Repotting guide

When & how to repot Stock (Matthiola incana)

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.

How to tell stock needs repotting

Repotting on a calendar is less reliable than reading the plant. For stock, watch for these signs:

Thick roots out of the drainage holes, or circling the surface and lifting the plant.
The pot dries out unusually fast and stock wilts between waterings it used to shrug off.
The plant is visibly top-heavy and tips over easily.
Stalled growth and small new leaves over a full season — though with a big specimen, top-dressing is often the better first response before a full repot.

For the underlying biology of a pot-bound root system and why it stalls a plant, see our guide to spotting and fixing a root-bound plant.

How often to repot stock

Every 2–3 years; top-dress in the in-between years. Stock's growth habit — erect, woody-based biennial or short-lived perennial; branched stems with grey-green woolly leaves and dense terminal flower racemes — sets the pace. 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.

What size pot to step stock up to

Move up exactly one pot size. A heavy stock dropped into a vastly bigger pot sits in a reservoir of wet soil its roots cannot reach, which rots them and destabilises the plant. In the years between repots, lift off and replace the top 3–5 cm of soil (top-dressing) instead — it refreshes nutrients without the shock of a full repot.

Not sure of the exact diameter? Our pot size calculator takes the current pot and root spread and tells you the right next size — it deliberately recommends a single step up, never a big jump.

The best time of year to repot stock

Early spring, just as new growth restarts, is the ideal window for stock. The plant is moving into its strongest growth phase and re-roots into fresh soil quickly. Avoid repotting in winter dormancy or, for flowering plants, while it is in bud or bloom — recovery is slowest then and you risk dropping the flowers.

Step-by-step: repotting stock

Consider top-dressing first. If stock is not badly root-bound, scrape off and replace the top 3–5 cm of soil instead — far less shock for a big plant that hates moving.
Get help and one size up. For a full repot, choose a pot just one size larger. A heavy plant needs two people and a stable, free-draining pot.
Ease it out on its side. Lay the plant down, slide the pot off, and gently loosen the outer roots. Do not bare-root a mature specimen.
Repot at the same depth. Add fresh well-drained, moderately fertile loam, chalk, or sandy loam, ph 6.5–7.5 beneath and around the rootball, keeping the original soil line. Firm it so the trunk is stable and upright.
Water and leave it put. Water thoroughly, then leave stock in the same spot and light — moving and repotting at once is what makes it drop leaves.

Aftercare

Leave stock in exactly the same spot and light it was in before — moving and repotting at the same time is what makes a big specimen drop leaves. Water it in well, then let the top of the soil dry before watering again so the larger volume of fresh soil does not stay sodden. Do not fertilise for about 4 weeks — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.

The right soil mix for stock

Stock wants well-drained, moderately fertile loam, chalk, or sandy loam, ph 6.5–7.5. Matthiola incana prefers neutral to mildly alkaline, well-drained soils enriched with compost. It performs poorly in acidic soils. Lime heavy soils before planting if pH is below 6.5. Good drainage is essential as it cannot tolerate wet feet. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting stock — frequently asked questions

How often should you repot stock?

Every 2–3 years; top-dress in the in-between years for stock. Fully repot stock only every 2–3 years; in the in-between years just top-dress the top 3–5 cm of soil. Step up one pot size in spring with well-drained, moderately fertile loam, chalk, or sandy loam, ph 6.5–7.5. It is heavy and hates being moved, and a vastly oversized pot holds water against the roots and rots them.

What size pot does stock need?

When is the best time of year to repot stock?

Should you top-dress or fully repot stock?

For a big, heavy stock, top-dressing — replacing the top 3–5 cm of soil — is the gentler option most years, with a full repot only every 2–3 years. A mature specimen sulks and drops leaves when fully repotted, so do it as rarely as the roots allow.

Should you fertilise stock after repotting?

Not immediately. Wait about 4 weeks after repotting stock. Fresh mix already contains nutrients, and feeding freshly cut or disturbed roots burns them. Resume your normal feeding routine once you see new growth.