Repotting guide

When & how to repot Rock Cress (Aubrieta deltoidea)

Also called Rock Cress, Aubrieta, Purple Rock Cress.

More about rock cress

About Rock Cress

Aubrieta deltoidea · also called Rock Cress, Aubrieta · flowering

A vigorous, mat-forming perennial producing masses of small cross-shaped flowers in shades of purple, lilac, mauve, and pink in spring. Native to stony habitats from south-eastern Europe to western Asia. Widely grown to cascade over walls, rock gardens, and raised beds. Thrives in poor, alkaline soils with full sun and sharp drainage.

Mature size: 10–15 cm tall, spreading to 60–90 cm wide

Watch for — Straggly, open growth after flowering: Plants become untidy and bare at the centre if not cut back after flowering. Trim back hard by about two-thirds immediately after flowering in late spring to encourage compact, fresh growth and a second flush of blooms.

How to tell rock cress needs repotting

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

Roots spiralling thickly out of the drainage holes or pushing the whole plant up out of the pot.
The pot is so packed that water runs straight through in seconds and barely wets the soil.
It has split a plastic pot, or the rootball is a solid mass with almost no soil left when you slide it out.
Growth and (for rock cress) flowering have clearly stalled despite good light and feeding — but remember this plant likes being snug, so a little crowding alone is not a reason to 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 rock cress

Only every 2–4 years, when genuinely crowded. Rock Cress is one of the plants that genuinely prefers a snug pot — it grows and flowers better with its roots a little restricted, so resist the urge to repot it on schedule. Spreading, mat-forming perennial; semi-evergreen with small, slightly hairy grey-green leaves.

What size pot to step rock cress up to

Go up only one pot size — roughly 2–3 cm (about an inch) wider in diameter, no more. Rock Cress positively prefers a snug pot: it flowers and grows better when the roots are a little restricted. The single biggest repotting mistake here is over-potting — dropping rock cress into a pot two or three sizes up. All that surplus soil holds water the small root system cannot use, stays cold and wet, and rots the roots within weeks. When in doubt, choose the smaller pot.

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 rock cress

Early spring, just as new growth restarts, is the ideal window for rock cress. 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 rock cress

Confirm it actually needs it. Slide rock cress out and check the roots. Only continue if it is genuinely packed — this plant prefers a snug pot, so if there is still soil and room, put it straight back.
Pick a pot only one size up. Choose a pot just 2–3 cm wider with good drainage. Resist anything bigger; over-potting is the main killer here.
Ease it out gently. Water lightly the day before, then tip rock cress out, supporting the base. Tease the outer roots free only enough to stop them circling.
Repot at the same depth. Add a layer of fresh lean, alkaline to neutral, sharply drained soil or wall crevice, set the plant so the soil line sits exactly where it did before, and backfill around the sides, firming lightly.
Settle it in. Water once to settle the soil, then let it sit. Hold off on more water until the top of the soil dries — fresh soil around a small root system stays wet for a while.

Aftercare

Because the new soil holds more water than the old crammed rootball did, ease right back on watering — let the top of the soil dry before you water rock cress again, or you will rot the roots in the very pot you just moved it to. Keep it out of harsh direct sun for a fortnight. Do not fertilise for about 4 weeks — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.

The right soil mix for rock cress

Rock Cress wants lean, alkaline to neutral, sharply drained soil or wall crevice. pH 6.5–8.0. Thrives in poor, stony or chalky soils. Add coarse grit to heavier garden soils to improve drainage. Actively prefers alkaline conditions — add limestone grit if soil is acidic. Rich, fertile soils produce excessive leafy growth at the expense of flowers. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting rock cress — frequently asked questions

How often should you repot rock cress?

Only every 2–4 years, when genuinely crowded for rock cress. Only repot rock cress every 2–4 years, and only when it is genuinely root-bound — it flowers and grows best slightly crowded. Step up just one pot size in spring using lean, alkaline to neutral, sharply drained soil or wall crevice. The key mistake is over-potting: a too-big pot stays wet and rots the roots.

What size pot does rock cress need?

When is the best time of year to repot rock cress?

Does rock cress like to be root-bound?

Yes — rock cress genuinely flowers and grows best when slightly pot-bound, so do not rush to repot it. The mistake to avoid is over-potting into a much larger pot: the excess soil stays wet, the roots cannot use it, and the plant rots. Only repot every few years and only one snug size up.

Should you fertilise rock cress after repotting?

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