Recent research suggests that the scent of oriental red cedar, also known as juniper, is effective in repelling moths.
Cedar-lined chests and closets have long been used for storing clothes out of season for a long time, in the belief that cedar will prevent moths from destroying clothes. The damage that moths do to natural fibers is not caused by the moth itself, but by the larvae that hatch from the eggs the moth lays. Cedar has a strong smell, which can hide the smell of wool, but some forms can also kill larvae over time.
Some people use a cedar chest to store moth-sensitive material.
The strong scent of cedar is believed to mask the scent of wool, effectively hiding it from the moth that seeks a home for its eggs. That is, it does not repel the moths, but rather camouflages the moth’s natural target. If masking the scent does indeed deter moths, then any masking scent would work too, and people have packed old clothes with sprigs of lavender, tansy, and rosemary stuffed into them for literally centuries.
If the odor inhibitor works — and there’s only anecdotal evidence that it does — it only works on the egg-laying moth. Packing clothes that already contain moth eggs will result in a closet full of rotting wool. As larvae are repelled by strong light, shaking out and hanging clothes in the sun for a few hours before folding for storage should ensure that what is being stored is free of larvae.
Cedar camouflages the moth’s natural target rather than actually repelling the moths.
Mothballs have been used to destroy emerging larvae, but this method is less popular than before. The smell that mothballs leave on clothes is reason enough to avoid using them, but another deterrent must be the toxins they contain. These chemicals slowly evaporate, creating a toxic vapor that kills the moth larvae but is also dangerous for people and pets.
A report from the University of California at Davis suggests that one type of cedar, eastern red cedar (which is actually a juniper tree), kills moth larvae over time. The wood contains an aromatic oil that, in sufficient concentration, as in an airtight cupboard, kills small moth larvae. If there is a lot of air circulation, such as in a closet, the concentration of the vapors will remain insufficient to kill the larvae, although the smell may deter adult moths.
Whether other junipers — or juniper essential oil, which is otherwise made from juniper, and from the berries, not the wood — will protect clothing from moths, has not been determined. Even eastern red cedar is only effective against moth larvae for a few years, after which the aromatic oil has evaporated. The presence of a pleasant aroma of cedar in grandma’s old hop breast is no proof that the box will protect the wool from moth chewing.