Chasteberry (Vitex agnus-castus)

Chasteberry, Chastetree, Chaste Tree, Lilac chastetree, Monk's Pepper, Texas lilac

Chaste trees, scientifically known as Vitex agnus-castus, are beautiful flowering trees that are exceptionally easy to grow and care for. With proper pruning they will repeat flower into early fall.

I. Appearance and Characteristics 

Vitex agnus-castus (also called vitex, chaste tree / chastetree, chasteberry, Abraham’s balm, lilac chastetree, or monk’s pepper) is a plant native of the Mediterranean region. It is one of the few temperate-zone species of Vitex, which is on the whole a genus of tropical and subtropical flowering plants.

Vitex agnus-castus is widely cultivated in warm, temperate, and subtropical regions for its delicately textured, aromatic foliage and butterfly-attracting midsummer spikes of lavender flowers opening in late summer in cooler climates. It grows to a height of 1–5 m (3–16 ft). It requires full sun, though tolerates partial shade, along with well-draining soil. Under ideal conditions, it is hardy to −23 °C (−9 °F) USDA Zone 6. In colder zones, the plant tends to die back to the ground, but as it flowers on new wood, flowering is not affected on vigorous growth in the following season. This plant is a brackish water dweller, indicating that it tolerates salt. Cold and wet weather results in dieback and losses. The plant grows well on loamy, neutral to alkaline soil.

In cultivation in the UK, the form V. agnus-castus f. latifolia has gained the Royal Horticultural Society’s Award of Garden Merit.

The fruits from one single tree can be harvested for more than 15 years. This indicates that the tree cannot be integrated in a usual crop rotation system. It is suggested to sow dissimilar plants such as monocots as its subsequent crop so that it might be easier to control the monk’s pepper plant, the dicot. Because the fruits of monk’s pepper tend to fall constantly and uncontrollably, the plant likely can germinate from seed. The overall best yield per hectare reportedly can be achieved if the plant spacing is around 70 cm (28 in). Pruning back the branches in autumn has a positive influence on fruit yield while repruning in spring can induce an increase of vegetative shoots, thus a fruit yield loss.

II. How to Grow and Care

Sunlight

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

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.

Watering

Chaste tree grow best with deep watering just after planting. During its first growing season, ensure that its root ball receives consistent moisture but avoid creating waterlogged or soggy conditions, which can result in root rot.

After it’s established, this Mediterranean native is quite drought-tolerant, appreciating watering during dry spells but not requiring it.

The ideal schedule is a thorough watering when the top inch of soil becomes dry. However, it’s vital to plant the chaste tree in well-drained soil to prevent water standstill around its root zone.

Overwatering is one of the main causes of its leaf spots and can lead the plant into winter dormancy in bad health. Ensure that you adjust watering as per your local climate and seasonal rainfall.

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.

Fertilizing

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.

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.2

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.

Propagation

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:

  • 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.
  • 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 hairlike roots, the cutting can be transplanted into a pot or to a garden location.

Potting and Repotting 

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:

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.

Line the planter with landscape fabric to prevent dirt from coming out of the holes.

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.

Pests and Diseases

Common Pests 

Aphids: One of the most common pests that plague the Chaste tree is aphids. These pests suck the sap from the foliage, weakening it and causing leaf spots. Aphid infestations can also lead to the new growth withering and turning yellow. You might notice a sticky substance (honeydew) on the leaves and fruit, attracting other insects, like sooty mold fungus.

Whiteflies: Whiteflies are another pest that might be seen in and around your Chaste tree. Similar to aphids, they too suck up the plant sap, causing a similar yellowing and wilting of leaves. The honeydew excretion they leave behind can also result in sooty mold growth.

Common Diseases

Root Rot: Root rot is a fungal disease which usually affects the Chaste tree under soggy conditions or when planted in poorly drained soil. The disease harms the root ball of the tree, impeding its ability to draw water and nutrients from the soil, leading to the foliage wilting and potentially plant death. It’s imperative that your tree is planted in well-drained soil to prevent this issue.

Leaf Spots: Leaf spots occur due to fungal or bacterial infections, often in high-humidity environments. They initially appear as small, dark spots on leaflets and can spread rapidly. This infection can potentially cause premature leaf drop which can be detrimental to the tree’s overall health and possibly affect the flowers’ color.

Common Plant Problems

Brown Tips

Brown tips on chaste trees can indicate a lack of water or exposure to extreme temperatures. The best solution involves moving the plant to a more suitable location, such as a place with well-drained soil and where it can bask in full sun or partial shade.

Yellowing leaves

Yellowing leaves, often accompanied by leaf spots, could signify a watering issue or a soil-borne disease like root rot. Twinned with soggy conditions and inadequate drainage, root rot is a significant risk. Therefore, ensure that it’s planted in rich soil that has excellent drainage to avoid this yellowing issue.

Failure to Bloom

If your chaste tree fails to produce its characteristic deep blue or pink flowers, it may be due to the lack of sun exposure or nourishment. If your plant is tucked away in a heavy shade or hasn’t been fertilized appropriately, it may refuse to bloom. These perennial plants enjoy full sun and a heaping of fertilizer in early spring to support the first flush of flowers.

Winter Dormancy

The chaste tree, like various shrubs, undergoes winter dormancy. This period can often lead to panic as the mature size plant sheds most of its leaves and appears lifeless. However, this is natural and requires no heavy intervention.

Overgrowth

Chaste trees, especially cultivars like Shoal Creek or Abbeville Blue, have an avid habit of new growth. They can spread readily if not pruned annually. You could maintain them as small patio trees or part of a shrub border, pruning the new wood after the second bloom to control their size.

Lack of Pollinators

Chaste trees, no matter their flowers’ color, are attractive to pollinators like butterflies. If you notice a lack of visits from these beautiful creatures, it might be due to a shortage of their preferred flowers. Establish a diverse array of blooms, including white flowers, lavender, and deep blue panicle flowers in your landscape, to attract a variety of pollinators.

III. Uses and Benefits 

Essential oils

Essential oils have been found in the fruits and in the leaves. The oil of leaves, unripe, and ripe fruits differ in compounds; 50 compounds were identified in the oil of unripe fruits, 51 compounds in the oil of ripe fruits, and 46 compounds in the oil of the leaves. 1,8-Cineole and sabinene are the main monoterpene components and beta-caryophyllene is the major sesquiterpene compound found in the fruits of V. agnus-castus. Some slight differences occur between fruits from white-flowering plants compared to violet-flowering ones. The oil of fruits of the former has a higher amount of monoterpene constituents. The leaves mainly contain 1,8-cineole, trans-beta-farnesene, alpha-pinene, trans-beta-caryophyllene, and terpinen-4-ol. The oil, particularly from white-flowering plants, is under preliminary research for its potential antibacterial effects.

Traditional medicine

Vitex has been used in traditional medicine for reproductive health issues in women, but only limited high-quality clinical evidence supports its effectiveness.

Although vitex is commonly recommended in Germany, V. agnus-castus should be avoided during pregnancy due to the possibility of complications.

IV. Harvesting and Storage

The flowering and ripening processes do not happen simultaneously, enabling harvesting of both fresh fruits and seeds over a long span of time. The fruits tend to fall from the plant as they ripen, getting lost in the soil. Thus, it has no optimal fixed harvest time. Consequently, to avoid yield loss, unripe fruits need to be harvested. This early harvesting has no effect on quality. Overall, harvesting the fruits by hand likely is the most convenient solution.

Chasteberry (Vitex agnus-castus) Details

Common name Chasteberry, Chastetree, Chaste Tree, Lilac chastetree, Monk's Pepper, Texas lilac
Botanical name Vitex agnus-castus
Plant type Shrub
Hardiness zone 7a, 7b, 8a, 8b
Growth rate Fast
Harvest time Fall
Height 8 ft. 0 in. - 20 ft. 0 in.
Width 8 ft. 0 in. - 20 ft. 0 in.
Sunlight Full sun (6 or more hours of direct sunlight a day)
Soil condition Clay
Flower color Pink
Leaf color Gray/Silver