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Annual weeds, such as crabgrass, germinate from seeds each spring. After maturing, they drop seeds before dying. These are the seeds that germinate the following year. Perennial weeds, such as dandelions, do not die at the end of growing season. They may lay dormant in the winter, but will become noticeable in the spring. There are also biennial weeds, such as thistle, which grow vegetation in the first year and then flower and die the second year.