Chaste tree (Vitex agnus-castus) is a deciduous shrub that bears clusters of purple flowers in the summer. Also known simply as vitex, the leaves of this plant are 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 (panicles) that bloom in midsummer look like those of the butterfly bush (Buddleja spp.) The black fruit contains four seeds that look like peppercorns and are sometimes used to flavor food.

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, but most gardeners opt to keep this potentially invasive plant to 10 feet or less in height.

Chaste Tree Care

This 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 chaste tree is that it may grow too aggressively, requiring frequent pruning to keep it in check.

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.

Light

Chaste tree will grow well in full sun to part shade, though the best flowering occurs in full sun.

Soil

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.

Water

In most regions, you will not need to water a vitex 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, where it often dies back to the ground each winter, regrowing in spring. It does equally well in the high humidity of the southeastern United States as in the arid climate of the Southwest.

Fertilizer

A 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. For the amount to use, follow product label instructions.

Types 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.
• 'Rosea' is another pink-flowered cultivar, growing to 15 feet.

Smaller cultivars for potting include 'Blue Diddley' (grows to 6 feet) and 'Pink Pinnacle' (grows to 4-6 feet).

Pruning

Left unpruned, chaste tree can become a sprawling, vase-shaped shrub that sometimes grows to 20 feet or more with a spread equally as wide. It is sometimes trained as a single-trunk small tree by pruning away competing shoots to encourage a central leader. Early 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 encourage continued production by deadheading spent flowers—a task that can be a little irksome with larger shrubs. Aggressive deadheading often produces a second flush of flowers about six weeks after the first.

In colder climates, this plant is often pruned down 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 is by rooting some branch cuttings. As you might expect with such an easy-to-grow plant, chaste tree roots quite easily:

1. In early summer, clip off a 12- to 18-inch branch tip using sharp pruners, then cut off the flowering end portion. Remove the leaves from the bottom half of the cutting.
2. 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.
3. When the bottom of the cutting also begins to develop hairlike roots, the cutting can be transplanted into a pot or to a garden location.

Growing Chaste Tree From Seed

The seeds found within the fruits will readily sprout up wherever they fall in the garden, and these volunteers can easily be transplanted into new locations. Or you can collect ripened fruits, extract the seeds, and plant them where desired.

Potting and Repotting Chaste Tree

Growing a smaller cultivar of chaste tree in a pot is easy. Smaller cultivars grow only 3 to 6 feet. You can keep the tree in the same pot for a few years before any repotting is necessary. Follow these simple steps:

1. Measure the root ball of the tree, then choose a container that is at least 8 inches larger in diameter than the root ball. The planter should have several drainage holes.
2. Line the planter with landscape fabric to prevent dirt from coming out of the holes.
3. Blend a good quality, well-draining potting mix with about 10 percent perlite, then pot up the plant.

Overwintering

In the landscape, chaste tree usually requires no winter protection if grown in its recognized hardiness range. In zone 6 (and sometimes even zone 5), some gardeners grow chaste tree as a perennial plant, cutting it back to ground level each winter and allowing it to sprout back each spring. It generally will put on 3 or 4 feet of growth and reach flowering maturity each season.

Common Pests & Plant 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.

This plant needs well-draining soil, and if grown in soggy conditions, it may experience fatal root rot.

How to Get Chaste Tree to Bloom

Chaste tree normally has a long bloom season that can begin in early summer and continue into September. Within this period, there are peak bloom periods that repeat themselves if the spent flowers are deadheaded. If your chaste tree fails to bloom as robustly as you expect, it's likely because the plant is not getting enough sunlight. Another hindrance is excessive fertilizer. In most soils, this plant will require no additional feeding; fertilizer sometimes reduces flowering by stimulating green growth at the expense of blossoms.

Common Problems With Chaste Tree

This is a remarkably easy plant to grow, but some homeowners become annoyed with its messiness. The summer fruits can stain pavement or lawn furniture, and the prolific self-seeding requires constant plucking of volunteer plants to keep them from spreading. In fact, some gardeners eventually remove the plant altogether due to this invasive behavior.