Culture
Best grown in loose, medium moisture, well-drained soils in full sun. Plant in sheltered locations north of USDA Zone 7. In USDA Zones 5 and 6, this shrub often suffers winter dieback or dies to the ground. It is not considered reliably winter hardy throughout USDA Zone 5. Even though plants may die to the ground in Zone 5-6 winters, the roots often survive the winter and push up as much a 4-7' of new growth the following year. Because flowering appears on new growth, winter dieback or pruning back to the ground will not affect flowering. In the St. Louis area, this shrub is often regularly pruned close to the ground in early spring each year in somewhat the same manner as is also usually done with crape myrtles.
Noteworthy Characteristics
Vitex agnus-castus, commonly called chaste tree, is typically grown in warm winter climates as a vase-shaped, deciduous shrub (to 10-15' tall) or trained as a single trunk tree to 20' tall. In cold winter areas in USDA Zones 5-6, it is more often grown as a 3-5' tall herbaceous perennial. Features aromatic, compound, palmate, grayish-green leaves with 5-7 lance-shaped leaflets (each leaflet to 6" long) and tiny, fragrant, lavender to pale violet flowers appearing in loose panicles (to 12" long) in mid to late summer. Flowers are quite attractive to butterflies.
Genus name comes from the Latin name for V. agnus-castus or chaste tree.
Problems
No serious insect or disease problems. Leaf spot and root rot are occasional problems. Winter hardiness in the St. Louis area is a concern.
Uses
Interesting foliage and late summer flowers. Shrub borders, foundations, cottage gardens or butterfly gardens.