Mature size & growth rate

How big does Common Mullein (Verbascum thapsus) get?

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

More about common mullein

About Common Mullein

Verbascum thapsus · also called Common Mullein, Great Mullein · herb

Common Mullein is a stately biennial forming a basal rosette of large, densely woolly grey-green leaves in year one, then sending up a towering flower spike to 2 m covered in yellow flowers in year two. Historically used in herbal medicine for respiratory complaints, it thrives in poor, dry, disturbed soils and full sun. Excellent for wildlife gardens.

Mature size: Up to 2 m tall in flower; rosette to 60 cm across

Indoor size vs how big it gets in the wild

Common Mullein reaches its full size within one growing season — there is no "long-term" size, just how big it gets before you harvest or it dies back. Indoors and in a pot, expect up to 2 m tall in flower. In the ground with no restriction it is a completely different plant — rosette to 60 cm across — which is why the pot, the light and the pruning matter so much for the size you actually end up with.

It sizes up fast and once, racing from seedling to full size in a single season; after cropping it is finished, so size is a within-season question.

Growth rate and years to mature

Common Mullein is a moderate grower. Realistically, expect a single growing season — it reaches full size in one year, then is done. Its feeding profile backs this up: no fertilising needed or recommended. adding fertiliser encourages lush, soft growth more prone to disease and reduces the plant's architectural quality. in extremely impoverished soils, a single application of balanced slow-release granules at planting supports establishment of the year-one rosette.

Want this turned into the right next pot at the right moment? The pot size calculator and the common mullein repotting guide cover when and how much to size up — pot size is one of the biggest levers on how fast common mullein grows.

How to keep common mullein smaller

You are not stuck with the maximum size. For common mullein specifically, these are the levers, in order of impact:

Choose a compact or dwarf variety of common mullein from the start — that is the most reliable size control for an annual.
Grow it in a smaller container to naturally limit how large it gets.
For some crops, pinching or pruning the growing tips keeps the plant shorter and bushier.
Sow a little later or space plants closer if you specifically want smaller individual plants.

How to grow common mullein bigger or faster

If you want it to fill the space sooner, push the conditions rather than hoping — for common mullein the accelerators are:

Full sun, warm soil and steady water are what drive a crop to full size fastest.
Sow at the right time for your zone so it gets the whole season to size up.
Feed appropriately for the crop and never let it check (stall) from drought or cold.

Light is almost always the ceiling. The common mullein light requirements page covers exactly how bright a spot it needs to grow at its potential instead of stalling.

When common mullein outgrows the room (or the pot)

"Too big" usually arrives as one of these signs for common mullein:

It sprawls beyond its bed or container before harvest — usually a spacing or support issue.
It flops or needs staking once it hits full height.
Once it has fruited or bolted, it is at its final size for good — the next plant is a new sowing.

If it is the pot rather than the room, it is a repotting job, not a goodbye — see the common mullein repotting guide. If you want more of this plant instead of a bigger one, the common mullein propagation guide turns prunings into new plants.

Common Mullein size — frequently asked questions

How big does common mullein get?

Common Mullein reaches up to 2 m tall in flower when grown indoors, and far larger where it grows unrestricted (rosette to 60 cm across). It sizes up fast and once, racing from seedling to full size in a single season; after cropping it is finished, so size is a within-season question.

Is common mullein slow or fast growing?

Common Mullein is a moderate grower. Expect a single growing season — it reaches full size in one year, then is done. Common Mullein reaches its full size within one growing season — there is no "long-term" size, just how big it gets before you harvest or it dies back.

How long does common mullein take to reach full size?

Roughly a single growing season — it reaches full size in one year, then is done. Light, pot size and feeding move that timeline more than anything else.

How do I keep common mullein smaller?

Choose a compact or dwarf variety of common mullein from the start — that is the most reliable size control for an annual. Grow it in a smaller container to naturally limit how large it gets. For some crops, pinching or pruning the growing tips keeps the plant shorter and bushier. Sow a little later or space plants closer if you specifically want smaller individual plants.

How can I make common mullein grow bigger or faster?

Full sun, warm soil and steady water are what drive a crop to full size fastest. Sow at the right time for your zone so it gets the whole season to size up. Feed appropriately for the crop and never let it check (stall) from drought or cold.