Verbascum: how to grow verbascum

By Daisy Bowie-Sell

Published: Monday, 23 May 2022 at 12:00 am

What is Verbascum

Verbascum is a varied group of biennials, long-lived perennials and short-lived perennials producing insect-friendly spikes of flowers. Two hundred and fifty species are mostly native to Europe and Turkey, all found on poorer, disturbed soil. They are members of the Scrophulariaceae family.

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When do Verbascum flower?

Verbascum flower between May and September and grow to heights that range from 30cm to 2m or more. An upright habit, although some rosettes can be up to 90 cm wide. All verbascums enjoy a sunny, open site with good drainage – excellent for drier gardens. Many have deep tap roots, allowing them to suck up water in drought conditions.

How to grow Verbascum

Growing verbascums from seed

Verbascum strains and species often set copious amounts of seeds so you may want to remove the seedheads to prevent unwanted seedlings. If you do remove the flowering spikes your plants often live longer. However the winter silhouettes of taller verbascums can be spectacular in the right setting. Commercially available packets of verbascum are easy to find. If saving seeds from the garden, harvest on warm days at midday and cut the seedhead into manageable lengths. Store the seeds somewhere cool and dry.

When to sow Verbascum seeds

Sow in April to May in warm conditions (roughly 15º-18ºC) in trays of seed compost.
Press the seeds into the damp compost.
Move into shade as hot conditions and high temperatures stop germination and halt growth.
Germination will take between 14 and 30 days.
Once the seedlings are large enough to prick out (with two proper leaves) transplant them into 7.5cm pots of John Innes No 1 compost.
Grow on in cool conditions (around 15ºC) until the roots reach the bottom of the pot.
If in doubt, upend carefully and look at the root ball.

Plant them young before the tap root develops. Either plant out into final positions once large enough, watering regularly until the autumn rains come, or plant at the beginning of September. If the strong tap root on a verbascum gets disturbed it fails, so pot-grown plants from a garden centre should be as young as possible. If you do succumb and buy one in full flower, plant it extremely carefully and nurture it well through its first growing season, particularly if it’s been grown in peaty compost.

How to propagate Verbascum

All verbascums can be propagated from root cuttings taken between late autumn and March.
Lift your plant and snip away two or three sections of root close to the crown.
Remove only one-third of the root system or less and replant the original straight away.
Wash the roots and remove any fibrous lateral growth.
Cut each into 5-10cm lengths making a horizontal cut at the upper end and an angled cut at the lower.
The larger surface area of the angled cut helps the plant develop roots and tells you which end is which.
Fill pots with equal parts seed compost and gritty sand or perlite.
Insert each cutting so that the horizontal cut surface is just below the surface, about 6cm apart.
Top dress with 1cm of grit. Water lightly and place in a cold frame. Pot up once true leaves develop: this can take three months or more. Grow on and plant out once large enough. Pests and diseases Mullein moths can eat foliage in summer and they do pupate close to the rosette in winter. Pick them off if they offend you.