Vitex, a large deciduous shrub, grows 15 feet tall and 15 feet wide. It thrives in USDA Plant Hardiness Zones 7 to 11, and prefers well-drained soil. Vitex, also known as Chastetree, does not grow well in a wet or boggy location. Although the leaves produce no fall color, they have an attractive blue-green look during the summer. Vitex produces tall spikes of purple or lavender flowers during the growing season on new wood. To encourage more blooms, the shrub is often pruned several times a year after each bloom period before seeds begin to form. If the blooms are allowed to go to seed, the plants will spend energy making seed rather than new blooms.
Prune your Vitex in late winter or very early spring when the weather is beginning to warm. If you prune the Vitex in the dead of winter, the Vitex may lose moisture from the pruning wounds and freeze to death if there is a hard freeze.
Decide how you would like the Vitex to grow. If the Vitex has a strong central leader growing from the middle, it can be shaped into a small tree. If it has several branches coming from a low point near the ground, it can be trained as a large shrub.
Locate the longest branches first that need to be removed and cut them back to a main stem or trunk. This helps the Vitex retain a natural shape rather than trying to shear it all back to the same level. Keep locating the longest branches and cut them back to a main stem until the correct height and width is desired. The branches you remove will get smaller as you work.
Trim off all old blooms and seed heads by cutting at least 2 to 3 inches below each seed head. Cut back to a point 1/4 inch above a leaf node. A leaf node is the swollen area located on the stem from where the leaves grow. Cut all the old blooms back to a level where the plant is evenly pruned and has an attractive shape.
Wait until all summer blooms have faded before deadheading, or trimming the old blooms off, to encourage another bloom period on the new wood. The following winter or spring, prune the Vitex as needed to retain shape and repeat the deadheading process in the summer to produce more blooms.