Q: I’m thinking about planting marigolds around my organic vegetable garden to repel insects. Should I use the tall varieties or the short ones?
A: You should use marigolds in your organic garden – - but not in the manner you describe.
I know that all sorts of organic gardening advisors will tell you to use marigolds to repel insects and nematodes. Unfortunately, when scientists tried the marigold method they found that it didn’t work. French marigolds do help rid a garden of microscopic harmful nematodes but only if the entire garden is planted with them for a full season and the marigold plants pulled and thrown away. The scent of marigold does not repel insects.
Marigolds and other flowers, though, can be wonderful allies in your garden. By planting them among your vegetables, you’ll confuse insects who expect a solid row of the same plant to eat. Insects are not very smart. If you plant beans, then tomatoes, then marigolds, then squash in a row, bugs will be befuddled and not so destructive. If you plant dill, carrots and fennel among your vegetables, they will attract beneficial insects, which will eat most harmful ones.
My experience is that a nice layer of wheat straw mulch between rows is an excellent spider habitat. These eight-legged friends also help you keep insect adversaries at bay. By choosing insect-resistant plant varieties and applying an occasional spritz of insecticidal soap if bad insects get out of hand, you can have a terrific garden without using synthetic pesticides.