In nature, it is rarely usual to see just one type of plant in an ecosystem, so why do we sometimes plant mono-cultures in our vegetable plots and garden beds? Planting areas filled with just one sort of plant increases pest problems and can lead to reduced disease resistance and increased incidence of diseased specimens. Companion planting is the careful choice of plants to combine in your garden. Companion plants are plants that are said to have some sort of beneficial interaction with one another. Science has not as yet fully explained all the mechanisms for plant interaction and it is thought that this may be far more complex than previously imagined. Experimenting with companion planting, whether it truly is efficacious or not, will almost certainly enrich your garden in one way or another, if only through increased biodiversity.
Companion plants are said to benefit one another in a variety of different ways. Here is a brief and incomplete guide to the ways in which some plants can benefit others, along with some examples of the types of plant companion that operate in this way:
Nitrogen Fixers and Dynamic Accumulators:
While there has been little rigorous scientific research done into the various plant interactions, there is a wealth of anecdotal and empirical evidence that suggests that certain plants are better than others at collecting nutrients and making those nutrients available to other plants. Some plants, legumes for example, have a symbiotic relationship with beneficial bacteria on their roots which allows them to take nitrogen from the air and make it available in the soil in a form usable by other plants. Other plants like dandelions and comfrey have deep tap roots which allow them to withdraw nutrients from deeper in the soil, meaning those nutrients can then be made available to other plants.
Pest Prevention and Distraction:
Some plants benefit those around them by repelling certain pests. Marigolds are said to be a universally excellent companion plant as they provide an effective nematode control. Nasturtiums and alliums have a deterrent effect on aphids and can distract a whole range of pests who are put off by the smell. Companion planting lists will tell you a whole range of interactions which are little studied but widely accepted. For example, planting carrots with onions will mingle the two smells and onion and carrot flies will not be able to discover your crops.
Beneficial Attraction:
Some plants are excellent companions because they attract predatory insects, for example ladybirds that will eat aphids. Others are excellent at attracting bees and other pollinating insects, thus increasing chances of pollination occurring on neighbouring plants. Some plants earn their place in your garden simply by being good at attracting beneficial insects and wildlife.
Generations of gardeners have experimented with companion planting and have discovered combinations that work for them. Other anecdotal interactions that have been recorded include the idea that basil improves the flavour of tomatoes, though this is thought unlikely, it seems planting basil with tomatoes can increase yield quite considerably.
There is much more to learn about companion planting, so give it a go and see what happens in your garden.