Dill, fennel and cilantro have much in common. All three are culinary herbs. They are easy to grow from seed sown directly in the garden in cool spring weather. They are all members of the carrot family. And best of all, when in flower, these herbs are magnets that attract beneficial insects to your garden.
Tiny parasitic wasps drawn to the flowers' nectar will stay around to raise their families, helping control assorted garden pests such as cabbage worms, tomato horn worms, aphids and whiteflies. Delicate-looking lacewings will also come. Their larvae are known as "aphid lions," but besides aphids, they also help control a number of other pests, including thrips, mealybugs and mites.
Tachinid flies are also attracted to the flowers of these herbs. Their larvae help control many other unwelcome garden visitors, including squash bugs and sawfly larvae.
Being a somewhat lazy gardener who enjoys planting and harvesting more than fighting pests, I'm happy to welcome as many beneficial insects as possible. I have packets of dill, fennel and cilantro seeds ready to scatter in flower beds, in mixed container plantings and in vegetable beds. The herbs are skinny enough that they won't crowd their neighbors, and their fine texture combines well with almost any other ornamental or edible plants.
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All that beneficial insects ask besides plenty of flowers for nectar is that the gardener refrains from using pesticides.
You can recognize flowers in the carrot family because their flowers are arranged on short stalks in clusters that resemble an upside-down umbrella. The family is quite large. It includes carrots, of course, as well as parsley and celery. But these plants are slow to flower, and it's the flowers that attract the beneficial insects. Luckily, there are also some beautiful flowering perennials in the family. Golden Alexanders (Zizia aurea), one of my favorites for shady borders, is a Midwest native that grows about 2 feet tall. It not only attracts insect helpers to its flowers, but its foliage also serves as a host plant to the larvae of black swallowtail butterflies. And, in my opinion, a garden can never have too many black swallowtails.
Masterwort (Astrantia major) is another beautiful but underused perennial in the carrot family that thrives in partial shade. Sea holly (Eryngium planum) is a showy relative that grows best in a sunny border.
In addition to the carrot family, the sunflower family also hosts a number of beneficial insects. That family includes not only sunflowers, but also asters and goldenrods.