Foeniculum vulgare variety dulce is the botanical name for this half-hardy or biennial, Sweet Fennel. This herb resembles Dill, but its finely divided, anise-scented foliage is light green instead of blue green and its stems are solid, not hollow like Dill's. Sweet Fennel can grow 4 to 6 feet high in flower. The yellow clusters of flowers aren't abundant until the second season, when the plants are sturdy enough to support good seed yields.