How long does it generally take for a biennial weed to complete its four stages of development?

Biennial weeds are unique in their life cycle as they take two years to complete their development. In the first year, they typically germinate and grow vegetatively, forming a rosette of leaves close to the ground. During the second year, they transition into the reproductive phase where they flower, produce seeds, and then die. This two-year cycle characterizes biennial plants, setting them apart from annuals, which complete their life cycle in one year, and perennials, which live for multiple years.

Thus, the answer indicating that it takes over a two-year period accurately reflects the biological and developmental traits of biennial weeds.