An annual plant is one that completes its life cycle in one year. It grows from seed, produces seed, and then dies.
Summer annuals germinate in the spring or summer, while winter annuals germinate in the fall.
A perennial plant grows and produces seed year after year. Herbaceous perennials, such as quackgrass and Canada thistle, die back to the ground each year. Woody perennials may drop their leaves, but they do not die back to the ground. The longer that perennial weeds are allowed to grow uncontrolled, the larger their root system becomes, the more they spread, and the harder they are to control. A biennial plant, such as marestail, wild carrot, and dandelion, requires two growing seasons to complete its life cycle.