Studies show that it can help against thrips that stunt tomato plant growth and cause early fruit drop, and may limit egg laying by adult moths whose larvae are the all-too-familiar (and voracious) tobacco and tomato hornworms. It also works against yellow-striped armyworm moths.
Pair your potatoes with catmint (Nepeta) to deter Colorado potato beetles; partner calendula with collards to keep aphids at bay. To limit cabbage worms, plant brassicas with sage, hyssop or chamomile. (The bonus with chamomile: plenty to harvest and dry for tea.)
Other useful herbs include many umbellifers, members of the carrot family (Apiaceae). Flowers of dill, fennel, cilantro, parsley and chervil may attract predators of various species of aphids and caterpillars, luring helpers like parasitic wasps, tachinid flies, ladybugs and lacewings.
Umbellifers can help with aphid control among lettuce and leafy greens; with cabbages, try leaving the cilantro to flower. Dill’s ferny foliage has also been shown to protect broccoli from imported cabbage worms, reducing their egg-laying behavior. And if you have Colorado potato beetle problems with your eggplants, dill and cilantro may help there, too.
More Flower Power
Besides the nasturtiums and the flowering herbs, there are two familiar annual flowers that Ms. Walliser has come to rely on after consulting the research: sweet alyssum (Lobularia maritima) and cosmos.
In organic lettuce farms in California, she said, strips of sweet alyssum are alternated with lettuce to enhance biological aphid control.
Cosmos help against aphids, too, particularly around brassicas like broccoli and cauliflower. And so do other aster family members, including sunflowers, Rudbeckia, Coreopsis and zinnias, by attracting beneficial predatory insects.
