Cedar chests repel moths. Adding pencil shavings to potted plants repels or kills insect pests, such as ants, carpet beetles, cockroaches, fleas, mosquitos, moths, spiders, and termites. At least, that’s what they say.
Can we really use cedar as an insect repellent? It sounds (and smells) so nice…
Let’s start by learning a little more about what we mean when we use the word cedar.
Cedar is a conifer. The word ‘cedar’ refers to any of five Cedrus trees, all of which produce oils said to repel moths whose larvae eat fabrics, such as wool. These are ‘true cedars’, none of which are native to North America. Other trees lumped together with Cedrus are the Thuja, or cypress trees, three of which are native, and a few juniper trees. Cedar, cypress, and some junipers do contain chemicals, known as terpenoids, which are used to protect themselves against insect pests. The terpenoids used by cedar and cypress are not the same, however. Cedars use terpenoids called sesquiterpene hydrocarbons, while cypress and juniper use something called thujone. Thujone is also found in common sage, some mint species, mugwort, oregano, tansy, and wormwood. In both cases, some insects are repelled while others are not.
Insects and cedarwood oil
Your grandmother was right about her cedarwood hope chest - it really does repel clothes-eating moths. It does nothing, however, against fleas, mosquitos, spiders, and most ants. In its defense, if you have ordorous or Argentine ants, cedarwood oil will help keep them away. It will also repel or kill carpet beetles, cockroaches, and termites, none of which are a threat to your plants.
Dangers of cedarwood
Before you jump on the cedarwood oil bandwagon, however, you need to know that there is a downside. Research has shown that, while exposure to cedar wood oils can interrupt the reproductive and developmental cycles of peanut trash bugs, Indian meal moths, and forage mites, prolonged exposure to these oils increases your chances of getting cancer.
Strangely enough, European turnip moth larvae love eating cedar. Isn’t life weird?
You can grow a surprising amount of food in your own yard. Ask me how!
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