Organic Insect Repellent for Plants

Caterpillars and other pests might destroy your plants.

Insect pests can become quite a nuisance when they start eating your plants. If you're not wanting to use harmful, toxic synthetic insecticides, you have several options that are natural and organic. "Natural" and "organic" do not necessarily mean safe, though, and should be used with caution.

Companion Planting

Companion planting is the act of planting certain plants near each other for beneficial effects. Many times, these benefits include repelling insect pests from their neighbor plants and themselves. Sweet basil is an example of a companion plant for tomatoes. In addition to promoting growth and better flavor for the tomatoes, the basil also acts as a repellent to flies and mosquitoes. Allium is a companion to several plants including raspberries and roses. It repels mice, peach borers and Japanese beetles, among other pests. Marigolds prevent and deter a long list of insects and nematodes. They are ideal for protecting strawberries, various bulbs and roses.

Insecticidal Soaps

Although insecticidal soaps are not a repellent, they are a natural, organic insecticide for plants. Much like the soaps you use on your body, insecticidal soaps are made of either sodium or potassium mixed with oil. Insecticidal soaps are a contact insecticide, meaning they must come in direct contact with the pest to effectively kill them. Insecticidal soaps work on soft-bodied pests such as aphids, caterpillars, thrips, flies, scales and fleas. Hard-bodied insects, such as the beneficial lady beetle, are not affected because the soap cannot penetrate their hard outer body. You can purchase insecticidal soaps from garden supply stores, garden catalogs and online.

Peppers and Herbs

Crushed or ground herbs and peppers also work as repellents for many insect pests. In some instances, simply sprinkling crushed or ground pepper, such as cayenne pepper or chili powder from your pantry, in the soil surrounding your plants or on the plants themselves will repel pests. The pepper's capsaicin, the chemical that produces the hot effect when humans eat them, also works as an insecticide to kill certain pests. Other herbs and common kitchen items to repel pests include garlic, garlic oil, basil and certain other herbs. You can mix the crushed herbs with oils, dish soap, baby shampoo or with water to make a spray for your plants.

Mechanical and Cultural Controls

Mechanical and cultural controls repel and protect plants from insects without the use of any chemicals. Mechanical controls include placing netting around or over your plants; placing sticky or other traps near plants to attract and hold the insects; hand-picking insects off plants; and strong sprays of water. Cultural controls include rotating crops to keep pest populations from building up, destroying crops after their last harvest and getting rid of plants after the last harvest. Mechanical, cultural and biological controls often work, but when they don't, it's time to switch over to organic pesticides.

References

• Michigan State University Extension: Companion Planting
• Washington State University Extension: Insecticidal Soaps
• Purdue University; Organic Vegetable Production; Gerald Brust, et al.
• Auburn University; Highlights of Agricultural Research; Geoff Zehnder, et al.; 1997

Resources

• University of Florida IFAS Extension: Home Remedies for Insect and Disease Control on Plants