How to Use Companion Plants to Repel Harmful Insects in Your Garden

Plant diversity helps maintain the beneficial insect population.

Plants interact biochemically with each other, with the soil and with insects. Companion planting is a practice that is part ancient wisdom and part modern science that takes into account these chemical interactions and their effects. Marigolds exude thiophenes that destroy harmful soil nematode worms. Chives and cilantro repel aphids. Comfrey acts as a trap plant for slugs. Chamomile attracts beneficial hover flies. Dill and coriander release chemicals that drive away spider mites. Home gardeners maintain balance between harmful insects, which are less than 1 percent of insects, and beneficial insects by using companion planting techniques.

Things You'll Need

• Companion plant lists
• Local native plant nursery
• Garden journal

Instructions

1. Interplant strongly fragranced herbs throughout the garden. Strong scents confuse harmful insects looking for host plants to feed on. Basil repels flies, mosquitoes and thrips. Catnip mint drives away squash bugs and flea beetles. Garlic under peach trees drive away borer insects. Hyssop attracts bees to the garden and thwarts the cabbage moth.

2. Sow plants that attract beneficial insects that feed on harmful insects. Ground beetles, praying mantids, lady bugs, pirate bugs and hover flies are beneficial insects attracted by marigolds, nasturtiums, sage, sweet alyssum, geranium, goldenrod, hydrangea and yarrow. A wide diversity of plants ensures a diverse population of beneficial insects.

3. Grow native plants. Native vegetation is biochemically compatible with local beneficial insects, soil and weather conditions. Local native plant nurseries often offer education online and in their nurseries about companion planting with native plants.

4. Observe your plantings carefully. Write down combinations that improved pest control and growth enhancement. Not all beneficial companion pairings are recorded in the scientific literature. Local environmental conditions, native plants and wildlife may create distinctive companion plant combinations.

Tips & Warnings

• Nurse-cropping is the term used to describe plants that provide protection for surrounding plants. Tall flowers such as sunflowers and corn act as nurse plants to small, nearby plants like lettuce.

• Collards draw the diamond back moth away from cabbage.

• Allow some vegetable plants to go to seed to attract hover flies and parasitic wasps, which are beneficial to gardens.

• Check with local native plant nurseries or the Lady Bird Johnson Wildflower Center for a list of invasive plants. Some plants recommended for companion planting are invasive in many regions of the country.

References

• Cornell University Extension; Companion Planting; Robert Beyfuss, et al.; Winter 1994
• National Sustainable Agricultural Information Service; Companion Planting; George Kuepper, et al.; 2001
• Golden Harvest Organics: Companion Planting

Resources

• Lady Bird Johnson Willdflower Center: Invasive Plants