What is Companion Planting?
Companion planting is the practice of planting two or more types of plants close together for some kind of benefit, such as the control of pests, increased health and vigour, resistance to disease, or higher yields. These are termed “good companions”.
Companion planting is also concerned with plants are detrimental to each other and must therefore be grown apart. These are termed “bad companions”.
How Does Companion Planting Work?
There are several means by which companion planting works:
Pests Repellent Properties
Some plants exude chemicals from their roots, leaves or flowers that suppress or repel pests and protect neighbouring plants.
Plants of the Legume family, such as peas, beans, clover, lucerne, tagasaste (tree lucerne) and acacias (wattle trees) have root nodules which create a home for Rhizobium bacteria, and these bacteria can take nitrogen from the air and “fix” it into a form that the plant can use. This is a symbiotic relationship, as both the plant and the bacteria are benefited by this teamwork. The nitrogen that is fixed by legumes also benefits neighbouring plants
Pest Decoys (Trap Cropping)
A plant that is more attractive to pests can be planted nearby as a decoy. This creates a diversion to draw pests away from the main plants you are trying to protect.
Many pests identify their food sources through scent or the physical outline (shape) of the plant. Pests can be confused by planting companion plants which release scents which masks that of their neighbouring plants. Companion plants can also be interplanted amongst the crop plant to mask their shape, making them harder to locate, so that pests miss them altogether.
In the permaculture principle of stacking, taller growing plants that need more sun can create supportive cover for lower growing understorey plants that need more shade, and these in turn can create a sheltered ground level for more delicate ground cover plants, which results in all the plants receiving the conditions that they need to grow optimally. The net effect is that more plants are growing in a given space, resulting in higher yields per area.
A nurse crop generally is a crop of trees or shrubs whose height or dense-canopy protects more vulnerable plants during their development from frost, sun or wind.
Habitat for Beneficial Insects
Beneficial insects include pollinators such as bees, predators of pests such as ladybirds, lacewings, hover flies, praying mantids, spiders and predatory mites (OK, the last two are arthropods, not insects!) and parasites of pest such as wasps. Beneficial insects need companion plants which provide nectar as a food source, or a habitat for them to live in. As a simple example, in a corn field, which contains nothing but corn, you have an ideal place for pests that eat corn to live and feed, but nothing to support the “good bugs” that eat these pests, there is nowhere for these beneficial insects to live!
Having a mix and variety of plants together creates a more resilient ecosystem if pests or adverse weather conditions weaken or wipe out a particular variety, or type, of plant. This provides a form of security that ensures that the whole ecosystem does not collapse because one type of plant is attacked or fails.
See the Companion Planting Table listing all the good and bad companion plants here