Chaste tree (Vitex agnus-castus) is a deciduous shrub that bears clusters of purple flowers in the summer. Left unpruned, it can become a sprawling, vase-shaped shrub that grows to 20 feet tall with an equally wide spread. It is sometimes trained as a single-trunk small tree.
The leaves of the chaste tree are very reminiscent of the marijuana plant (Cannabis sativa), with five leaflets in a palm-shaped arrangement. The leaves have a fragrance similar to that of the herb sage. The purple flower clusters (called panicles) look like those of the butterfly bush (Buddleja spp.) Varieties with white flowers are also available. The black fruit contains four seeds that look like peppercorns and are sometimes used to flavor food.
Historically, the fruit of the chaste tree was used in ancient times to treat reproductive problems. The name "chaste tree" came about because consuming the flowers was thought to suppress libido.
This is one of the only species within the Vitex genus that is native to temperate regions; nearly all others are tropical trees and shrubs. In colder climates (zones 5 and 6), this plant sometimes dies back in winter and is grown as a perennial, in much the same way that the butterfly bush is grown in climates with freezing winters.
Like most shrubs, chaste tree is best planted in the spring to give it plenty of time to establish roots before winter dormancy. It is a fast-growing shrub that can shoot up as much as 7 feet in a single season. Most gardeners keep this plant to 10 feet or less in height.
|Botanical Name||Vitex agnus-castus|
|Common Names||Chaste tree, lilac chaste tree, chasteberry, vitex|
|Plant Type||Deciduous shrub|
|Mature Size||8 to 10 feet tall; 5- to 8-foot spread|
|Sun Exposure||Full sun|
|Soil Type||Loose, well-drained soil|
|Soil pH||5.6 to 7.5 (acidic to slightly alkaline)|
|Flower Color||Violet, blue|
|Hardiness Zones||6 to 9 (USDA)|
|Native Area||Mediterranean, Asia|
How to Grow Chaste Tree
Chaste tree is an easy-to-grow shrub that poses few challenges to a home gardener. If you avoid soil that is too wet or dense, success is nearly guaranteed. The biggest downside to the chaste tree is that it may grow too aggressively, requiring frequent pruning to keep it in check. It can, in fact, escape a garden and become invasive if it naturalizes in the wild. This is a problem mostly in certain areas of southern U.S. states—call your local garden center or cooperative extension service to seek advice on growing chaste tree.
Chaste tree will grow well in full sun to part shade, though best flowering occurs in full sun.
Choose a location where the water drains away instead of gathering. This shrub can handle acidic to slightly alkaline soils, but it does not like very rich soil, since this can hold too much moisture around the roots. A native to Mediterranean regions, this plant prefers relatively dry soil. Sandy or rocky soils are no problem.
In most regions, you will not need to water a chaste tree at all once it is established. In fact, you should avoid using organic mulches, since they hold too much water.
Temperature and Humidity
Vitex agnus-castus may be grown in Zones 6 to 9; it is technically hardy down to about minus-9 degrees Fahrenheit. But in zones 6, it often is grown more as a perennial plant rather than a shrub, since it may die back to the ground each winter, regrowing in spring. It does equally well in the high humidity of the Southeast U.S. as in the arid climate of the Southwest.
Chaste tree doesn't require much, if any, feeding. At most, a single application of a general-purpose balanced fertilizer every year or two will suffice.
Pruning Chaste Tree
You can encourage continued production by deadheading spent flowers—a task that can be a little irksome with larger shrubs. Yearly pruning during winter will help keep the shrub in an attractive shape and control its size. Chaste tree tolerates heavy pruning quite well. You can train a chaste tree into a small tree with a single trunk by pruning away completing shoots to encourage a central leader.
In colder climates, this plant is often pruned down right to the ground just before winter. Because it flowers on new wood, your chaste tree will return to a 3- to 5-foot flowering shrub each year, even with this fierce pruning routine.
Propagating Chaste Tree
The easiest way to propagate a chaste tree plant is by rooting some branch cuttings. As you might expect with such an easy-to-grow plant, Vitex roots quite easily.
Clip off a 12- to 18-inch branch tip, then cut off the flowering end portion. Also, remove the leaves from the bottom half of the cutting. Put the cutting into a vase of water, and set it in a location that receives morning sun but afternoon shade. (You can also root the cuttings by planting them in a container with moist potting soil.)
Over two months or so, the existing leaves will fall off the cuttings, but the other growth nodes will begin to bud and send out green growth. When the bottom of the cutting also begins to develop hair-like roots, the cutting can be transplanted into a pot or into a garden location.
Common Pests/ Diseases
Usually, the only problems you see on Vitex agnus-castus are root rots, nematodes, and leaf spots, though these are not common. Problems usually occur when the soil is not dry enough. Aphids, whiteflies, and scales may also attack, but they are usually easily controlled with horticultural soaps and oils.
Varieties of Chaste Tree
Several cultivars of chaste tree are widely sold:
- ‘Abbeville Blue’ grows 6 feet tall with a similar spread. It has deep blue flowers on 12- to 18-inch spikes.
- 'Alba' has white flowers. It is a large plant, growing to 15 feet with a 20-foot spread.
- 'Shoal Creek' is a 15-foot-tall plant with purple-blue flowers and leaves that have good resistance to fungal spots.
- 'Blue Puffball' is a great small shrub, growing only 3 feet tall with delicate blue flowers.
- 'Rosa Ann' is a 15-foot plant with heavily scented pink flowers.
Chaste tree is grown for its interesting, fragrant foliage and for the flowers that appear in late summer after most flowering shrubs have finished their display. It is commonly used in shrub borders, for foundation plantings, and in butterfly gardens—butterflies and other pollinators love the blooms.
In southern gardens, this plant is often used as an alternative to lilacs, which don't grow well in very warm climates. It is also a good choice for xeriscape gardens where irrigation water is used sparingly.