Soil & potting mix
Best soil for 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.
Preferred mix: Lean, alkaline to neutral, sharply drained soil or wall crevice
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.
Why rock cress needs this mix
Rock Cress is a Mediterranean dry-hillside plant — it wants a lean, sharply drained, slightly alkaline mix, and rots fast in rich, water-holding soil.
- Rock Cress evolved on stony, sun-baked slopes — its roots expect to dry out hard and quickly between rains, so the mix must drain almost as fast as you pour.
- A lean, low-nutrient mix keeps growth firm and aromatic; a rich one gives soft, sappy, flavourless growth that flops and rots.
- It tolerates and often prefers a slightly alkaline soil, the opposite of most houseplants.
For the full picture on what makes up a good mix, see our guide to the main types of soil and potting media — it explains why each ingredient above behaves the way it does.
What goes wrong with the wrong mix
The wrong soil is one of the most common reasons rock cress struggles, and the damage often shows up weeks later as a watering problem. For this species specifically:
- Rich, moisture-holding compost is the classic killer of rock cress — especially over a cold, wet winter, when the base of the plant simply rots.
- A peaty, acidic potting mix is doubly wrong: too wet and the wrong pH direction.
- No grit means the rootball stays damp for days, which a dry-climate root system never copes with.
Growing rock cress in ordinary rich, moisture-retentive compost. Lean it out with at least a third grit, and never let it sit wet over winter.
pH — does it matter for rock cress?
Rock Cress likes neutral to slightly alkaline soil, roughly pH 6.5-7.5. If your soil or compost is acidic, a little garden lime or extra grit nudges it the right way — the one common plant where you may add lime.
If you want to check or adjust it, the soil pH guide walks through testing and the safe ways to nudge a mix more acidic or more alkaline.
DIY mix vs a bagged one
Bagged "herb" or "Mediterranean" mixes are usually fine for rock cress, but most standard composts need cutting hard with grit. The DIY ratio above is cheap and exactly right.
Drainage and the pot
Sharp drainage is everything: a terracotta pot with a big hole, gritty mix and never a saucer left full. Raised beds suit these herbs outdoors for the same reason.
A gritty mix barely breaks down, so rock cress needs little repotting — refresh the top layer and the grit every couple of years rather than potting on aggressively. When the time comes, our repotting guide for rock cress covers the timing and technique step by step.
Rock Cress soil — frequently asked questions
What is the best soil mix for rock cress?
2 parts standard peat-free compost or loam : 1 part coarse horticultural grit : 1 part perlite or coarse sand. Rock Cress evolved on stony, sun-baked slopes — its roots expect to dry out hard and quickly between rains, so the mix must drain almost as fast as you pour.
Can I use normal potting soil for rock cress?
Rich, moisture-holding compost is the classic killer of rock cress — especially over a cold, wet winter, when the base of the plant simply rots. Bagged "herb" or "Mediterranean" mixes are usually fine for rock cress, but most standard composts need cutting hard with grit. The DIY ratio above is cheap and exactly right.
Does rock cress need a special pH?
Rock Cress likes neutral to slightly alkaline soil, roughly pH 6.5-7.5. If your soil or compost is acidic, a little garden lime or extra grit nudges it the right way — the one common plant where you may add lime.
Should I buy a bagged mix or make my own for rock cress?
Bagged "herb" or "Mediterranean" mixes are usually fine for rock cress, but most standard composts need cutting hard with grit. The DIY ratio above is cheap and exactly right.
How often should I refresh the soil for rock cress?
A gritty mix barely breaks down, so rock cress needs little repotting — refresh the top layer and the grit every couple of years rather than potting on aggressively. Sharp drainage is everything: a terracotta pot with a big hole, gritty mix and never a saucer left full. Raised beds suit these herbs outdoors for the same reason.
Keep reading
- Rock Cress care — the full brief (light, water, humidity, problems, pet safety)
- How often to water rock cress — the schedule the mix feeds into
- Repotting rock cress — when and how to refresh the mix
- Soil pH guide — test it and adjust it safely
- Overwatered plant — signs and recovery
- Root rot — how the wrong soil starts it, and how to save the plant
- Should I water my plant? The simple check first
- Best soil for chinese witch hazel
- Best soil for jelena witch hazel
- Best soil for mountain laurel
- All 8452 soil and potting-mix guides in the Growli library