Stefan says: I know the feeling! Above all, a weed species must be a good competitor, and it’s a feature of many of the most successful weeds that they have evolved the capability of growing in a wide range of habitats, including our gardens. Many weeds produce large quantities of seeds per plant that may be able to germinate without having to pass through a period of winter dormancy. Some weeds, such as chickweed and groundsel, can even germinate and grow so quickly as to pass through several generations in a single season, even though the output of seeds per plant is relatively low. Allied to the production of large quantities of viable seed is the possession of an efficient means of dispersing them: by explosive discharge, by wind or water, by gardeners or by animals – either externally, by adhering to their coats, or internally, as often happens with birds, by surviving the digestive tract.
Even so, not all weeds depend on seed production, and the most serious difficulties arise with deep-rooted perennials, such as bindweed; with those like celandine that produce masses of small survival structures, called bulbils; and, of course, with those like horsetail that are barely affected by weedkillers. By its very nature, an invasive underground root or rhizome is highly undesirable in a cultivated plant, so any weed species having this method of growth will have an advantage in its competition for the soil.
But there’s one rather
