By Christy Wilhelmi, Organic Gardening Instructor
Although many will disregard companion planting and see it as old wives’ tales, many plants, flowers and herbs do defend themselves against insects by being poisonous to them or developing a strong scent that frightens them away, and it is possible that a plant growing close by might benefit from being in this bug-free zone.
Although companion planting is also mixed up in folklore, there is also an element of fact, and this method can be happily adopted by those who practice organic gardening.
For example, French marigolds (Tagetes patula) secrete an enzyme or a hormone into the soil that deters nematodes from infesting their roots, and it does seem that tomatoes or other nematode susceptible plants growing as neighbors will be protected.
It may be significant that most of these beneficent plants are strongly aromatic. Planting dill with your tomatoes will attract the tomato worm for you. Planting nasturtiums will take care of cabbage white butterfly caterpillars and great for repelling white fly. They are also good for planting under apple trees to get rid of colding moth. Nasturtiums are planted among cucumbers for protection against the cucumber beetle and the Mexican bean beetle. Nasturtiums and tansy help get rid of the Colorado potato beetle, and catnip and nasturtiums for repelling the green peach aphids.
If you want to get rid of aphids then you will need to interplant with sow thistle, stinging nettles or broad beans. Sunflowers will help trap harlequin bugs, and potatoes, calendula daisies are good for earwigs.
On the flip side, there are steps you can take to attract good insects. If you think the common dandelion is a scourge in the garden, think again. It is now known that dandelions attract pollinating insects. Furthermore, they also release ethylene which is a gas that encourages fruit setting and fruit ripening.
Daisies, dill, coriander and parsley are all good for attracting beneficial insects into the garden. The pollen they provide make them wonderful bee plants, but in addition they also attract parasitic wasps that prey on insect pests.
These plants should be planted throughout the garden at regular intervals because many of these wasps are tiny and fly only over short distances. Larger predatorial insects like lacewings and hoverflies also feed on the pollen. By allowing these plants to go to seed, not only are you keeping the insect population in check, but you can save seeds at the same time for next planting season. Herbs too have been known to repel certain insects. Southernwood is good for repelling the cabbage butterfly and tobacco for flea beetles.