Perennial and biennial herbs should be winter protected. Many herbs are shallow-rooted, which makes them susceptible to heaving during spring thaws. Mulch with straw, oak leaves, or evergreen boughs 4 inches deep to protect the plants. Appy the mulch after the ground has frozen in early winter. Do not remove the mulch until plants show signs of growth in early spring. Early removal could result in some early frost damage.