verbena

​Verbenas are long blooming annual or perennial flowers that possess the virtues of heat tolerance and an extremely long bloom season. Many perennial verbenas are relatively short lived, but their vigor and heavy flowering make up for this defect. They do well grown as annual flowering plants also, since they bloom quickly during the first season after planting.

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Height/Spread
Verbenas vary considerably in size. The ground skimming moss verbena and trailing verbena reach 1 foot or less in height and spread from 2 to 5 feet wide. Verbena rigida usually grows 1 to 1½ feet tall, while purpletop vervain and the native blue verbena can reach 4 to 5 feet tall, but only a foot or two in width.
Growth Rate
Verbenas generally grow moderately to quickly, and unlike many perennials, bloom well the first season after planting. Some varieties, such as 'Homestead Purple', are extremely vigorous. If plants outgrow their assigned space, they tolerate trimming back well.
Ornamental Features
Verbenas are mainly grown for their remarkable length of bloom with most blooming from spring until close to frost if trimmed back once or twice in mid summer. Flower color ranges from white through pink, red, lavender, blue and purple.
Landscape Use
Verbenas require a location that receives full sun throughout the day. They must have well-drained soil. They will not tolerate overcrowding with poor air circulation, shade or soil that stays overly moist. Most problems of verbenas occur in improper growing conditions.

Verbenas are best planted in the spring or summer. Pinch the tips of the branches at planting time to encourage dense branching and a fuller plant. Newly planted verbenas will need to be kept moist for the first few weeks until the roots have spread into the surrounding soil.

While established verbenas are drought tolerant, performance, bloom, and growth rate will be reduced if they are too dry for a long period. During their blooming period, give them a thorough watering once a week if they do not receive an inch of rain that week. Avoid overhead watering.

If bloom slows during the summer, trim the whole plant back by about one fourth of its height and spread, water thoroughly and fertilize lightly. The plant will return to bloom within 2 to 3 weeks.

A light application of a complete fertilizer such as 16-4-8 in mid- to late spring and again after trimming back will revitalize plants, but additional fertilization is not generally required. Plants growing in very sandy, poor soil may need more frequent fertilization.

In the fall you can trim back verbenas lightly to give a neater appearance to the garden, but do not cut severely until spring as new growth begins to appear. Overly severe fall pruning can reduce cold hardiness and plants may not survive a cold winter. Most verbenas are short-lived, so you should plan on replacing them after two or three years. However, some species can re-seed and naturalize in the garden.

Verbenas, especially the trailing and moss types, grow very well in containers. Fertilize container grown plants either with a controlled-release fertilizer, or with a liquid fertilizer once a month. Container grown plants should be watered more frequently, and not allowed to dry out. All verbena will attract numerous butterfly species, bumblebees, and hummingbirds.

Problems
Verbenas can suffer from a variety of problems, but most occur when they are grown in low light, poorly drained soil, or when the soil stays excessively moist from excessive watering. Poor air circulation from over crowded conditions can also lead to disease problems.

• Powdery mildew appears as a white powder fungus on the surfaces of leaves. It most often infects verbena that does not receive enough sunlight, or is under stress from severe drought or other causes.
• Botrytis blight often occurs under overly moist conditions. Flowers turn brown and sometimes a gray, fuzzy fungus is visible.
• Root rot caused by Pythium or Rhizoctonia may occur in overly moist soil.

Verbenas are relatively pest free

• Aphids, whitefly, thrips, leaf miners and mites are the most common pests. Mites are most common in plants that are severely drought stressed.
• Snails and slugs are an occasional problem. They are worse during wet spells or if plants are heavily mulched.

Cultivars & Species
Tall growing
Purpletop vervain (Verbena bonariensis)

• This 4 to 5 foot tall species is sometimes called "verbena on a stick." Clusters of tiny lavender flowers appear above the tall, thin square stems in late spring and continue to bloom throughout the summer into fall. It is an excellent blender plant to fill in gaps in the back of the flower border, and will not crowd other plants because of its airy habit. Purpletop vervain is a short-lived perennial, but readily self-sows. It is drought tolerant. Cut plants back to encourage new blooms.
  
• Blue Vervain (Verbena hastata): This tall native species resembles V. bonariensis, but is much more tolerant of cold and moist soil, and the flowers are more blue-violet in color. Stems are branched with candelabra-like inflorescences. It is commonly seen growing wild along roadsides throughout South Carolina. Under garden conditions it appears neater than in the wild. Plants can vary from 2 to 5 feet tall or more, but can be trimmed back mid-summer if a shorter plant is desired. Some varieties have been selected for larger flowers and deeper blue flower color.
  

Trailing Verbena
(Glandularia canadensis; formerly Verbena canadensis)
Trailing verbena is a native perennial throughout South Carolina. The plants have a low spreading form and will flower profusely all summer. Creeping stems often root into the soil or mulch. Plants are tolerant of heat and drought, although best growth will occur with plenty of water and fertilizer. Like most verbenas, they need excellent soil drainage. There are numerous cultivars available. Many are trailing verbenas are hybrids of G. canadensis with other species.

• 'Homestead Purple' is one of the most popular trailing verbenas. It is a vigorous plant with large dark purple flower clusters. 'Homestead Purple' has excellent heat tolerance, deep green foliage and is a profuse bloomer from early spring until fall frost. Plants grow up to 3 feet wide and 1 foot tall. Discovered growing on an old Georgia homestead.
• 'Summer Blaze' has cherry red flower clusters from late spring through frost.
• 'Abbeville' is a vigorous variety with light lavender flowers, originally discovered growing near Abbeville, SC.
• 'Appleblossom' is a vigorous, long-flowering verbena with large flowers of cotton candy-pink with a contrasting white eye.
• 'Greystone Daphne' is one of the hardiest varieties of verbena, with fragrant pinkish lavender flowers. Begins flowering in very early spring, and continues until frost.
• 'Silver Anne' has warm pink flowers on vigorous plants. Sometimes incorrectly sold as 'Homestead Pink.'
• 'Taylortown Red' is a vigorous, heavy blooming red flowered cultivar.
• 'Snowflurry' is more upright than other trailing verbenas. It is a very strong plant, covered with white flowers.

Rigid Verbena
(Verbena rigida) This South American verbena forms spreading patches of brilliant purple. It is widely naturalized along roadsides throughout South Carolina. It spreads by long white rhizomes (underground stems) which spread out in all directions and form dense colonies. Because of this growth habit, it forms a very effective ground cover. Rigid Verbena is hardy and drought resistant.

• 'Polaris' is a silvery lavender flowered variety.
• 'Santos' grows to 12 to 18 inches tall with pinkish-purple blooms.
  

Moss Verbena
(Glandularia pulchella; formerly Verbena tenuisecta)
Native to South America, but naturalized throughout the southern United States, moss verbena is so well adapted as to be commonly believed to be native. It is generally hardy in the lower parts of South Carolina, and often survives mild winters in the Upstate. Moss verbena has finely cut leaves and a very low growing habit, explaining its common name. Many of the cultivars are hybrids with other species.

• Tapien Series includes a range of colors, including lavender, salmon, soft pink, pink, blue-violet, powder blue, and pure white. All have fine, lacy foliage and small flowers that cover the plant from early summer until the first frost. They are usually hardy in the lower parts of South Carolina, but are usually treated as annuals and replanted every spring. The Tapien series is resistant to powdery mildew.
• 'Edith' has fragrant lavender-pink flowers that cover a compact, long flowering plant.
• 'Imagination' is a well known purple variety that is very similar to the wild species.
• 'Sissinghurst' is a prolific bloomer with coral pink flowers from early spring until frost. The narrow cut-leaf foliage spreads rapidly to make a 3-4' mound in one season.
  

Annual Verbena
(Glandularia x hybrida; formerly Verbena x hybrida)
Annual verbena is a relatively common garden bedding plant. Most varieties will decline once summer heat increases. Perennial type verbenas will perform better in South Carolina, and will bloom quickly the first season of planting.

Source: Clemson University Cooperative University