closets - exactly where cedar storage products are most commonly used. Common moisture drivers include plumbing leaks, condensation on cold pipes, and inadequate exhaust ventilation. Food sources that draw silverfish include cellulose in paper and cardboard, starch in wallpaper paste and book bindings, and natural fiber fabrics such as cotton and linen. Cluttered storage with abundant cardboard boxes provides both food and undisturbed harborage, making closets and storage rooms high-risk locations regardless of cedar placement.

How to Identify

Silverfish are 1/2 to 3/4 inch long with a tapered body covered in metallic silver-gray scales, three tail filaments, and two long antennae. Their rapid lateral movement is distinctive. In areas where cedar products are being used, confirm silverfish activity through indirect evidence: irregular surface scraping on book covers, wallpaper edges, and fabric; small black droppings resembling ground pepper in closet corners and on shelf surfaces; and shed exoskeletons in undisturbed storage areas. Sticky traps placed in active zones provide a clearer picture of population size and confirm whether cedar treatment is reducing captures over time relative to a pre-treatment baseline.

Risk and Severity

Silverfish pose no direct health risk - they do not bite, sting, or transmit disease. The primary concern is material damage. They feed on paper, book bindings, starched fabric, and wallpaper paste, with losses that can be irreversible for rare books, historical documents, and heirloom textiles. Shed scales and droppings contain tropomyosin, which can aggravate symptoms in people with dust allergies or asthma when particles accumulate in enclosed storage areas. Cedar repellents slow silverfish activity in treated spaces but do not eliminate populations nesting in wall voids or damp foundation areas, and do not address the moisture conditions that sustain infestations long-term.

Prevention

Cedar works best as a supplementary layer within a structured prevention plan. Maintain indoor humidity below 50 percent using a dehumidifier - this is the single most impactful measure. Store clothing and textiles in cedar-lined chests or sealed plastic bins rather than open cardboard boxes. Place fresh cedar blocks or sachets in closets and drawers, refreshing or sanding them every two to three months as the scent diminishes. Seal cracks around baseboards and pipe penetrations to eliminate harborage. Fix plumbing leaks and ensure exhaust fans vent moisture outside. Combine cedar with sticky traps and periodic inspection to detect resurgence before populations rebuild to problem levels.

Solutions and Actions

Silverfish respond to a combined moisture-control and targeted-treatment program. Address the underlying humidity problem first by running a dehumidifier in basements and storage areas to keep relative humidity below fifty percent, repairing slow leaks, improving bathroom ventilation, and resolving condensation on cold-water pipes. Apply diatomaceous earth or boric acid dust in cracks and crevices, behind baseboards, under bath fixtures, and around utility penetrations — these slow-acting desiccants work as silverfish move through treated areas. Place sticky monitor traps in active rooms to verify the population is declining. Inspect cardboard storage, dispose of damaged boxes, and switch to plastic storage bins for paper goods, books, and clothing. Treatment without humidity control consistently fails.

Frequently Asked Questions

How long does cedar remain effective against silverfish?

Fresh cedar products release aromatic oils that may repel silverfish, but these oils typically diminish within three to six months. Sanding the surface of cedar blocks can temporarily restore their scent. For sustained protection, cedar should be replaced regularly or combined with other control methods.

Is cedar oil more effective than cedar blocks?

Cedar oil can provide a more concentrated repellent effect than solid cedar blocks. However, the oil evaporates relatively quickly and needs to be reapplied. Neither form has been scientifically proven to eliminate silverfish infestations on its own.

Can I use cedar in closets to protect clothes from silverfish?

Cedar closet liners, blocks, and hangers can help deter silverfish from entering closets. However, for effective clothing protection, combine cedar with low humidity, sealed storage for vulnerable items, and regular inspection. Cedar alone may not prevent a determined silverfish population from feeding on stored clothing.

Where does cedar help most against silverfish?

Cedar works best where its scent can concentrate: drawers, garment bags, cedar chests, storage boxes, and small closets. It is weakest in open rooms or damp basements where the scent dissipates. Pair it with sealed storage, low humidity, and traps to see whether activity drops.

Sources and Further Reading

• NPMA — Silverfish Overview
• Purdue Extension — Silverfish Control
• NC State Extension — Silverfish and Firebrats