Crown Vetch
This invasive species is difficult to control, as it has a broad environmental growth tolerance and rhizomes (horizontal, underground stems) that can grow up to 10 feet per year. One plant, alone, can completely cover 70-100 square feet in 4 years, growing low to the ground, climbing over and smothering native shrubs, saplings, and other herbaceous vegetation. The seeds from one of these plants can remain viable in soil for up to 15 years. Crown vetch changes the composition of soil in native ecosystems through intense nitrogen fixation. It is very green from early spring through late fall, with purple and pink flowers blooming in summer.