Vegetable growers and farmers who want to avoid using pesticides on their crops sometimes use companion planting, but you can practise the same techniques in the rest of the garden.
How does it work?
The theory works on many different levels. It is about choosing plants that have additional properties and functions, beyond simply being ornamental or a food supply, and using them in combination with one another.

Plants can benefit their neighbours in different ways by:

• giving off scent or chemicals that repels insects;
  attracting beneficial insects that are predators to harmful insects ;
  attracting insects that are pollinators for other plants;
  attracting harmful insects and therefore distracting them from the main prize crop;
  absorbing minerals from the soil so they can be ploughed back into the soil as fertiliser, for example, green manures;