Weeds are simply plants that grow where we do not want them. They are often fast-growing and invasive and able to survive in almost any soil or site. Their greatest drawback however, is that they compete with cultivated plants for space, light, water and food. Ornamental cultivated plants, such as poppies (Papaver) or mind-your-own-business (Soleirolia soleirolii), can also be classed as weeds if they become too invasive for their site or if they self-seed freely throughout the garden.

In this section we look at the two different classes of weeds (annual and perennial), along with information on how to prevent and control their spread.