Companion planting is a system of planting a number of different plants together, so that they benefit by from their close association. Sometimes in agriculture we may see monoculture, an areas where there is a single crop or plant species. Whether its a plantation, a field or a garden bed or even a row this makes it easier for disease to spread and pests to invade.
In nature its much more common to see a diversity of plants intermingled and growing together. The plants thrive more from their association with other plants in a number of possible ways. Companion planting grows a variety of plants together for some mutual benefit.
Unfortunately there is a lot of myth and misunderstanding about companion planting. Companion planting is often portrayed like a Hollywood romance, an instant attraction followed by happily ever after. A helpful rule to remember is that companion planting will help solve a problem ONLY if that problem exists. The problems that need solving are dependent upon the local conditions, and so the effectiveness of companion planting will vary as much as the relevant local conditions vary. The problems of Europe may be no-existent in the US., the pests of North America may be absent from Australia. The soil conditions of one neighbourhood may be completely different to those of the next village. The conditions of shade, competition and previous use may be completely different in one back yard to that next door.
Occasionally plants that benefit each other in one situation may have the opposite effect in another.
Companion Planting and Nutrition
One way that some plants can support others is by providing some nutritional element that is needed. Most commonly nitrogen fixing plants provide support for root crops and heavy feeders. Deep rooted plants can absorb a variety of nutrients from deep down in the soil, and make them available to other plants when leaves die back or are added to compost.
Companion Planting and Pests
If a disease or pest is present in the local environment, whether that is country, region or garden bed companion planting may help. Pests find their target plants in a number of ways the action of the companion plants needs is related to this process.
Pests and diseases in the soil will be affected by plants that releasing a chemical into the soil that kills or repel that pest. Feeding insects may identify their host plants by scent, in which case a plant that produces a masking odour would be a good solution. Other insects identify their food by sight, so disguising their shape with plants of a totally different silhouette will confuse the miniature munchers.
Attracting predators that eat your garden pests is another way that companion planting can benefit your veggie patch. Alternatively luring pest away from your vegetables to an alternative planted as a “trap crop” can be a solution. I have heard of weeds being used in orchards and vineyards for this purpose.
Companion Planting for other reasons
Other reasons for companion plating are to attract pollinators, create a micro-climate, or even just the convenience of having plants with similar water and nutritional requirements together. Sometimes plating some crops together can even improve the flavour of crops on your plate.
Allopathy or Competition Between Plants
Some plants actually inhibit the growth of other plants by competing for the same resources, or by creating an incompatible environment such as a growth inhibitor or making the soil too rich for a particular plant. Inhibiting the invasion of your vegetable plot by weeds and grass is advantageous, but inhibiting the growth of one vegetable by another is something you will want to avoid.
Companion Planting in Practice
Overall multiple plants grown together in the same garden bed can improve yields and crop quality. Best results are obtained by developing your understanding of companion planting in your plot as your gardening experience grows. Experimentation and record keeping will build knowledge, and that is one of the roles of this website.