Common mullein (Verbascum thapsus) has been cultivated by farmers and gardeners since colonial times. This herb has a thick stem and leaves covered with a layer of “fur” that feels like flannel. Today, it grows wild in many areas of the U.S., including roadsides and vacant lots. Flowers of common mullein are occasionally brewed into tea.
I. Appearance and Characteristics
Verbascum thapsus, the great mullein, greater mullein or common mullein, is a species of mullein native to Europe, northern Africa, and Asia, and introduced in the Americas and Australia.
V. thapsus is a dicotyledonous plant that produces a rosette of leaves in its first year of growth. The leaves are large, up to 50 cm long. The second-year plants normally produce a single unbranched stem, usually 1–2 m tall. In the eastern part of its range in China, it is, however, only reported to grow up to 1.5 m tall. The tall, pole-like stems end in a dense spike of flowers that can occupy up to half the stem length. All parts of the plants are covered with star-shaped trichomes. This cover is particularly thick on the leaves, giving them a silvery appearance. The species’ chromosome number is 2n = 36.
On flowering plants, the leaves are alternately arranged up the stem. They are thick and decurrent, with much variation in leaf shape between the upper and lower leaves on the stem, ranging from oblong to oblanceolate, and reaching sizes up to 50 cm long and 14 cm across (19 inches long and 5 inches wide). They become smaller higher up the stem, and less strongly decurrent down the stem. The flowering stem is solid and 2–2.5 cm (nearly an inch) across, and occasionally branched just below the inflorescence, usually following damage. After flowering and seed release, the stem and fruits usually persist in winter, drying into dark brown, stiff structures of densely packed, ovoid-shaped, and dry seed capsules. The dried stems may persist into the following spring or even the next summer. The plant produces a shallow taproot.
Flowers are pentamerous with (usually) five stamen, a five-lobed calyx tube, and a five-petalled corolla, the latter bright yellow and an 1.5–3 cm (0.59–1.18 in) wide. The flowers are almost sessile, with very short pedicels (2 mm, 0.08 in). The five stamens are of two types, with the three upper stamens being shorter, their filaments covered by yellow or whitish hairs, and having smaller anthers, while the lower two stamens have glabrous filaments and larger anthers. The plant produces small, ovoid (6 mm, 0.24 in) capsules that split open by way of two valves, each capsule containing large numbers of minute, brown seeds less than 1 mm (0.04 in) in size, marked with longitudinal ridges. A white-flowered form, V. thapsus f. candicans, is known to occur. Flowering lasts up to three months from early to late summer (June to August in northern Europe), with flowering starting at the bottom of the spike and progressing irregularly upward; each flower opens for part of a day and only a few open at the same time around the stem.
II. How to Grow and Care
Sunlight
Mullein thrives in full sun. Plant them in a dry, warm spot near walls or large trees to protect them from wind.
Temperature and Humidity
Common mullein is a tough plant that can withstand extremes at either end of the temperature spectrum. It is hardy down to -25 degrees F and will thrive throughout a hot summer if watered occasionally in the absence of rain. It is not finicky about humidity levels.
Watering
Keep the soil moist when growing mullein from seed. While the plant doesn’t need much moisture, water more often as it starts to flower.
Soil
Grow mullein in just about any type of soil, preferably soil that is dry and slightly alkaline. The plant will also adapt to poor, calcareous soil. Being so adaptable, it can spread quickly, creating dense patches even faster than some native plants.
Fertilizing
Mullein can grow faster and produce more flowers when fed with a low release 10-10-10 fertilizer. For the amount to use, follow product label instructions.
Pruning
Propagation
Propagate mullein from seeds and cuttings. Either buy seeds or collect seeds from plants as soon as the fruits are borne from flowers.
Mullein, with its deep taproot, can also be propagated through root cuttings when the plant is dormant in late fall to early spring. Here’s how:
- You will need a shovel, sharp knife or pruners, potting soil, and a starter pot.
- With a shovel, dig up a mullein plant around it’s base to expose its roots.
- Choose a root near the center crown of the plant, and with a sharp knife, cut across the root.
- For deep vertical root cuttings, trim down from the top where it was cut from at the crown so the root cutting is a few inches long.
- Plant in well draining, potting soil with a top that was cut near the crown right side up.
- Keep in full sun with moist soil and transplant to the garden once a true set of leaves start to form.
How to Grow from Seed
Seeds usually fall just a few feet away from the parent plant, blown down by the wind or shaken down by an animal. None are known to disperse long-distance. Seeds can remain alive and viable for decades in the soil. Seeds that are on the surface or just below it will have enough light to germinate. So the more the soil is disturbed, the more likely seeds will emerge and sprout. That’s why these plants are so invasive in areas with poor to average soil disturbed by logging, fire, and storms.
Drought-tolerant and prolific seed producers (a whopping 100,000‑240,000 seeds per plant), the plant grows quite easily from seed. Here’s how:
- Start seeds indoors in early spring or outdoors in late spring.
- Scatter them on the top of rich potting soil or sow a pinch of seeds 18 inches apart and just 1/16 inch deep in well-drained soil. Look for sprouts two weeks later.
- Once indoor plants have grown a true set of leaves, divide and transplant the seedlings into a bigger container or harden them off and transplant them into the garden. For plants seeded directly in the garden, thin seedlings to at least 12 inches apart.
- Because these plants readily self-sow, remove unwanted plants to keep your garden from being overrun with mullein.
Pests and Diseases
Mullein is resistant to pests. Aphids are only rarely a problem. Avoid planting mullein in heavily compacted soil as such poorly draining soil can encourage root rot.
Overwintering
Mullein is winter hardy but for extra root protection, mulch before the projected frost date with twigs, leaves, and bark.
III. Uses and Benefits
- Phytochemicals
Phytochemicals in V. thapsus flowers and leaves include saponins, polysaccharides, mucilage, flavonoids, tannins, iridoid and lignin glycosides, and essential oils. The plant’s leaves, in addition to the seeds, have been reported to contain rotenone, although quantities are unknown.
- Traditional medicine
Although long used in herbal medicine, no drugs are manufactured from its components. Dioscorides first recommended the plant 2000 years ago, considering it useful as a folk medicine for pulmonary diseases. Leaves were smoked to attempt to treat lung ailments, a tradition that in America was rapidly transmitted to Native American peoples. The Zuni people, however, use the plant in poultices of powdered root applied to sores, rashes, and skin infections. An infusion of the root is also used to treat an athlete’s foot. All preparations meant to be drunk have to be finely filtered to eliminate the irritating hairs.
Oil from the flowers was used against catarrhs, colics, earaches, frostbite, eczema, and other external conditions. Topical application of various V. thapsus-based preparations was recommended for the treatment of warts, boils, carbuncles, hemorrhoids, and chilblains, amongst others. Glycyrrhizin compounds with bactericide effects in vitro were isolated from flowers. The German Commission E describes uses of the plant for respiratory infections. It was also part of the National Formulary in the United States and United Kingdom.
The plant has been used in an attempt to treat colds, croup, sunburn, and other skin irritations.
- Other uses
Roman soldiers are said to have dipped the plant stalks in grease for use as torches. Other cultures use the leaves as wicks. Native Americans and American colonists lined their shoes with leaves from the plant to keep out the cold.
Mullein may be cultivated as an ornamental plant. As for many plants, (Pliny the Elder described it in his Naturalis Historia), great mullein was linked to witches, although the relationship remained generally ambiguous, and the plant was also widely held to ward off curses and evil spirits. The seeds contain several compounds (saponins, glycosides, coumarin, rotenone) that are toxic to fish, and have been widely used as piscicide for fishing.
Due to its weedy capacities, the plant, unlike other species of the genus (such as V. phoeniceum), is not often cultivated.