The Caryopteris genus is made up of seven species of low-maintenance, late-flowering shrubs to liven up your autumn landscape. These aromatic plants are covered with blooms in shades of true blue from late summer up until the first frost, with a few cultivars flowering in white and purple. The small dome-shaped shrubs are valued for finely textured foliage including green, silvery gray, golden, reddish-purple, or variegated color depending on the type.
I. Appearance and Characteristics
Caryopteris (bluebeard; Chinese: 莸属 you shu) is a genus of flowering plants in the family Lamiaceae (formerly often placed in the family Verbenaceae). They are native to east Asia (China, Korea, Japan, Mongolia).
They are herbaceous plants or small shrubs growing to 1–4 m tall. The leaves are opposite, simple ovate to lanceolate, with an entire or crenate margin; they are often aromatic. The blue or white flowers are pollinated by butterflies and bumblebees. The fruit is a four-valved capsule containing four seeds.
Though several Caryopteris species are grown in botanical gardens, as ornamental plants the species have largely been superseded in gardens by the hybrid Caryopteris × clandonensis (C. incana × C. mongholica). The accidental cross that produced it occurred in the garden of Arthur Simmonds at Clandon, near Guildford, Surrey. In 1930, wishing to propagate C. mongholica, he gathered seeds from a plant that was growing near C. mastacanthus. When the seedlings eventually flowered in their second year, hybrids appeared. The final selection, however, was made of a self-sown volunteer that appeared under C. mastacanthus, and eventually smothered it. It began winning Royal Horticultural Society medals in 1933. This small, deciduous, aromatic shrub has grey-green leaves and produces masses of blue flowers in late summer.
Caryopteris × clandonensis, an unusual plant in American gardens in the 1960s, has become more familiar there, especially in xeriscaping.
Like Buddleja, the woody stems can die back in the winter, particularly in colder climates and on heavy soils. They prefer well-draining, sandy soil in full sun, but does not need especially rich soil or constant moisture.
Leaves and herbaceous stems have a terpene aroma like eucalyptus, especially when lightly bruised.
II. How to Grow and Care
Sunlight
Caryopteris needs full sun at least six hours daily. Planting in the shade leads to thin foliage and a dearth of flowers.
Termperature and Humidity
Caryopteris is heat- and drought-tolerant once established, but extended periods of temperatures above 90 degrees Fahrenheit create a need for more frequent watering. The ideal temperature is from 65 to 85 degrees Fahrenheit. Roots are cold hardy to zone 5 with top growth dying back during cold weather. Top growth is hardy to zone 7, however many gardeners choose to go ahead and cut the shrubs back at the end of the bloom period. Protect roots with a 3-inch layer of mulch in areas where temperatures dip to 20 degrees Fahrenheit.
Watering
Water young plants regularly when the top 2 inches of soil are dry to support root development. These plants mature fairly quickly, often reaching full height of 2 to 3 feet in one season and are fairly drought tolerant once established.
Soil
This shrub does not tolerate soggy soil which causes root rot. Neutral, well-draining loam is the preferred soil type ranging from slightly acidic to slightly alkaline with pH levels of six to eight.
Fertilizing
Fertilizing caryopteris is optional and plants respond better to organic soil amendments than to inorganic products. To give young shrubs a boost, apply a balanced fertilizer such as an NPK 10-10-10 in early spring. For a more suitable alternative work aged compost, garden, or potting soil into the planting hole.
Planting Instructions
Caryopteris is usually planted in spring but can be planted in autumn in warmer regions. Spring planting should take place after all danger of frost has passed. For autumn planting, set caryopteris out about four weeks before the first frost.
Dig a hole approximately twice as wide as the root ball and deep enough so the crown rests at the same level as in its original pot. Then place the shrub in the planting hole feathering out the roots. Backfill the soil, lightly tamp down, and water well. If you are planting more than one caryopteris, space shrubs about two feet apart.
For growing in pots, choose a container at least twice as wide as the rootball with good drainage holes. Fill it with a combination of high-quality potting mix, compost, and sand. Plant the caryopteris following the directions above. Potted plants need more frequent watering and benefit from regular feeding with a balanced liquid fertilizer.
Pruning
Caryopteris blooms on new wood so pruning is done after the bloom period has ended in autumn or in early spring before new growth begins. Cold tolerance of the top growth depends on variety and growing zone but many gardeners choose to prune caryopteris back to ground level in autumn to allow for new growth in spring.
Prune old and damaged wood from the center of both in-ground and potted plants in early spring before new growth appears. Gentle trimming can be done to maintain a pleasing shape throughout the growing season, but heavy pruning significantly reduces the number of flowers later in the season.
Propagation
Softwood stem cuttings are the easiest method for propagating caryopteris. It can be grown from seed collected dry in autumn then surface sown and given a period of cold dormancy. However, since most cultivars are hybrids, increasing your collection with softwood cuttings is more reliable and best accomplished in summer. You’ll need a hand pruner or snip, small pots, rooting hormone, and potting mix. Follow these steps.
- Use the pruner or snip to remove a 6-inch green stem from the terminal end of a branch, cutting just above a leaf node.
- Remove all but the top set of leaves.
- Fill the pot/s with moistened, loose, well-draining potting mix.
- Use your index finger or a pencil to make a narrow, deep hole in the center of the pot.
- Dip the bottom portion of the cutting in the rooting hormone. Caryopteris will form roots between leaf nodes,
- Insert the cutting into the hole in the center of the pot and firm the soil around it.
- Water gently but thoroughly and place in a sunny location.
- Roots should form in seven to 10 days. Give the cutting a gentle tug to check for resistance which indicates roots have developed.
Potting and Repotting
Bluebeard works beautifully in containers and makes a lovely addition to sunny patios or decks, but container-grown plants may need more care than those grown in the ground.
When growing bluebeard in a container, make sure to choose a container with excellent drainage that is large enough to accommodate the mature size of the cultivar you selected. Fill the container with a rich potting mix (that has a neutral pH) and incorporate some organic compost. This will help aerate the soil, so it accepts and stores water more efficiently. Make a space in the potting mix larger than the plant’s root ball and add the plant to the container so the crown of the roots sits at the same level as it did in its old pot. Fill in the space with a potting mix and water the plant thoroughly.
Plan to water your container-grown bluebeard whenever the top 1 to 2 inches of soil feel dry. Feed your plant with a water-soluble fertilizer every few weeks beginning in the spring and continuing throughout the growing season.
When winter comes, reduce watering and consider moving your potted bluebeard into an unheated, protected area (like a garage or shed) where it will be safe from the elements. You can move it back outside after the danger of frost has passed.
Bluebeard plants tolerate transplantation, so if you need to move yours to a larger container, the best time to do so is in early spring or the cooler (but not cold) months of fall.
Overwintering
Caryopteris roots are cold hardy to USDA zone 5 but a layer of mulch can help protect them when temperatures drop below 20 degrees Fahrenheit. If you experience especially harsh winters you may want to plant in a protected location. Move pot-grown shrubs into an unheated garage, basement, or porch. When overwintered indoors as a houseplant, the plant goes into dormancy and loses all its foliage.
Pests and Diseases
Common Pests and Plant Diseases
Caryopteris is relatively free of both pests and plant disease. Depending on where you live, your shrubs may attract pests or fungal diseases endemic to your specific environment.
Infestations are rare and the only real issue to guard against is root rot. Avoid overwatering, plant in a sunny location with well-draining soil, and choose containers no more than twice the width of the rootball. Cedar and cypress mulches emit oils that insects don’t like so choose these materials to keep roots hydrated and healthy.
Common Problems
The most common problem with caryopteris is wilting due to oversaturated roots. Amend heavy clay soils or plant in a location with loose well-draining soil. Avoid overwatering established plants by irrigating when the soil is dry to a depth of 5 inches. Young plants should be watered when the top 2 inches of soil is dry. Check the soil for moisture since wilting can be a sign of both under and overwatering.
III. Uses and Benefits
Grown for its stunning purplish-blue blossoms, bluebeard (Caryopteris) adds a much-needed splash of garden color from mid to late summer in Zones 4 through 9. The easy-care shrub carries its spectacular display through much of the fall, mixing well with cool color palettes and acting as a refreshing contrast to the hot colors of fall.
