Which Plants Repel Insects?

By Dr. Killigan
Which Plants Repel Insects?

"The brisk air enveloped me. I scanned the horizon, yearning for the day’s dawn. Stars, light years away, were my only companions. Sudden waves of violent wind lapped at my face and I turned away. In turning, I heard it. Miles away, my pious chocolate Labrador pulled at his leash, bound only by the strength of his leather collar. I could sense his hunger to find me. My pant legs, cloaked with wet earth. My muck boots, left to become part of the brown rich dirt in which they lay. He knew I needed help. I closed my eyes and could see his pulsating pull at the collar and hear his ceaseless barking that would wake the neighbors and bring me home. I lay on the cold thick earth waiting, listening to my own heartbeat and feeling the rhythmic throb of my fractured ankle."

I read the journal entry above and remembered that glorious spring evening when I had left my home, on foot, in search of wild allium plants, particularly the giant variation. While carefully maneuvering the rocky terrain on which I was walking, my foot had lodged between two seemingly small rather pleasant looking rocks. When I was finally able to pull it free, I found that my ankle was swelling, potentially fractured, and no longer able to assist me on my journey.

After hearing the effervescent barks of my lab, my heart rate had slowed. Less blood was pumped to my brain. The world went very dark. Wet, slobbery kisses woke me. I heard the quiet whisper of voices. The sun had risen. The violent wind was no longer. I felt bliss. I would somehow make it home this day and swore to carry on my search for wild alliums once my ankle had healed. 

I had heard that plants in allium family repel aphids and wanted to experiment with these varieties myself, especially because they had been used as a natural insecticide throughout indigenous history.

How Do Plants Repel Insects?

Certain plants and herbs repel insects through tiny balls of essential oils, or globules, that are naturally produced on plants' leaves. For example, if you rub the leaf of a lavender plant between your fingers, some of the plant’s essence (or essential oil) will be released and you’ll be able to smell it on your fingertips. The insect-repelling qualities of many plants and herbs are released when the foliage is bruised or moving about, allowing the essential oils to distribute and thus prove themselves as highly beneficial against warding off some insects. High temperatures can cause the globules to become volatile and evaporate the essential oils. When these herbs are dried, they also repel insects.

Plants That Repel Aphids (Primarily on Roses)

With its cluster of small dramatic purple, blue, pink, or yellow florets, allium—a genus of wildly decorative flowering plants—includes chives, garlic, leeks, and shallots. It is regarded as a broad spectrum insect repellent, emitting a sulfur-onion odor that masks the smell of other plants, but is undetectable to humans. Above ground, it is an excellent repellent against aphids and also wards off mosquitoes, cabbage worms, and slugs. Underground, it is a fantastic deterrent against pests such as grubs and nematodes.

Plant alliums a foot apart from your rose bushes, giving each its opportunity to flourish. Choose multiple varieties of alliums that will bloom at various times throughout the summer. Make sure to include either the gladiator allium or the allium giganteum, which will bloom in late spring to early summer.

Allium plant care: These bulbs need to be planted in well-drained soil in the fall, are generally winter hardy in zones 3-8, and prefer full sun.

Plants That Repel Mosquitoes (and Spiders and Flies)

Basil plants are toxic to mosquito larvae and can actually kill them before they hatch. If planted strategically—near standing water—this plant can even deter mosquitoes from laying eggs. More specifically, basil leaves have four charged compounds—estragole, citronellal, limonene, and nerolidol—that can deter mosquitoes.

 

Basil plant repels insects
To keep mosquitoes, moths, and flies from entering your home, pot fresh basil plants and place them near each of your doors. Flies detest the pungent, sharp scent and volatile oil of the basil leaves. Basil plants are also highly effective against flea beetles and the cabbage webworm.

 

To keep mosquitoes and other pests directly off of you, while working in your garden, crush a few leaves and rub them on your skin, as this will release their essential oils.

Basil plant care: Basil loves constant heat, a lot of sunlight, rich soil, plentiful water, and lots of space for its roots to grow, though it can also grow in partial shade, not-so-rich soil, and can cope with little water. (These not-ideal conditions will change your basil’s flavor, which isn’t brilliant if you’re planning to make pesto with it, which I hope you are). Make sure to trim your basil plants back to keep them healthy and bushy, don’t let them sit in wet compost, and harvest leaves by pinching them off, rather than snipping them with scissors, as this will promote fresh, new growth.

Lemongrass and citronella grass, two beautiful grassy plants, have citronella oil contained within their leaves. Citronella oil is one of the best-known alternatives to synthetic repellents like DEET (which is neurotoxic and has been detected in groundwater) and has been touted as one of the best plants for repelling the impact of and from mosquitoes.

In addition to warding off mosquitoes, these grasses are also fantastic at keeping spiders at bay, as citronella oil is rich in acids that extend a distinct smell to the grass. Spiders detest this smell. For maximum spider-warding results, plant it near your window panes, your balcony, or wherever spiders and their webbing frequent your home.

Lemongrass and citronella grass plant care: This grass is hardy as a perennial only in South Florida (USDA Plant Hardiness Zone 10), but can be grown as an annual everywhere else or potted (and brought indoors during the cooler months). If planted as an annual, allow adequate space, as citronella grass can grow quite large, and plant in an area with filtered sunlight. Water this plant frequently. These grasses make an excellent mosquito filtering screen and have a refreshing odor.

Please be mindful that the leaves of these plants are thin and sharp and must be handled with care. To protect yourself from minor skin cuts, you may want to wear gloves when trimming or harvesting this grass. 

Plants That Repel Flies (and Mosquitoes and Spiders)

Lavender plant repels insects

Lavender contains a non-toxic compound called linalool, which is highly effective at repelling not only flies, but also moths, mosquitoes, beetles, ticks, and fleas. Other plants that contain linalool, including basil, oregano, thyme, and mint, also have insect repelling qualities. However, due to its higher concentration of linalool, lavender is commonly considered as the most effective of these at repelling flies. The reason that insects keep their distance from this herb is because the linalool overloads their sensitive olfactory organs, much in the same manner as DEET.

Bonus: Lavender also deters rabbits from munching on your garden plants. 

Perhaps you recall the scene from A Good Life when Russell Crowe as the main character is staying at his uncle’s estate and notices a small box of dried lavender on the windowsill and, without thought, tosses it out the window. Well, little did he know that that lavender was what was keeping the scorpions, a type of arachnid, from coming through the open window at night. Lavender deters arachnids, too.

Lavender plant care: Lavender thrives on hot, dry, rocky, or sandy soil and is hardy in zones 5-10. This plant needs full sun. Give your lavender plant room to grow to combat humidity and, if you’re planting in the ground, make sure to add draining to combat soil saturation. Prune lavender straight after flowering to promote new growth.

Other Ways to Repel Pests

If you have a small yard or your budget doesn’t include a vast array of plants, I recommend the Insect Buster, filled with diatomaceous earth (DE) or another non-toxic pest control power. Simply fill the Insect Buster with food-grade diatomaceous earth (which must be purchased separately) and disperse a thin layer around the perimeter of your property. For additional protection, you may also distribute a layer around the perimeter of your home, your garden, or your patio area where you’re hoping to keep pest traffic to a minimum. 

To best spread the powder, use the shake and squeeze method and make sure to include the area under your porch. Due to crawl space, applying the powder under your porch may be difficult. In this instance, use the included extension rod to spray as far into this space as you are able.

Diatomaceous earth is a fine powder that is made from the fossilized remains of diatoms, a type of algae. It It has a hard shell, is high in silica, is very sharp, (although it is so find that it won’t do damage to your skin) and is effective against any insect with an exoskeleton, including wasps, fleas, mites, lice, ants, millipedes, earwigs, cockroaches, silverfish, bed bugs, crickets, centipedes, pill bugs, sow bugs, most beetles, fungus gnat larvae, and some grubs. (In fact, DE has many uses).

Final Word on Plants That Repel Insects

Have you used other plants around your home to repel insects? Have you had success with your efforts? It would be a pleasure to hear of your planting and insect-repelling wisdom.

I am now up and walking around; my troubled ankle is completely healed. But, I still enjoy a good recommendation from a reader.


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