How to Grow Verbascum UK – Mullein for Sunny, Dry Borders

Verbascum – mullein – is one of the most dramatically architectural plants available for a sunny, dry UK garden border. The large-leaved basal rosettes of the bigger species are impressive in their own right through winter and spring, but it is the flower spikes that make verbascum unmistakeable: vertical columns rising to 150-200cm in the tallest species, densely studded with yellow, white, pink or purple flowers that open progressively from the base upward through June, July and August. The silver-grey woolly coating on the leaves and stems of species such as V. bombyciferum catches low sunlight and creates a luminous, almost glowing effect that few other garden plants replicate. As a single specimen plant in a gravel garden or as a bold vertical accent at the back of a sunny border, a large verbascum commands attention in a way that no perennial of similar cultural requirements can match.

The genus spans a wide range from the towering biennials native to Mediterranean hillsides and central Asian steppes to compact perennial hybrids bred for smaller UK gardens. Understanding whether a particular verbascum is biennial or perennial changes how it is managed entirely – biennials flower magnificently in their second year and then die, while perennial hybrids return reliably each year and slowly build into larger clumps. Many verbascum cultivars available in UK garden centres are short-lived perennials that behave somewhere between the two – flowering in their first summer if planted early enough, persisting for two or three years, and then declining. Knowing which type you are growing helps set realistic expectations and determines whether you need to manage self-seeding to maintain the colony.

Growing Conditions

Verbascum requires exactly the conditions that most gardeners struggle to provide for other ornamentals: full sun, poor soil and excellent drainage. Rich, fertile, moist soil causes the plants to produce excessive leafy growth at the expense of the flower spikes, and the crowns become vulnerable to rotting in wet winter conditions. The silver woolly coating on the leaves of species like V. bombyciferum is an adaptation to intense summer heat and low rainfall – it reflects light, reduces water loss and insulates the leaf surface. In a UK garden, replicating these conditions as closely as possible – a south-facing position, gritty soil, minimal watering and no feeding – produces plants that perform as impressively as they do on their native rocky slopes. Add generous compost and regular watering and you get a floppy, rot-prone disappointment instead.

Drainage is the critical factor over winter. Verbascum leaves and stems accumulate moisture in the felt-like coating on their surfaces, and if this stays wet for extended periods in cold conditions the crown can rot. On free-draining sandy or chalky soils verbascum overwinters reliably across the UK. On clay soils, raise the planting area with grit or plant into a slightly elevated position where water runs away rather than pooling. The plants that fail in UK gardens almost always do so in winter on heavy, wet soils – the same plants in the same garden but positioned on a free-draining raised bed or slope survive indefinitely.

Best Varieties for UK Gardens

V. bombyciferum is the showstopper of the genus – a massive biennial with enormous basal rosettes of silver-woolly leaves up to 40cm across, and flower spikes that reach 180-200cm in good conditions. The entire plant is coated in a dense, white felt that gives it a luminous quality unlike any other garden plant. It is striking enough to be used as a specimen plant in its own right rather than just a border filler, and in a gravel garden setting where the silver foliage contrasts with the grey stone it is genuinely memorable. V. phoeniceum opens the colour range – its slender spikes of purple, pink and white flowers are more delicate than the heavy yellow spikes of the taller species and suit naturalistic or cottage-garden style planting alongside salvias and grasses.

Planting and Propagation

Container-grown verbascum can be planted from spring through to early autumn. Spring planting is ideal for biennial species – a plant put in during April or May builds a strong rosette through the summer and flowers reliably the following June. For short-lived perennial hybrids, spring planting often produces flowers in the first summer if conditions are warm enough, though the first-year display is typically less substantial than in subsequent seasons. Plant into well-drained soil with generous grit incorporated if the ground is at all heavy, and position at the back or middle of a sunny border where the eventual height can be accommodated without blocking smaller plants.

Propagation from seed is straightforward and produces flowering plants more reliably than any other method for the species forms. Sow V. bombyciferum and V. phoeniceum in modules or seed trays in May or June, germinate on a warm windowsill or in a cold frame, and grow on until large enough to plant out in autumn. Biennial seedlings sown in summer will have built substantial rosettes by autumn and flower strongly the following June. Root cuttings taken in autumn or winter are the correct method for propagating named hybrid cultivars – the hybrids do not come true from seed and root cuttings are the only reliable way to maintain a specific variety. Take root sections 5-8cm long from vigorous plants in autumn, insert vertically in a gritty compost mix and keep frost-free until spring shoots emerge.

Care, Cutting Back and Common Problems

Established verbascum is one of the lowest-maintenance plants in a dry, sunny border. No feeding, minimal watering, no staking needed in an open position – the main annual task is removing the spent flower spikes and any dead basal foliage. Cutting the central spike to the ground after flowering can stimulate branched side shoots that carry smaller secondary flowers, extending the display by several weeks. Whether to do this or leave the spike to set seed depends on whether you want to encourage self-seeding to maintain the colony – biennial species require some self-seeding to persist in the garden, while perennial hybrids that are maintained by root cuttings can be deadheaded without concern. The dried seed heads of the taller species also have genuine ornamental value through autumn and early winter, when the stiff brown columns catch frost and hold their structure through mild UK weather before finally collapsing in heavy rain or sustained frost.