How To Grow And Care For Chaste Tree

A summer-blooming favorite.

Chaste tree. vitex.jpg
Photo:

Photo by Steve Bender

Native to southern Europe and central Asia, the chaste tree quickly grows into a multi-trunked tree about 10 to 20 feet tall and wide with a broad, spreading habit, making it invasive in some environments. Also known as "monk's pepper," its name comes from the erroneous medieval belief that a potion made from it could curb libido. The chaste tree (Vitex agnus-castus) does stand up to dry spells in the summer heat and grows just about anywhere. 

The best thing about the chaste tree is the flowers, which bloom in upward-growing panicles up to a foot long. Chaste tree is one of the few winter-hardy trees with blue flowers (although they can also be pink, purple, or white). These plants also produce black fruit the size of a peppercorn. Shrubs are best planted in the spring to establish their roots before winter dormancy. When purchasing an unnamed chate tree from a nursery, buy it in bloom so you can see the flowers' color and the plant's general shape.

Plant Attributes

Plant Attributes
 Common Name:  Chaste Tree, Vitex, Lilac Chaste Tree, Monk's Pepper Tree
 Botanical Name:  Vitex agnus-castus
 Family:  Lamiaceae
 Plant Type:  Perennial, Shrub
 Mature Size:  3-20 ft. tall, 3-20 ft. wide
 Sun Exposure:  Full
 Soil Type:  Clay, Well-drained
 Soil pH:  Acidic to Neutral (6.0 to 7.0)
 Bloom Time:  Summer
 Flower Color:  Pink, Blue, Purple, White
 Hardiness Zones:  Zones 6-9 (USDA)
 Native Area:  Europe, Asia

Chaste Tree Care

Plant chaste trees as a single specimen on the lawn, in a row along a property line or driveway, as a small patio tree, or on a border with lower plants growing beneath it. This shrub is easy-to-grow but requires pruning as its spreading character makes it invasive if left unchecked. 

Chaste trees require full sun exposure and are usually winter-hardy in USDA Zones 6 to 9. In Zones 5 and 6, the chaste tree may die back to the ground in winter, then sprout and bloom the following summer. Chaste trees attract all kinds of pollinating insects and birds. Bumblebees love this plant above all others and will even spend the night on the flowers.

Light

Chaste trees grow best in full sun, at least six hours daily. This plant will tolerate partial shade but will not flower as heavily.

Soil

Chaste trees thrive in slightly acidic to neutral soils that are well-draining. Choose a location that does not contain too rich nutrients, preferring dry or clay soils to moist environments. Chaste trees grow in sandy and rocky regions because it is relatively drought-tolerant once established.

Water

Water deeply into the root ball when first establishing the chaste tree. Afterward, most chaste trees are drought-tolerant and will not require additional watering. Avoid organic mulches or rich soil that retains too much moisture.

Temperature and Humidity

Typically grown as perennial, chaste trees tolerate high heat and are cold-hardy to -9°F. Chaste tree shrubs go dormant throughout the winter and regrow in the spring. Humidity is rarely an issue as it thrives in arid climates. Strong winds are not too much of a concern.

Fertilizer

Avoid organic material as it retains too much moisture. Adding a slow-release general-purpose fertilizer every year or two can help keep shrubs healthy. Too much fertilizer can cause excessive foliage growth.

Types of Chaste Trees

Chaste trees are available in several cultivars. Selections have a range of colors and sizes, depending on your preferences. Here are a few varieties to know: 

  • 'Abbeville Blue': This selection grows six feet tall and wide, bearing deep blue panicle flowers in the summer, reaching 12 to 18 inches long. 
  • 'Alba': Bears white flowers reaching a mature height of 10 to 15 feet and 15 to 20 feet wide.
  • 'Blue Puffball': This selection grows only three feet tall and four feet wide, making it a smaller variety to grow as a shrub in compact spaces. It bears deep blue flowers.
  • 'Rosa Ann': A fragrant selection with pink flowers reaching eight to 15 feet tall and 10 to 15 feet wide.
  • 'Shoal Creek': A common variety, this chaste tree reaches 10 to 15 feet tall and 15 to 20 feet wide. It bears large, blue-violet flowers.

Pruning

Chaste trees are not the tidiest plant in the world, and it needs regular pruning to produce an attractive multi-trunked tree. Prune in winter by cleaning out the entire center of the tree and removing all side branches from the main four to five trunks. Also, remove messy, twiggy growth that tends to crowd the ends of the branches. Another option, cut the entire plant to the ground in winter. It will sprout in spring and bloom in summer, although later than chaste trees not pruned so severely. You can also force a second bloom in summer by removing the first flush of flowers as soon as they fade. Clean up fallen berries to avoid seedlings popping up around your yard.

Propagating Chaste Trees

Chaste trees propagate quickly through cuttings. Here is how:

  1. Take softwood cuttings at least four to six inches long in late spring or summer. Cuttings should be flexible but not break. Use a sharp, sterile knife or pruning shears to snip the flowering end. Remove all the bottom leaves, leaving only a few leaves towards the top of the cutting. 
  2. Fill a container with moist, coarse sand, ensuring proper drainage. 
  3. Dip the end of the softwood cuttings into a rooting hormone and place it directly into the container filled with coarse sand. Use a pencil or your finger to make deep enough holes, so the bottom of the cutting is completely covered.
  4. Use a plastic bag to cover the container and increase the humidity. Place the entire container in a sunny location and keep the sand moist. 
  5. In about four to six weeks, gently tug cuttings to check if roots have emerged. Previous leaves will fall off as new nodes or buds show green growth.
  6. After roots establish, transplant the cuttings into a larger container or outdoor location with moist, well-draining soil.

How to Grow Chaste Trees From Seed

Collect seeds from chaste tree fruits or a garden center. Seedlings sprout from fall fruit, so pick them up to prevent unwanted growth or spreading. After extracting seeds from the fruit, press them into moist potting soil and place the container or seed-starting tray in direct sunlight. Seeds need full sun and moist soil for germination. After two weeks of care, seedlings will emerge. Transplant seedlings once it reaches a few inches tall and the threat of the final frost has passed. When starting seeds indoors, begin about a month before the last frost.

Potting and Repotting Chaste Trees

Depending on the size of the chaste tree, repotting might be necessary to ensure the roots have enough space to spread. Containers should be at least eight inches larger in diameter than the root ball, providing at least two to three years of growth before transplanting is needed. Choose a container with plenty of drainage holes and fill it with potting mix and perlite. 

Overwintering

Chaste trees only require a little winter care as they will die back every year and regrow in the spring when grown as a perennial. Cut the trunk to the ground and mulch around the roots to protect it from the cold and preserve moisture. Chaste trees tolerate some frost but should move indoors if growing in containers. Keep containers in a cold environment to prevent unwanted budding.

Common Pests & Plant Diseases

Chaste trees are relatively pest-free, but thrip, aphids, whiteflies, and scales occasionally attack—control pests by spraying the tree with a hose in the morning or using insecticidal soap. Don't leave foliage wet. Soggy conditions promote other fungal infections like root rot and leaf spots.

How to Get Chaste Trees to Bloom

Removing spent blooms can encourage a second showing of flowers on chaste trees. Proper care, including enough sunlight exposure, avoiding over-fertilization, and maintaining healthy soil, will promote showy blooms.

Common Problems With Chaste Trees

Chaste trees spread quickly and have self-seeding proliferation that can cause them to be invasive if left unchecked. While relatively easy to maintain, a chaste tree still has some issues to be aware of if growing this plant in your yard or garden:

Leaves Turning Black/Brown 

Leaf spot is a fungal infection that causes brown or black spots to emerge throughout the foliage. The spots will form in patches, often with a yellow-edged appearance. Prevent leaf spots from spreading by removing diseased foliage, raking up fallen leaves, and avoiding wet foliage. Always water at the plant's base and use a fungicide if necessary. 

Leaves Turning Yellow

Pest infestations, such as scales or mealy bugs, can cause foliage to weaken as they remove the sap. Additionally, these pests often produce a honeydew substance creating a sooty mold that causes a fungal growth on the bark. Weak foliage turns leaves yellow and causes them to drop. Remove infested foliage and try using insecticides to prevent spreading.

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