Repotting guide

When & how to repot Hairy Rock-cress (Arabis hirsuta)

Also called Hairy Rock-cress, Hairy Rockcress, Mountain Rockcress.

More about hairy rock-cress

About Hairy Rock-cress

Arabis hirsuta · also called Hairy Rock-cress, Hairy Rockcress · flowering

Arabis hirsuta is a small biennial or short-lived perennial in the Brassicaceae family, native to calcareous grasslands, rocky outcrops, walls, and limestone pavements across Europe and North America. It forms a rosette of hairy, oblong leaves from which erect flowering stems carry small four-petalled white flowers from May to August. The most important care fact is that it is strictly a calcicole — it grows on base-rich, well-drained, alkaline or neutral substrates and will not persist on acid soils. No significant toxicity to pets has been reported.

Mature size: 10–60 cm tall; basal rosette 10–20 cm across.

How to tell hairy rock-cress needs repotting

Repotting on a calendar is less reliable than reading the plant. For hairy 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 hairy 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 hairy rock-cress

Only every 2–4 years, when genuinely crowded. Hairy 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. Erect biennial or short-lived perennial forming a basal rosette in the first year; unbranched or slightly branched stems rise to 60 cm in the second year carrying the flower raceme..

What size pot to step hairy rock-cress up to

Go up only one pot size — roughly 2–3 cm (about an inch) wider in diameter, no more. Hairy 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 hairy 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 hairy rock-cress

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

Confirm it actually needs it. Slide hairy 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 hairy 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 well-drained, calcareous, low-fertility, 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 hairy 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 hairy rock-cress

Hairy Rock-cress wants well-drained, calcareous, low-fertility. Demands an alkaline to neutral pH and sharp drainage; typical habitats are chalk or limestone rubble, dry stone walls, and scree. Avoid enriched or compacted soils. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting hairy rock-cress — frequently asked questions

How often should you repot hairy rock-cress?

Only every 2–4 years, when genuinely crowded for hairy rock-cress. Only repot hairy 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 well-drained, calcareous, low-fertility. The key mistake is over-potting: a too-big pot stays wet and rots the roots.

What size pot does hairy rock-cress need?

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

Does hairy rock-cress like to be root-bound?

Yes — hairy 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 hairy rock-cress after repotting?

Not immediately. Wait about 4 weeks after repotting hairy 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.