How to grow verbascums (mullein)

Val Bourne / 10 March 2015 ( 03 March 2021 )

Find out exactly how to grow tall, striking verbascums (or mullein), such as Verbascum bombyciferum, which can grow up to six feet in height.



Most verbascums (or mullein) are short-lived perennials with saucer-liked flowers that are highly attractive to bees.

Flower spikes like mullein are always good value as they produce masses of flowers without taking up lots of space on the ground and verticals help any border succeed visually as they lead the eye up to the sky and break up the boring hummocky look.

A particularly good variety is Verbascum bombyciferum, also called Broussa or giant mullein, a vertical verbascum that is a summer sorbet of soft-lemon flowers and white swan's down, stretching up into the sky and often reaching over six feet in height. When the bee-friendly flowers fade, before producing their miniscule black seeds, the remaining multi-branched skeleton makes one of the most enduring autumn and winter silhouettes in the garden. Four or five verbascums randomly placed will give great long-term presence.

Where to plant verbascums (mullein)

Verbascum should be planted in well-drained soil and sun.

How to grow verbascums from seed

Some varieties of verbascum are sterile and do not set seeds, while others, such as Verbascum bombyciferum, do.

Non-sterile verbascum such as Verbascum bombyciferum, can be left to self-seed on their own, which they do moderately. Or you can cut the spike and collect the seeds and dry them in the autumn.

If growing verbascum from seed store seeds somewhere cool and dry before planting.

When to sow verbascum seeds

Sow verbascum seeds in mid-spring in seed compost (like John Innes no 1). They should germinate in 14 - 21 days and then the seedlings can be pricked out, once the true leaves appear, into individual three-and-a-half-inch pots.

When to plant out young verbascums

Plant seedlings outside when the roots reach the bottom of the pot, usually in May, and leave the rosette to develop for the first year.

The flower spike will appear in the second year, but the plant will probably only live for 3 - 4 years in well-drained soil.

Alternatively Thompson & Morgan sell seeds labelled ‘Silver Lining’ or you can buy ready-grown plants from Beth Chatto. Other good seed strains include a short purple called ‘Violetta’) and a metre-high white called Verbascum hybridum ‘Snow Maiden’

Propagating sterile verbascums

Some verbascums have sterile flowers which do not set seed and these include the orange-brown ‘Helen Johnson’. These sterile forms have to be propagated from root cuttings taken in early winter, although you will have to dig up the plant. Look for thick, vigorous roots and cut away one or two and then replant the verbascum.

Get a tray of gritty compost and fill almost to the top and cut the root into sections measuring between 1 and 2 cm (half an inch).

Place them bottom down, top up into the compost and leave them to root. By early summer, the root cuttings should have produced some leaves and then these mini plants can be potted up. But patience is sometimes required as they can be slow to get going.

When to cut verbascums back

Most verbascums produce a large rosette and these can get shabby during winter. Tidy well in spring and then leave the plant to perform.

Staking verbascums

The stems are woody and most verbascums, even very tall ones, do not need staking.

Pests

There is a mullein moth which can eat the leaves and the large yellow and blue caterpillars can be a nuisance, although some people choose to plant them as part of a wildlife-friendly garden.

Grow verbascum with…

Having three or four verbascums in a sunny border of silver plants creates long-term presence. You could plant with lavenders, the billowing, later-flowering lavendins form large cloud-like mounds topped with slender long stems of tapering flowers. ‘Seal’ is excellent. Artemisias, anthemis and the herbaceous phlomis, P. russeliana, would also work.

The lemon-yellow flowers and white, downy stems of Verbascum bombyciferum are a fantastic foil for darker blues, purples and magentas - whether its penstemons, dahlias, hardy geraniums or roses.

Visit our plants section for more guides on planting and growing, including more vertical spikes of flowers such as lupins, delphiniums and foxgloves

The opinions expressed are those of the author and are not held by Saga unless specifically stated.

The material is for general information only and does not constitute investment, tax, legal, medical or other form of advice. You should not rely on this information to make (or refrain from making) any decisions. Always obtain independent, professional advice for your own particular situation.