Flowering plants attract pollinators and beneficial insects to an edible garden. Photo: Marty Nelson
Many old beliefs about which plants make good companions are based on folklore or trial and error rather than sound science. Fortunately, numerous credible studies and controlled experiments are now helping explain the ecosystems that enable garden plants to thrive. In addition, there are many ways in which one plant can influence another by either enhancing conditions for growth or increased protection against threats.Growing different varieties of plants together increases garden diversity with beneficial results. Photo: Marty Nelson
Flowering plants are important companions to fruit trees and edible plants. They can increase the number and diversity of pollinators leading to higher yields. They can also produce chemical and visual cues that confuse insect pests and make it harder for them to find their preferred host plant on which to feed or lay eggs. Combining members of the aster family (which includes coreopsis, yarrow, zinnias, and marigolds) with cabbage, broccoli, cauliflower, kale, and other members of the cabbage family has been shown to reduce aphid numbers by attracting beneficial, aphid-eating insects. Nasturtiums can help reduce squash bug populations.
Some plants act as traps to lure insect pests away from other plants. Pak choi and radish, for example, are favorites of flea beetles. Planting radish or pak choi a few weeks ahead of new peppers, eggplant, or other transplants can serve to trap the flea beetles and reduce damage to the other vegetables. The combination of basil and tomatoes works as well in the garden as it does in the kitchen. In this example, the basil masks the tomato plants from thrips, small sucking insects that can damage tomato plants and fruit.Sunflowers are friendly to some plants and tough on others.. Photo: Marty Nelson
Plant partnerships work because they support diversity in the garden and contribute to a healthy ecosystem. Not all plant partnerships perform as planned in home gardens. There can be unwanted competition, the timing might be off, or the location might not be right. But even when there seems to be no measurable success, the hidden benefits of an environmentally friendly garden can be appreciated.