I sometimes wonder where old wives’ tales start. I picture an old wife named Flo, rocking on the porch with her old husband Eb, dispensing advice to gardeners. I am sure it was Flo who came up with the idea that Irish Spring soap deters deer. (It may, but only briefly). Or that Skin So Soft lotion repels mosquitoes. (Not for me.)
There is truth in a lot of gardening folklore, and any old maxim is worth checking for that grain of truth. But the natural world is magnificently complex and tends to laugh at our handy little magic bullets.
Take companion planting, for example. You’ll see lists of plants which, if grown side by side, are said to help one another. And, in fact, the natural world is full of organisms that have coevolved to their mutual benefit. But when plants typically keep company with one another, the association can take many forms. They may simply prefer the same conditions — a moist, acid woodland, for example — or a microscopic soil organism may unite them, as is the case with truffles and oaks. Sometimes one plant will prepare a spot for another, as legumes do for food crops that require plenty of nitrogen. Other times it’s just a matter of dividing up underground real estate, as when deep rooted Queen Anne’s lace occupies one stratum in a meadow, while shallow-rooted, wild onion colonizes the surface (the lesson here: you might interplant leeks and carrots). Studying relationships such as these can make you a better gardener.
It’s the claims made for plants that repel pests that always make me skeptical. You hear that planting strongly aromatic herbs will drive out mischief makers, but I suspect the protection only extends to the pungent plants themselves, not their neighbors.
We’re told that marigolds planted in the vegetable garden deter pests, especially the root-knot nematode, a microscopic worm that can be a serious problem in areas with warm, sandy soils.
Does this work? Yes and no. Researchers find that marigold roots can emit enough ozone to trap and kill nematodes, but it has to be the right marigold (Taygetes patula, or French marigold) and only certain species of nematode are affected. Some nematodes are actually attracted by marigolds, as are whiteflies and spider mites.
Also, marigolds don’t repel nematodes just by growing there and blooming. You must plant them thickly throughout the whole affected area, then till them under in fall to lend protection to next year’s crops. And marigolds may even be allelopathic, that is, toxic to some vegetables, such as beans and cabbage. This is companion planting’s flip side.
So it’s not as simple as just planting a row of the ‘Nema-gone’ marigolds that one popular seed catalog cheerfully promotes.
What you can do is sustain the creatures that help keep pest species in balance; these helpers include birds, spiders, snakes, frogs, bats and a host of predatory insects as well. Your garden is not the set of an action movie in which there are “good guys” and “bad guys,” but rather a complex web of interdependent species that are used to working things out without your help.
The most important step is to not use toxic substances against any of them.
The next step is to try to create a diverse habitat in which as many species as possible can thrive. You’ll need moist, mulched, shaded areas for the beetles, berries for the birds, sunny places for butterflies and compost-rich soil for all the essential bacteria and fungi that make things grow.
It also helps to grow lots of the plants that insects love. Members of the carrot family (Apiaceae, formerly Umbelliferae), which includes dill, fennel, coriander, angelica and yarrow, attract not only important pollinating insects, but also predators like lady beetles, ichneumen wasps, lacewings, hoverflies and pirate bugs that feed on inconvenient species such as aphids, mites and scale. The flowers of these plants are umbels — little flat-topped flower fields offering up tiny nectar-filled cups from which even small insects can feed.
The daisy-shaped members of the Asteraceae family, such as shasta daisies and black-eyed Susans also are good insect plants. Include them in meadow plantings and flower gardens. So are the Brassicaceae such as cabbage, mustard and broccoli. Leave them in the vegetable garden even after they’ve gone to seed. Have plenty of flowers blooming all the time. Cultivate curiosity about insects, rather than hostility and fear. Give your plants the fertility and moisture they need to grow vigorously and better resist predation.
And if you happen to find a brand of soap that can get the imbedded grime out of an old gardener’s hands, send me a bar and I’ll help you to start a rumor. Flo would be proud.
Barbara Dasmrosch’s latest book is “The Four Season Farm Gardener Cookbook.”