The concept of companion planting is not a new one. The first settlers described how Native Americans would plant pole beans along with the corn. The obvious advantage to this is that the robust corn will help hold up the beans, but also – and unknown to science at the time – Rhizobium bacteria colonies on the beans help recapture nitrogen for the legume, so both plants benefit. This symbiosis is at the heart of companion planting.
By now most people have heard the idea of planting marigolds as a border to repel insects, but there are many other choices. This is so because insects use their sense of smell to find the foods they desire, much like we do – in my case grilling steak or pizza fresh out of the oven! So masking the smell of a plant with a much more powerful aroma can chase some bugs away, or just plain hide the desired food smell. For instance, garlic releases deterrent odors that can chase away bean beetles and potato bugs; onions can help protect strawberries and tomatoes; mint may keep cabbage loopers away; and basil is useful against tomato hornworms. But keep in mind that there is no guarantee, these solution only increase your chances of success, but the real dividend here is that you will no longer be using chemical treatments to deter the same bugs.
Aside from repulsion of insects, there are also attractant plants. These are species that destructive insects much prefer to your prized russets or vine tomatoes. Nasturtiums are a veritable vacuum for aphids and flea beetles, Colorado potato beetles love black nightshade, mustard plants draw cabbageworms and harlequin bugs away from your cabbages, and cabbage maggots will leave your broccoli, cauliflower and cabbages be when offered radishes. To make combinations like this effective they must be planted close together. You cannot expect an aphid to travel to the other end of the bed to get to a nasturtium. Also, if the attractant plants get infested with bugs it is a good idea to tear them out complete with the insect population. Make sure to enclose the effected plant with a plastic bag before agitating it from the ground otherwise you’ll be throwing insects everywhere and you won’t contain your problem. Afterwards, replant the area to keep the populations under control.
Not all insects are bad for your garden and nursery crops can help encourage these beneficials. Most of these prefer flowers that are small and abundant such as the daisy family. Asters, coreopsis, dahlias, marigolds and others are all excellent sources of pollen and nectar for beneficials such as green lacewings, parasitic wasps, hoverflies and the good old ladybug. Plant them close to your foodstuff plants so that the bugs are always nearby to police the area. Flowering herbs can also be very good in this respect. Dill, for instance, can attract pest-eating spiders, lacewings and wasps which will help control caterpillars on cabbage, beetles on cucumbers, and aphids on lettuce. Dill also has the added benefit of feeding the pupae of swallowtail butterflies.
True companion plants are those that co-exist in the same area without interfering with each other’s growth and feeding needs. Several things to consider when planting together are the different life cycles, growth habits, rooting patterns, nutrient needs and light and shade tolerance of each plant. For instance, planting the deep-rooted squash with shallow-rooted onions would be a good choice. Heavy feeders like corn and squash can be combined with light feeders such as garlic and beans. Sunflowers and lettuce go well together if the sunflowers offer shade in the hot afternoon sun.
When done correctly a companion planted garden can be beautiful, healthy and productive. In today’s climate of reliance on organic solutions to gardening problems instead of chemical ones, companion planting is an essential step to understanding the ecosystem within your own yard and winning the battle against pests and diseases.