Mature size & growth rate

How big does Olympic Mullein (Verbascum olympicum) get?

Also called Olympic Mullein, Greek Mullein, Branching Mullein.

More about olympic mullein

About Olympic Mullein

Verbascum olympicum · also called Olympic Mullein, Greek Mullein · flowering

Olympic Mullein is a dramatic, architectural biennial or short-lived perennial from Greece and Turkey, producing a massive basal rosette of silver-white woolly leaves followed by a candelabra-branched flower spike reaching 1.8–2.5 m and studded with golden-yellow blooms. Spectacular as a focal point in dry, sunny borders, gravel gardens, and Mediterranean-style planting schemes.

Mature size: 1.8–2.5 m tall in flower; rosette up to 90 cm across

Indoor size vs how big it gets in the wild

Olympic 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 1.8–2.5 m tall in flower. In the ground with no restriction it is a completely different plant — rosette up to 90 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

Olympic 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 feeding required in poor soils; this is the preferred condition. in moderately fertile garden soil, a light dressing of slow-release balanced fertiliser in spring of year two supports flower spike development. over-feeding produces fast, weak growth and reduces the striking silver colouring of the leaf rosette.

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

How to keep olympic mullein smaller

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

Choose a compact or dwarf variety of olympic 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 olympic mullein bigger or faster

If you want it to fill the space sooner, push the conditions rather than hoping — for olympic 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 olympic mullein light requirements page covers exactly how bright a spot it needs to grow at its potential instead of stalling.

When olympic mullein outgrows the room (or the pot)

"Too big" usually arrives as one of these signs for olympic 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 olympic mullein repotting guide. If you want more of this plant instead of a bigger one, the olympic mullein propagation guide turns prunings into new plants.

Olympic Mullein size — frequently asked questions

How big does olympic mullein get?

Olympic Mullein reaches 1.8–2.5 m tall in flower when grown indoors, and far larger where it grows unrestricted (rosette up to 90 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 olympic mullein slow or fast growing?

Olympic Mullein is a moderate grower. Expect a single growing season — it reaches full size in one year, then is done. Olympic 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 olympic 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 olympic mullein smaller?

Choose a compact or dwarf variety of olympic 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 olympic 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.