Insects are everywhere, with more a million different species on earth. Some are helpful and beautiful, like bees and butterflies. Others cause trouble, like mosquitoes and ticks that suck your blood and spread illnesses. Some leave you alone but eat your fruits and flowers.

When I saw that Coastal Maine Botanical Gardens in Boothbay was offering a member-only tour about plants that repel unwanted insects, I jumped at the chance to join the tour. I was “wait listed” – clearly I’m not the only one who’d like some help warding off garden bugs without resorting to pesticides – but received notice the day before the tour that I could participate.

Jen Dunlap, a staff horticulturist, led about 15 of us through several core gardens (the ones closest to the visitor center), talking about different plants as we saw them, describing what pests they repel and providing hints on how to grow them.

Some of the best insect-repelling plants turn out to be herbs we grow to flavor our food.

“All of the fragrant herbs have volatile oils that are released in cooking,” Dunlap said, “and those same oils are released by the heat of the summer.”

Those herbs – including basil, rosemary, thyme, sage, dill and fennel – repel flies, mosquitoes, moths, earwigs and a host of other insects.

More than half of the 90-minute garden walk was conducted in the Lerner Garden of the Five Senses – covering touch, smell, sound, sight and taste. The garden shows how to mix ornamental plants with herbs and vegetables.

First, most of the herbs and many of the vegetable plants are attractive in their own right. And, since the fragrant herbs repel so many pests, having them in the garden improves food production.

Alliums, the onion family that includes leeks and chives, are grown as both ornamentals and food crops, and all of them repel pests, Dunlap said. So rather than limiting your onions in one area of your vegetable garden, you can intersperse them throughout your gardens, covering a larger area. You might grow them in your flower gardens, as well.

Sometimes plants get rid of pests not by repelling the troublemakers but by attracting insects that kill insects you don’t want. For instance, the herbs dill and fennel, along with the ornamental annuals alyssum and calendula, are hosts to the tachinid fly. I’ve written about the tachinid fly before as the insect whose eggs show up as white spots on the backs of Japanese beetles and eventually kill them. It turns out tachinid flies also kill sawflies, cabbage worms, earwigs, gypsy moths, cutworms, tent caterpillars, squash bugs and others. (Earwigs, incidentally, though they eat plants, among them hollyhocks, zinnias, dahlias and shasta daisies, do have benefits, Dunlap said. They break down soil in compost bins and prey on aphids and flies.)

Calendula, dill and alyssum are annuals, but they self seed, so you probably will have to plant them only once, while fennel is perennial.

Mints repel ticks, Dunlap said, and ticks are responsible for the recent epidemic of Lyme disease. In theory, mint should be planted in everyone’s garden, but mint is a thug, spreading wildly, strangling nearby plants and almost impossible to eradicate. One that is less aggressive, Dunlap said, is hairy mountain mint or Pycnanthemum verticillatum. During the tour, the mint’s dainty white flowers were covered with bees – a bonus.

A shrub that repels ticks is beautyberry, or callicarpa, which has pink flowers in summer and purple berries in the fall. It does have a lot of winter dieback, but usually recovers.

Lavender is one of the best moth and insect repellent going. “That is why people put lavender sachets in drawers of clothing and have used it in laundry,” Dunlap said.

It is a beautiful, fragrant ornamental and easy to grow. Catmint has many of the same qualities, but is not quite as strong-smelling nor as effective. If you have cats, however, they will love it.

In addition to hosting the tachinid fly, calendula repels flies, moths, aphids and mosquitoes, Dunlap said, mostly by aroma. It is an attractive plant with long-lasting, daisy-shaped flowers.

Marigolds are the first plant many gardeners think of as insect-repelling plants, and for good reason. They work well, Dunlap said, especially on caterpillars.

And chrysanthemums, usually planted for their fall display of color, also repel a wide variety of insects. The once-popular organic pesticide pyrethrum is derived from chrysanthemums, specifically pyrethrins, which are the active source of the plant’s insect-repelling power. Pyrethrum is less popular than it once was because it turns out it kills beneficial insects as well as pests.

For most of Maine this next plant won’t help, but for those few who are in Zone 6 – right along the coast from about Owls Head to Bath and in the southern tip of York County – try planting four o’clocks, aka Mirabilis jalapa. The attractive flowers bloom late in the day – when the light begins to decline – and, unusually, several different-colored flowers bloom on the same plant. The botanical garden sits in the heart of Zone 6, and excepting occasional dieback, the four o’clocks survive fairly well there. Why would you want to bother with such a finicky plant? Because it lures Japanese beetles and then poisons them. That is my kind of plant.

Dunlap says in cooler zones you might have a microclimate, such as the western side of the house or where the drier vents, that would enable you to plant four o’clocks. I wonder if I could move the drier vent to the west side of our house.

Tom Atwell is a freelance writer living and gardening in Cape Elizabeth. He can be contacted at 767-2297 or at: [email protected]