Mullein (genus Verbascum) includes biennials, such as the common mullein (Verbascum thapsus), and true perennials, popular in ornamental and medicinal gardens alike. Mullein’s deep taproot allows it to thrive in conditions where many other plants struggle. To increase your population of this hardy plant, two primary methods are employed: sowing seeds and propagating via root cuttings.
Optimal Environment and Timing
Mullein thrives in dry, sunny environments and requires full sun exposure. Its deep taproot makes it highly tolerant of poor, sandy, or rocky soils, preferring well-drained conditions over rich, heavy ones. Overly fertile soil or excessive moisture can lead to root issues, so lean conditions are more suitable for robust growth.
For seed starting, late fall or early spring are the best seasons for sowing directly outdoors. Sowing in the fall allows the seeds to undergo natural cold stratification over the winter, which is required for breaking dormancy. Root cuttings should be timed when the plant is dormant, typically during late fall after the foliage dies back or in early spring before new growth begins.
Step-by-Step Seed Propagation
Seed propagation is the most common way to grow mullein. The seeds require light for successful germination, so they must not be buried deeply beneath the soil surface. After collecting seeds from dried, mature seed pods, scatter them lightly over prepared, well-draining soil and gently press them down.
To ensure germination, cold stratification is often necessary. This involves mixing the seeds with a slightly moistened medium, such as sand or vermiculite, placing them in a sealed container, and refrigerating them at temperatures between 33 and 38°F for approximately 30 days. The seeds can then be sown indoors six to eight weeks before the last expected frost or directly into the garden.
The seeds should be kept consistently moist until they sprout, which can take between 14 and 20 days. When starting indoors, use shallow seed trays with a fine-grained, well-draining soil mix and avoid covering the seeds with more than a light dusting of soil. Once the seedlings have developed at least two sets of true leaves, they can be carefully transplanted to their final outdoor location, taking care not to disturb the developing taproot.
Propagation Using Root Cuttings
Root cuttings offer an alternative propagation method, useful for perennial mullein species or when cloning a desirable parent plant is the goal. Begin by carefully excavating a healthy parent plant during its dormant phase to access the root system.
Select a section of the thick, fleshy taproot and use a sharp, sterilized knife to excise small pieces, approximately one to two inches in length. Some gardeners mark the orientation by making a straight cut at the root crown end and a slanted cut at the lower end. These root sections are then laid horizontally or planted vertically, with the crown end facing up, into a tray filled with a moist, sandy potting mix.
The cuttings should be covered with a thin layer of soil, about a quarter to a half-inch deep, and kept in a cool location with consistent moisture. Within a few weeks, the root segments will begin to form new shoots and roots. Once a strong rosette of leaves appears, the new plants can be hardened off and transplanted into the garden.