When a plant is called ‘herbaceous’, it means the core stems that hold the leaves upright during the growing season are soft, green or succulent, as opposed to the brown and woody stems of a lilac, forsythia or rose of sharon.
Most plants that are defined as ‘herbacious’ will die back to the ground in winter and the spent stems and foliage are pruned back to the the gardens soil. The roots of these perennial plants are alive and well, and new growth will emerge from the ground in spring.
Good examples of herbacious perennials would be peony, coreopsis, cone flower, blanket flower, Mexican primrose and many more.
‘Woody Perennials’ do not die back below the soils surface. Typically, these woody shrubs drop their leaves for winter after thier spectacular show of autumn foliage colors. The same stems that held their foliage last year, will reemerge with fresh new leaves in spring. There is no need to trim last years plant all the way back to the gardens soil.
Good examples of woody perennials would be lilac, spirea, salvia, potenilla, hardy hibiscus, crape myrtle and many more.