This wildflower grows in prairies across the US and Canada. It attracts bees, birds, and butterflies, and provides a home for Common Buckeye caterpillars. Blue vervain has been used in traditional medicines in a variety of cultures but has been found by modern science to have negative effects on the human body under some conditions.
I. Appearance and Characteristics
Verbena hastata, commonly known as American vervain, blue vervain, simpler’s joy, or swamp verbena, is a perennial flowering plant in the vervain family Verbenaceae. It grows throughout the continental United States and in much of southern Canada.
V. hastata grows as a stiffly erect stem, occasionally branching in the upper half, reaching up to 1.5 m (5 ft) tall. The stems are four-angled (square), hairy, and green to reddish in color. Leaves are opposite, simple, and measure up to 15 cm (6 in) long and 3 cm (1 in) across. They have doubly-serrated margins and a variety of shapes, from lanceolate to ovate, and may have 2 lateral lobes.
The inflorescence is a panicle, or group, of flowering spikes, up to 30 cm (1 ft) long at the end of the upper stems. Each flowering spike in the panicle is up to 13 cm (5 in) long, with densely packed, numerous 5-lobed flowers, which measure up to 1 cm (0.25 in) long. The flowers are violet or deep purple, rarely white. They open from the bottom of the spike upward, with only a ring of a few flowers open at a time.
The flowers bloom from mid- to late summer.
It attracts bees and is a larval host to the common buckeye butterfly (Junonia coenia), the verbena moth (Crambodes talidiformis), and the verbena bud moth (Endothenia hebesana).
II. How to Grow and Care
Sunlight
For the small clusters of flowers to maintain their bright colors in pink, yellow, and purple, the blue vervain must have plenty of sunlight. While you can grow it in a slightly shaded area, it is recommended that the blue vervain has a minimum of six hours of sunlight each day. Any less than this and your flowers may be dull in color.
Temperature
Native to Northern America, Asia and Europe, the blue vervain is a hardy plant. While it can survive in temperatures between 14 to 19 ℃, it prefers temperatures between 20 to 26 ℃ to encourage an abundance of flowers. While it is technically a perennial, some find it easier to grow the blue vervain as an annual plant, depending on location and variety.
Watering
Blue vervain needs consistent watering throughout the spring and summer but will require less in fall and winter. Pay close attention to your plant and never miss a watering – the blue vervain will struggle to recover from bouts of neglect.
Ideally, you should check on your plant every single day in hot weather. If the soil is dry or the plant is starting to wilt, then it needs a drink! A good tip is to water your plant in the morning at its base rather than on the flowers. This is because a strong stream of water could damage the delicate petals.
Soil
While the blue vervain is not too fussy about what type of soil it is planted in, it does need to be in a well-draining one. For example, loamy soil with a PH value of 6-7 (so slightly acidic) would be absolutely ideal. If possible, choose a soil that is fertile and rich in nutrients, but not one that is heavy, such as clay.
Fertilizing
The blue vervain needs lots of feeding to ensure a healthy and colorful plant. Use an organic water-soluble fertilizer and apply this directly to the soil. This is because the fertilizer may burn the leaves or flowers if it comes into contact with them.
Feed your blue vervain twice a month in the spring and summer. Some also choose to feed their plant once a month in the fall and winter seasons too.
Planting Instructions
The blue vervain is very adaptable to where it is planted, whether this is in containers, borders, or even hanging baskets. It is advisable to plant it in the ground rather than in a container. This is because planting the blue vervain in the ground gives its roots a better chance to settle.
When planting your blue vervain, space seedlings at least 30 cm apart, although more room may be needed for the larger varieties. This is to make sure that the roots have enough space to support the plant.
To plant the seedlings, dig a hole that is twice the size of their root ball and just deep enough for the bottom of the stem to be below soil level. After that, it would be a good idea to mix in some organic compost before planting your blue vervain. This will help the plant to settle while improving drainage to prevent root rot and encourage it to settle. You should aim to plant your blue vervain at the beginning of spring, before the blooming season.
Pruning
Depending on the variety of blue vervain, it can grow between 10 to 140 cm in height and 2 m wide in its spread.
The blue vervain will bloom from the beginning of summer until the middle of winter, when the first frost arrives. Because of the plant’s large amount of bloomage, it can quickly start to look a little disheveled if not pruned regularly. To avoid this, prune every month in the summer. Throughout the rest of the year, consider pruning your blue vervain twice each season if it requires it.
During summer, when the plant is in bloom, trim back any spent flowers or withered foliage. If regularly pruning, trimming back by 2.5 to 5 cm each time will help to maintain your plant’s shape. Also, pinch tips to encourage more abundant blooms in other areas of the plant. Avoid removing over a third of the plant overall, as this may affect flowering in the future.
Propagation
While you can propagate your blue vervain from cuttings in the spring, it is easy to propagate this plant from seeds purchased from a garden center. Be aware that it can take a long time for the plant to flower from a seed – up to 90 days.
Plant your seeds in 5 cm of soil in a cool indoor area around ten weeks before the end of winter. After two weeks, you should start to see your blue vervain sprouting. Once the seedlings reach 5 to 8 cm, harden them off before planting. To harden your seedlings, begin by leaving them outdoors for an hour on the first day. Then, increase how long they are left outside by an hour each day for a week. By now, they should be ready to be planted outdoors.
Overwintering
As V. hastata is native to wetland regions experiencing cool winters, it need not be brought indoors as temperatures drop. Instead, prepare the base of the plant for winter by cutting down the shoot. This will naturally die back if left uncut once temperatures begin to drop. The plant should naturally enter a dormant state that can be sustained as long as temperatures don’t drop severely. You may opt to mulch the crown to protect the roots from temperature fluctuations.
Despite its preference for moist substrates, swamp verbena should be watered sparingly throughout winter. Excess moisture in the cold may damage its root system. Resume regularly watering the plant in spring, when new growths should begin to appear.
Pests and Diseases
It isn’t uncommon for plants to face certain threats when growing in any planting location. Blue vervain is no different.
When growing blue vervain, it’s common to deal with specific pests and diseases. The main diseases you may face are root rot, leaf spot, and powdery mildew.
These are fungal based issues that can typically be treated with a fungicide. However, root rot may not be treated with a fungicide.
Instead, if you suspect this disease, you must dig up the plant at the roots and allow them to fully dry before transplanting in an area with better drainage.
In most cases, the plants don’t survive. The best way to beat fungal disease is to deter it. Fungal disease thrives in areas with cold, wet soil.
To keep it away, be sure to plant your flowers in full sunlight. Though these plants prefer cooler temperatures and damp soil, ensure the soil drains adequately. You don’t want the plant left in standing water.
Powdery mildew may be treated with a fungicide and also by planting in areas with appropriate growing conditions.
However, ensuring you prune the flowers or divide them when they’re becoming overcrowded could help with this disease as well.
When the plants are provided adequate airflow, it makes it easier for damp areas to dry and less likely that fungal issues will develop.
You may also try watering your flowers in the morning instead of at night. This will give them ample time to dry throughout the day to deter fungal disease.
The most common pest to impact this flower is the whitefly. There are two common ways to treat them. The first option is to apply an insecticide, and the second option is to apply soapy water to your plants and spray them forcefully.
The soap will kill the whiteflies while the forceful water will dislodge any remaining pests and their homes from your plants.
Take these tips into consideration when growing a blue vervain plant. It’s vital that you remain alert to these threats to ensure your plants receive little to no harm should they face these diseases or pests.
III. Uses and Benefits
A water-loving flowering perennial chosen by gardeners for its beauty, hardiness, and ability to grow in waterlogged areas, blue vervain is a natural choice for rain gardens or any sunny, boggy spot in your garden. It looks great in meadow gardens, and is often used as a border plant.
