by Ron Kushner, for the Shuttle

There are many herbs that work as companion plants, but I am focusing on three — coriander (cilantro), borage and tansy — for to their ability to repel many insect pests.

Coriander/Cilantro (Coriandrum sativum)

Coriander is a fast-growing annual that grows 1-3 feet tall and matures quickly in cool weather. (It tends to bolt once the weather warms.) The upper leaves look like dill and the lower leaves resemble Italian parsley. Both the leaves and the seeds are used as seasoning in a variety of cuisines. It is a member of the carrot family, with umbels of white or very pale lavender flowers. Native to Eurasia, the plants can take full sun for at least a half day, if not more, but coriander actually tolerates more shade than most herbs. The plant repels aphids, Colorado potato beetles and spider mites — and bees love it!

It is a good companion to asparagus, potatoes, Brussels sprouts, carrots and peppers, but do not plant next to fennel. Direct-sow seeds in the garden. The seeds are large and the plants grow very quickly. They develop a long taproot, so they do not like to be transplanted. The soil should be well drained and moist. Fertilize with 5-10-5. 

Coriander leaves can be harvested until the plant goes to seed. If you want to harvest the seeds, wait until they turn brown, cut off the branches and hang upside down in a paper bag to catch the seeds as they fall off. Remove any of the hulls and make sure the seeds are dried well before storing.

Borage (Borago officinalis)

Borage is an annual and needs to be replanted each year, although the seeds will self-sow. It can grow into a fairly large bushy plant 2 or 3 feet tall and just as wide, with star-shaped, electric-blue flowers with hairy stems and leaves. It prefers cooler weather, average soil on the dry side and at least a half day of full sun. The plants will falter in hot, humid summers.

Direct-sowing in the garden is recommended. The seeds are large and grow quickly but should be pre-chilled in the refrigerator a week or so. Cover the seeds, as they need darkness to germinate.

Borage is a good companion to beans and corn and it is said to improve the flavor of tomatoes and cucumbers. It will repel many common pests such as cabbage worms and tomato hornworms. It is a great favorite of bees of all types. There are only three species, all native to the Mediterranean region.

Both the leaves and the flowers are edible and the new, young leaves add a cucumber flavor to salads. They can be fertilized with 5-10-5.

Tansy (Tanacetum vulgare)

Tansy is a hardy perennial herb with attractive flowers closely related to chrysanthemum. It has been grown since ancient times to repel a variety of bugs. But the plants can spread invasively through underground runners so it may be better to keep in containers throughout the garden area.

It grows to 3-4 feet tall and tolerates poor, dry soil, but needs to drain well. Better to be kept loamy and moist. The foliage is strong scented and used as an insect repellent. It has a “peppery-camphorous” aroma. 

It blooms all summer with flat clusters of lots of half-inch wide yellow flower heads that look like gold buttons.

It is a great companion for beans and attracts beneficial insects to control cabbage pests. It also help to deter and repel many flying insects. It repels green peach aphids and squash bugs from susceptible garden crops, along with many beetles, flies, cutworms and ants. You can also brew a tea from tansy leaves and spray it on other plants to repel insects.