The Hyssop genus (Hyssopus) belongs to the mint family (Lamiaceae) and contains several species of herbaceous perennials. These plants typically thrive in warmer climates and generally prefer sunny locations. Home gardeners should select Hyssop plants according to plant hardiness, bloom time, intended use and general culture. Many Hyssop plant varieties perform well in American gardens.
Yellow Giant Hyssop
The yellow giant hyssop (Agastache nepetoides) blooms spikes of small, yellow-green flowers from July through September. This fast-growing variety features arrowhead-shaped leaves and long, stiff stems that reach up to 6 feet in height. Yellow giant hyssops tolerate the hot, humid summers of the American South. This low-maintenance plant prefers rich, moist soils. Gardeners often plant yellow giant hyssop plants in butterfly gardens, perennial borders and woodland gardens.
The anise hyssop plant (Agastache foeniculum) naturally occurs in the American Midwest and Great Plains regions. This hyssop species forms clumps ranging from 2 to 4 feet in height with slightly smaller spreads. Lavender to deep purple flower spikes bloom from June through September. This plant also bears square stems and fragrant, dull green leaves. Anise hyssop plants perform best in fully sunny locations with good drainage. Powdery mildew and rust sometimes occur in poor-draining soils. The anise hyssop works well in butterfly gardens, wildflower meadows and herb gardens.
Blue Giant Hyssop
The blue giant hyssop (Agastache foeniculum), sometimes called the lavender hyssop or the fragrant giant hyssop, bears oval, aromatic leaves with green tops and light undersides. This ornamental plant ranges from 2 to 4 feet in height. Purple to blue flowers bloom in July and August. This plant prefers well-drained, sandy soils. Gardeners often use the blue giant hyssop in butterfly and hummingbird gardens.
Purple Giant Hyssop
The purple giant hyssop (Agastache scrophulariifolia) naturally occurs around thickets and woods in the Eastern United States (U.S.). This hyssop species blooms from July through September, displaying spikes of red to purple flowers with deep purple flower bracts. Stiff, purple-green stems reach up to 5 feet in height. The oval, green leaves have pale undersides. The purple giant hyssop makes a nice addition to a butterfly garden.
The water hyssop (Bacopa monnieri), sometimes known as the herb-of-grace, is a semi-aquatic plant that belongs to the snapdragon family (Scrophulariaceae). This hyssop variety features glossy, green leaves and bell-shaped, white flowers that bloom from April through September. These white blossoms sometimes have blue or pink tints. Water hyssop reaches less than 12 inches in height and often forms dense mats when planted in damp soils. Gardeners often use the water hyssop in ponds, stream margins, bogs and water gardens.
Hyssopus officinalis naturally occurs in Europe, but typically performs well in warmer American landscapes. This shrubby hyssop species reaches between 18 and 24 inches in height with slightly smaller spreads. Spikes of tubular, blue-purple flowers with showy stamens bloom from June through September. This variety also bears thin, aromatic leaves. Hyssop plants tolerate some drought conditions once established. Hyssopus officinalis plants work well in containers, herb gardens or rock gardens.