Perennial are plants that emerge, grow and flower every year. They are also herbaceous, meaning that their stems are not woody like those of shrubs and trees. Perennials are the jewels of the garden. Many perennials are evergreen, but most are not: their foliage dies back in the autumn while their roots survive underground so that the plant will emerge again every spring. By making a careful choice of varieties, the flowering periods of perennials will succeed one another from as early as January until as late as December.