Mature size & growth rate

How big does Stock (Matthiola incana) get?

Also called Stock, Brompton stock, Gillyflower, Ten-week stock, Hoary stock.

More about stock

About Stock

Matthiola incana · also called Stock, Brompton stock · flowering

Stock is a beloved cool-season annual or biennial prized for its intensely clove-scented spikes of flowers in purple, pink, white, and red — a staple of cottage gardens and the floristry trade. It thrives in full sun, well-drained alkaline soil, and cool temperatures. Heat ends flowering quickly, so it performs best in spring and autumn.

Mature size: 30–90 cm tall (12–36 in), 20–40 cm spread (8–16 in) depending on cultivar

Watch for — Club root (Plasmodiophora brassicae): Distorted, swollen roots causing wilting and stunted growth. Matthiola is susceptible as a Brassicaceae member. Improve drainage, lime to raise pH above 7.0, and rotate planting sites annually. No effective chemical cure.

Indoor size vs how big it gets in the wild

Stock 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 30–90 cm tall (12–36 in), 20–40 cm spread (8–16 in) depending on cultivar. A pot, your light levels and a little pruning are what set the final size in a home, far more than the plant's theoretical potential.

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

Stock 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: apply a balanced slow-release fertiliser at planting. feed every 3–4 weeks with a liquid balanced feed during the growing season. avoid high-nitrogen feeds in autumn for overwintering brompton types, which can cause lush growth susceptible to frost damage.

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

How to keep stock smaller

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

Choose a compact or dwarf variety of stock 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 stock bigger or faster

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

When stock outgrows the room (or the pot)

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

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 stock repotting guide. If you want more of this plant instead of a bigger one, the stock propagation guide turns prunings into new plants.

Stock size — frequently asked questions

How big does stock get?

Stock reaches 30–90 cm tall (12–36 in), 20–40 cm spread (8–16 in) depending on cultivar when grown indoors. 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 stock slow or fast growing?

Stock is a moderate grower. Expect a single growing season — it reaches full size in one year, then is done. Stock 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 stock 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 stock smaller?

Choose a compact or dwarf variety of stock 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 stock 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.