How to Grow a Chaste Tree for Its Beautiful Purple Flowers

Vitex chaste trees are beautiful and virtually carefree summer-blooming shrubby trees that attract a wide variety of pollinators. It’s a fast grower that produces dense, upright panicles of flowers, up to 12 inches long, from late spring to fall. They are typically violet-blue but may be purple, pink, or white. Both flowers and leaves have a distinct spicy fragrance.

Hailing from Europe and parts of Asia, the chaste tree is most often grown as a large, multi-stemmed shrub but can be pruned to a single-trunk, 20- to 30-foot tree. Several varieties have a more compact size better suited to smaller gardens. It grows best in warm climates; in cooler regions (Zone 5 and 6) it is often grown as a perennial and cut back to the ground in winter. In spring, it quickly develops new shoots that grow 3 to 5 feet tall, producing, a spectacular flower show in summer. 

Where to Plant a Chaste Tree

This heat-loving plant needs full sun to grow its best. It prefers slightly acidic to neutral, well-drained soil. Because it grows as broad as it is tall, be sure to allow plenty of space. The chaste tree makes a spectacular lawn specimen, or several can be planted in a row along a driveway or property line. It is also effective as a background plant in a mixed sunny border garden.

How and When to a Plant Chaste Tree

Plant chaste tree in spring after the danger of frost has passed. The plants are late to leaf out and start growing, but once they do they grow rapidly. Thoroughly water the plant in its container before gently lifting it out. Loosen the roots with a claw tool or your fingers. Spraying the root ball with a stream of water will further loosen the feeder roots, allowing them to spread.

Dig a hole twice as wide and about the same depth as the root ball. If your soil is dense clay, add some compost to loosen it. Set your plant so that it sits at the same depth as it was growing in the container (or slightly above) and backfill the hole with soil. Tamp the soil as you go to eliminate air pockets. Water when the hole is half filled and again when the hole is completely filled.

Chaste Tree Care Tips

Once established, the chaste tree is nearly carefree. It has few pests and minimal disease issues. Depending on the look you’re after, annual pruning may be your biggest maintenance chore.

Light

Site your chaste tree in full sun, where it gets a minimum of 6 hours of direct sun each day. While it will grow with less sun, it will not flower nearly as well.

Soil and Water

Well-draining soil is critical for chaste trees. In consistently wet soil, roots will rot. If your soil is heavy clay, amend it with compost or choose a different site. These plants are moderately salt-tolerant.

Water regularly until your newly planted chaste tree is established, after which it usually will not need additional watering. It tolerates dry soil.

Temperature and Humidity

This is a heat-loving plant that also tolerates high humidity. It can survive winter temperatures to minus 9°F. However, in cooler regions, it may suffer winter dieback and is therefore often grown like a perennial that entirely grows back from its roots every year.

Fertilizer

Avoid over-fertilizing this plant because it will produce excessive foliage at the expense of flowers. A small amount of slow-release fertilizer sprinkled beneath its drip line every other spring should suffice. 

Pruning

Major pruning is best done in late winter. To prune as a multi-stemmed shrub, select four or five main trunks and clean out the center, removing most of the twiggy inner side branches, cutting them back to a main branch. To shorten a branch, cut back to a bud or side branch. If you would like to shape the shrub and allow space for planting beneath it, cut lower limbs back to a main branch.

To prune as a single-trunk tree, select the main trunk when the plant is young, removing side branches to the desired height before allowing upper branches to develop. Prune the crown of the tree as you would a multi-stemmed shrub, opening the center and removing twiggy growth back to main branches.

Alternatively, cut the entire plant back to the ground and let it resprout in spring. To encourage continuous flowering and discourage self-sowing, remove spent blooms.

Potting and Repotting

Small and compact chaste tree varieties are suitable for container growing. Just make sure that the container is large enough to accommodate the root ball and has large drainage holes. Excellent drainage of the potting mix is equally important.

Repotting the chaste tree to a larger pot with fresh potting soil is necessary every 2 to 3 years when the shrub outgrows its container.

Pests and Problems

The chaste tree is rarely troubled by pests. Thrips, aphids, scale insects, and whiteflies occasionally appear, but can usually be controlled with a hard spray of water or insecticidal soap.

Few diseases bother this shrub unless it is growing in a soggy location where root rot can occur. Avoid such sites, or improve the soil drainage.

How to Propagate a Chaste Tree

Chaste trees root easily from softwood cuttings taken in late spring or early summer. Take cuttings four to six inches long, remove any flower buds and the bottom leaves. Dip the ends into rooting hormone and insert the cuttings into pots filled with wet sand or perlite and cover them with a plastic tent.

Keep the growing medium damp but not soggy. After about 6 weeks, roots should form. If more than one cutting has rooted, transplant the extra cuttings to separate containers.

The chaste tree reseeds itself freely so you might find volunteer seedlings near your plant. Dig them up and transplant them in a suitable location or a pot.

To start a chaste tree from seed, collect and extract the seed from mature fruit in the fall. Plant it in a container filled with well-draining soil, water it, and leave it outdoors over the winter. After the seeds have germinated, transplant the seedlings to a larger container in the spring.

Types of Chaste Tree

Selections vary in size and flower color. Newer more compact varieties are better suited to smaller landscapes.

‘Shoal Creek’

This cultivar with a shrubby, multi-stemmed growth habit grows 10 to 15 feet tall and up to 12 feet wide and bears large, blue-violet flowers.

‘Alba’

Growing 10 to 15 feet tall and up to 20 feet wide, this variety produces an abundance of white flowers in late spring or summer.

‘Rock Steady’

More compact than other varieties, ‘Rock Steady’ grows only 4 to 12 feet tall and 4 to 5 feet wide. It produces non-stop lavender blooms over a very long season.

‘Pink Panicle’

This variety bears medium pink blooms on compact 4- to 8-foot plants. 

‘Blue Puffball’

Another smaller selection, ‘Blue Puffball’ bears sky blue flowers on mounded plants that reach 4 feet tall and wide.