Fertilising guide
How to fertilise Rock Cress (Aubrieta deltoidea)— schedule & NPK
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.
Growth habit: Spreading, mat-forming perennial; semi-evergreen with small, slightly hairy grey-green leaves
Watch for — Short-lived in rich, moist soils: Aubrieta thrives on neglect in lean conditions but declines in fertile, moisture-retentive soils. Improve drainage with grit and avoid feeding heavily. Plants typically live 3–5 years and should be regularly renewed from cuttings.
What fertiliser rock cress actually wants — and why
Rock Cress is an easy, light foliage feeder — a half-strength balanced liquid feed through the growing months keeps it green without forcing weak, sappy growth.
A balanced general houseplant feed (roughly even N-P-K) is exactly right — it is grown for foliage, so steady, moderate nitrogen for healthy leaves is the goal, not a bloom or root formula.
For the language behind the three numbers on the bottle — what nitrogen, phosphorus and potassium each do — see the NPK ratio explained entry. The short version for rock cress: match the feed to the job the plant is doing right now, not to a generic “plant food” on the shelf.
How often to feed rock cress, and which months
Feeding only earns its keep while the plant is in active growth and can use the nutrients — pour feed into a dormant or low-light plant and it simply builds up as root-burning salt. For rock cress:
A light dressing of balanced, slow-release fertiliser in early spring is optional and sufficient. Avoid high-nitrogen feeds which produce excessive leafy growth. Lean soils naturally keep plants compact and floriferous. Treat that as sparingly through the growing season between spring through early autumn (roughly March to September); ease off in autumn and stop entirely in the low light of winter.
The dormant-season rule matters more than the exact interval: skip feeding entirely when rock cress is resting. For the wider context on indoor feeding rhythms across the seasons, the houseplant fertiliser schedule walks through the year month by month.
What strength to mix for rock cress
Half strength is the safe default for rock cress — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
Feeding always goes onto already-damp soil, never dry roots — water rock cress first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the rock cress watering schedule.
Signs you are over-feeding rock cress
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for rock cress:
- Brown, crispy leaf tips and edges with no sign of underwatering.
- A white, crusty salt deposit on the soil surface or pot rim.
- Weak, pale, stretched new growth that flops.
- Lower leaves yellow and drop while the soil is correctly watered.
Signs you are under-feeding rock cress
- Uniformly pale or yellow-green leaves, oldest first.
- Noticeably small new leaves and stalled growth in good light and season.
- A generally tired, lacklustre look despite correct watering and light.
If the symptoms point at watering, light or roots rather than nutrition, the full rock cress care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Flush the pot of rock cress with plain water until it runs freely from the base every couple of months in the feeding season — it washes out the fertiliser salts that cause brown tips.
Organic vs synthetic feeds for rock cress
Organic options
A diluted seaweed or worm-casting feed, or fish emulsion if you can tolerate the smell indoors. UK: Westland or Baby Bio Organic, dilute seaweed; US: Espoma Indoor! or Neptune's Harvest fish & seaweed. Slow, gentle and hard to overdo.
Synthetic / liquid feeds
A general-purpose houseplant liquid at half strength — UK: Baby Bio, Westland Houseplant Feed or Phostrogen; US: Miracle-Gro Indoor Plant Food or Schultz. Convenient and fast-acting; the only risk is overdoing it.
Brand names are examples, not endorsements, and UK and US ranges differ — check the label’s own NPK and dilution rate, since formulations change.
Fertilising rock cress — frequently asked questions
What fertiliser does rock cress need?
A balanced general houseplant feed (roughly even N-P-K) is exactly right — it is grown for foliage, so steady, moderate nitrogen for healthy leaves is the goal, not a bloom or root formula. Rock Cress is an easy, light foliage feeder — a half-strength balanced liquid feed through the growing months keeps it green without forcing weak, sappy growth.
How often should I feed rock cress?
A light dressing of balanced, slow-release fertiliser in early spring is optional and sufficient. Avoid high-nitrogen feeds which produce excessive leafy growth. Lean soils naturally keep plants compact and floriferous. A light dressing of balanced, slow-release fertiliser in early spring is optional and sufficient. Avoid high-nitrogen feeds which produce excessive leafy growth. Lean soils naturally keep plants compact and floriferous. Treat that as sparingly through the growing season between spring through early autumn (roughly March to September); ease off in autumn and stop entirely in the low light of winter.
What strength of feed for rock cress?
Half strength is the safe default for rock cress — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
What does over-feeding rock cress look like?
Brown, crispy leaf tips and edges with no sign of underwatering. A white, crusty salt deposit on the soil surface or pot rim. Weak, pale, stretched new growth that flops. Lower leaves yellow and drop while the soil is correctly watered. Feeding rock cress year-round on a fixed schedule, including dark winter months, is the most common mistake — it cannot use the nutrients in low light and the surplus simply burns the roots and crusts the soil.
Should I flush the soil of rock cress?
Flush the pot of rock cress with plain water until it runs freely from the base every couple of months in the feeding season — it washes out the fertiliser salts that cause brown tips.
Keep reading
- Rock Cress care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water rock cress — the watering schedule
- The houseplant fertiliser schedule — feeding through the year
- NPK ratio explained — what the three numbers on the bottle mean
- How to fertilise chinese witch hazel
- How to fertilise jelena witch hazel
- How to fertilise mountain laurel
- All 8452 fertilising guides in the Growli library