Companion planting – an old-fashioned method of growing different types of vegetable or flowering plants beside each other so that they work together to help each other thrive – is being discovered by modern gardeners and landscapers.
By Wendy Priesnitz
My childhood friend’s grandmother had what some thought was a messy garden. Rather than planting rows and rows devoted to tomatoes, then more rows of carrots, she intermingled various species. She also tucked small plants here and there at the feet of taller ones. And – to the particular disdain of my mother – mixed vegetables and flowers such as garlic and roses in the same garden.
At the time, I thought her garden was beautiful, with all the mixed textures, colors, and sizes of plants. And I now realize that it also must have been highly productive, despite her refusal to use chemicals in her organic garden. The method behind her intermingling madness is called “companion planting.” And that simply means organizing the garden so that plants that benefit each others’ growth are placed in close proximity to each other.
Companion Planting Benefits
The first benefit is more to the gardener than the plants, and that is optimal use of space. My friend’s grandmother must have had a small garden, given the small size of inner city lots. But companion planting allowed her to make good use of all the available room, using the space in the shade of corn plants to grow lettuce, for instance.
The focus of companion planting is that many plants have beneficial properties that can help other plants. By creating a balanced ecological system in your garden, you work with Nature to ensure that all the plants thrive, not competing for light or nutrients, and fending off pests and diseases.
This happens in a variety of ways. Sometimes, a plant is attractive to insects and, when planted beside the main crop, will protect it by luring the insects away. This is called “trap cropping.” A good example of this is when collards are planted to protect cabbages from moths. Likewise, nasturtiums are useful as a vegetable garden trap plant for aphids.
Many herbs are useful in repelling insect pests. And therein lies the reason why my friend’s grandmother grew garlic among her rosebushes and raspberries. Garlic repels aphids, spider mites, fruit tree borers, and even Japanese beetles. Mint is useful against ants and white cabbage moth, rosemary deters carrot flies and bean beetles, and horseradish helps against potato bugs. Both sage and cabbage are attractive landscape plants; planting them together works well because sage can aid in the control of cabbage moths and has also been known to attract beneficial insects such as bees, which are helpful for pollination.
Some plants exude chemicals that actively suppress or repel pests and protect neighboring plants. The African marigold, for example, releases thiopene – a nematode repellent – making it a good companion for a number of garden crops. Marigolds are also a charmingly bright addition to any garden. Less attractive to the eye but just as helpful is rye, which can be used as a mulch around tomatoes and broccoli because it leaches a chemical that prevents weed germination.
Legumes like peas, beans, and cloves have the ability to fix atmospheric nitrogen for their own use and for the benefit of neighboring plants via the Rhizobium bacteria. Hence, the indigenous practice of interplanting beans with corn.
Plants can create beneficial physical habitats for each other. For example, tall-growing, sun-loving plants can share space with lower-growing, shade-tolerant species, resulting in higher yields. This style of planting can have other benefits too. The canopy resulting when corn is companion-planted with squash or pumpkins – another indigenous practice – is believed to prevent damage by the adult squash vine borer. And the prickly squash vines discourage raccoons from eating the corn. The tall, sturdy stems of sunflowers can provide support for a variety of vines.
When dense plants protect vulnerable species by shading or by creating a windbreak, this is called “nurse cropping.” Nurse crops such as oats have long been used to help establish alfalfa by smothering the more competitive weeds.
Companion planting has been used throughout the centuries, with some sources suggesting that it was the early Greeks and Romans who first recognized that certain plants could encourage or inhibit the growth of others. Gardening journals and word-of-mouth through generations of farmers and gardeners kept the knowledge of companion planting alive.
Although my friend’s grandmother’s companion planting methods were probably scoffed at more often than praised, scientists have more recently begun to verify the folklore and further the understanding of why plants enjoy the company of certain other species. When you are planning your companion planting landscape, be sure to consult some of the many resources in the form of books and websites to help you research which plants like (and do not like) others.