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Plant care

Great Mullein (Common Mullein) care

Verbascum thapsus

Also called Great Mullein, Common Mullein, Aaron's Rod, Flannel Plant.

RHS H6USDA 3-9Mildly toxic to petsIndoor Rosette to 60 cm across in year one

Watering rhythm

Direct sun (at least 4-6 hours)

Low — once established, rainfall is usually sufficient

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Light

Direct sun (at least 4-6 hours)

Soil

Sandy or loamy, well-drained, low fertility

Humidity

Low to moderate

Temp

-30 to 35°C

Pet safety

Mildly toxic to pets

Mature size

Rosette to 60 cm across in year one

Care at a glance

Light

Most houseplants will scorch where great mullein thrives. Give it the windowsill you'd otherwise leave empty because everything else burned there. Requires full sun for at least 6 hours a day; plants that receive too much shade produce weak, floppy flower spikes and are more susceptible to fungal issues. A plant moved abruptly from low light to direct sun bleaches in 48 hours — always acclimatise over a week.

Watering

Aim for low — once established, rainfall is usually sufficient for great mullein, but treat that as a starting point rather than a rule. A south-facing summer windowsill will dry the pot twice as fast as a north-facing winter room. Lift the pot; if it feels noticeably lighter than it did wet, water it. Drought-tolerant once the taproot is established; water seedlings regularly until settled but avoid standing water around the crown, which causes rot.

Soil and pot

Great Mullein grows best in sandy or loamy, well-drained, low fertility. Thrives in infertile, alkaline to neutral soils; rich, moist soil encourages soft growth and weakens the plant's natural resilience. A pot with a working drainage hole is non-negotiable for this species — even free-draining mix will turn soggy in a closed planter. If you love the look of a decorative pot without a hole, use it as a cachepot around an inner nursery pot you can lift out to water.

Humidity and temperature

Great Mullein sits happiest at around Low to moderate humidity and -30 to 35°C (-22 to 95°F). Tolerates dry air well; dense leaf hairs are an adaptation to arid conditions, and persistently humid conditions increase powdery mildew risk. If you keep the room above year-round and avoid placing the plant near a cold draught, a hot radiator, or an air-conditioning vent, you have already handled the two biggest indoor stressors.

Fertilising

Feed great mullein sparingly. Fertilising is unnecessary and counterproductive — great mullein performs best in poor soils without supplemental feeding. Skip fertiliser entirely on a stressed, recently-repotted, or actively wilting plant — fertiliser salts make damage worse, not better. Wait for a round of healthy new growth before resuming a feeding rhythm.

Common problems

Below are the issues we see most often on great mullein in the Growli community. Each is annotated with the most common cause so you know where to start.

  • Mullein moth caterpillars (Cucullia verbasci) — Yellow, black, and white spotted caterpillars can skeletonise leaves rapidly; hand-pick caterpillars promptly as they are rarely numerous enough to warrant chemical control.
  • Crown rot in wet soils — The woolly crown rots quickly in waterlogged or poorly drained ground; always plant in an open, sunny position with free-draining soil and avoid overhead watering.

Propagation

Sow seed on the surface of gritty compost in autumn or spring (needs light to germinate); self-seeds prolifically once established and naturalises readily. Propagation is the cheapest, most satisfying way to expand a collection — and it doubles as insurance against losing a mature plant to an accident. Take a backup cutting once the parent is established and healthy.

Toxicity to pets

Great Mullein is mildly toxic to pets. Verbascum thapsus is not listed on the ASPCA toxic plant database. However, the dense, stiff hairs on leaves and stems can cause contact irritation or mechanical irritation of the mouth and gastrointestinal tract in cats and dogs if ingested in quantity, so 'mildly-toxic' is the prudent classification. If you keep cats, dogs, or curious children in the house, weigh placement carefully — a high shelf or a hanging planter is enough for casual safety. For severe ingestion incidents, call your local vet and the ASPCA Animal Poison Control Center (in the US, 888-426-4435).

Pet-safety status is sourced from the ASPCA Toxic and Non-Toxic Plant List, which catalogues the most-asked-about plants for cats, dogs, and horses.

Great Mullein care — frequently asked questions

What is the common name for Verbascum thapsus?

Verbascum thapsus is most commonly called Great Mullein, but it is also known as Great Mullein, Common Mullein, Aaron's Rod, Flannel Plant. The names refer to the same species, so care instructions for Great Mullein apply identically to anything sold as Common Mullein.

How much light does great mullein need?

Great Mullein grows best in direct sun (at least 4-6 hours). Requires full sun for at least 6 hours a day; plants that receive too much shade produce weak, floppy flower spikes and are more susceptible to fungal issues.

How often should I water great mullein?

Water great mullein low — once established, rainfall is usually sufficient. Drought-tolerant once the taproot is established; water seedlings regularly until settled but avoid standing water around the crown, which causes rot. The finger-test (or lifting the pot to feel its weight) beats a fixed weekly calendar because pot size, light, and season all change how fast the soil dries.

Is great mullein toxic to cats and dogs?

Great Mullein is mildly toxic to pets. Verbascum thapsus is not listed on the ASPCA toxic plant database. However, the dense, stiff hairs on leaves and stems can cause contact irritation or mechanical irritation of the mouth and gastrointestinal tract in cats and dogs if ingested in quantity, so 'mildly-toxic' is the prudent classification.

What USDA hardiness zone does great mullein grow in?

Great Mullein is rated for USDA zone 3-9 and RHS hardiness H6. Outside that range, grow it as a container plant that overwinters indoors before the first hard frost.

Great Mullein deep-dive guides

Every aspect of great mullein care, each with its own calibrated guide:

Featured in these plant shortlists

Great Mullein qualifies for 4 curated Growli shortlists — each one filtered objectively from our structured plant-care library, so the selection is consistent and checkable:

Related guides

Great Mullein is also known as Great Mullein, Common Mullein, Aaron's Rod, and Flannel Plant.