Companion planting – what is it?
Companion planting refers to a style of inter-planting that results in a beneficial outcome to the gardener usually in the form of higher crop yields and to the plants. Inter-planting is planting different types of plants together.
So instead of having a monoculture – one type of plant, we have a polyculture – many types of plants. There are a number of different reasons for companion planting. The reasons relate to the actions one plant has upon another.
Nutrition based companion planting
Companion planting for nutrition is where one plant provides one or more nutrients in excess. That excess might be utilised by another plant.
For example we might grow peas and beans with our broccoli and kale. The reason for that companionship is based on nutrition sharing.
Peas and beans and other legumes are ‘nitrogen fixing‘ plants. They can make plenty of nitrogen and broccoli and kale and other brassicas want heaps of nitrogen.
Therefore, the broccoli and kale (or other nitrogen loving plants) would benefit from the excess nitrogen produced by the peas and beans (or other legumes).
Using plants as a scent shield
We might use Rosemary or Lavender with some crops to create a scent shield. This is based on the fact that some insects use scent to locate their favourite plants.
The scent from the Rosemary or Lavender (or another scented plant) hides the scent of our other susceptible and valued plants. That serves to cloak susceptible crops using an overpowering scent.
We could have an effective scent shield from fragrant flowers. That would serve the dual function of providing a scent as well as nectar and pollen for predatory and beneficial insects.
Companion planting to disguise a plants shape
We might companion plant to disguise a plant’s shape.
We’d do this because we know that some insects recognise their beloved plants by their silhouette or their shape – from above.
The idea here is to camouflage and alter the shape of the susceptible plant.
So we might grow taller or vining plants to serve this purpose. Our peas and beans might work with out brassicas for this reason. We’d allow the peas and beans to grow up and through our brassicas thereby disguising their shape from above.
Companion planting for root exudates
Most if not all plants excrete root exudates. These secretions attract and/or repel particular microbes.
For example, some marigolds excrete root exudates that poison some root feeding nematodes. However some marigolds attract and feed some root feeding nematodes.
For more information on plant exudates etc, read my blog on Susceptible and resistant plants: what are they and how do they work?
Companion planting to increase predators
Most of our herbivore insect problems can be addressed by nature. If we attract our predators we often don’t need to worry too much about some aphids, mealy bugs and others.
We can attract insect predators such as lace wings, lady beetles, wasps and hover flies by providing them with flowers rich in nectar. We also provide them with the herbivore insects they like to eat.
So when we have insects such as aphids or mealy bugs or scale, we look for our predators.
Hornets and some wasps are excellent at gathering the caterpillars from our gardens. Birds are also excellent at this.
Birds can also take care of grasshoppers and katydids. We attract them by creating gardens that provide them with pesticide free food rich in insects and nectar and hiding places.