By Todd Veden, BCE, Compliance and Qualifying Manager for California, Terminix
Many home gardeners believe that certain plants repel landscape and household pests. In fact, a quick internet search reveals many articles about plants with pest repellent properties and suggestions that these plants can also reduce the need for pesticides in the garden.
It is true many plants have repellant properties and some insects will avoid certain varieties, but one cannot rely solely on plants to keep pests away. For example, it is said that borage is repellant to tomato hornworm and that dahlias are repellant to soil-borne nematodes. Unfortunately, the roots of tomatoes planted in soil infested with root knot nematode will be attacked even with dahlias planted nearby. The same would be true for the tomato hornworm; they may not like the taste of borage, but the tomato plants taste great and will be eaten if planted nearby.
Other common plants with repellant properties are in the sunflower family. Home gardeners know that marigolds and chrysanthemums are known for their insect repellant properties because they contain pyrethrum—a naturally occurring essential oil included in many common pesticides. However, to get the most benefit, the plant has to be ground up to release the oil.
Essential oils that have repellant properties are contained inside the plant. And while some pests may be repelled, to get the total effect the oils only become available when plants are processed by manufacturers. In fact, many of these oils make up the natural or green pesticide products family we see on the market today. Some common pesticides from naturally-occurring oils include:
Bottom line, certain plants may repel certain insects, but no single plant will repel all insects. A variety of these plants in the garden may reduce the incidence of many pests, but gardeners should also employ sound horticultural practices through varietal selection, good cultivation, proper irrigation and implementing IPM in their garden.