Fertilising guide
How to fertilise Hairy Rock-cress (Arabis hirsuta)— schedule & NPK
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.
Growth habit: 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 fertiliser hairy rock-cress actually wants — and why
Hairy 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 hairy 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 hairy 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 hairy rock-cress:
No fertilising required or beneficial; this species is adapted to infertile substrates and feeding promotes soft, floppy growth that is susceptible to disease. 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 hairy 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 hairy rock-cress
Half strength is the safe default for hairy 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 hairy 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 hairy rock-cress watering schedule.
Signs you are over-feeding hairy rock-cress
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for hairy 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 hairy 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 hairy rock-cress care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Flush the pot of hairy 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 hairy 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 hairy rock-cress — frequently asked questions
What fertiliser does hairy 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. Hairy 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 hairy rock-cress?
No fertilising required or beneficial; this species is adapted to infertile substrates and feeding promotes soft, floppy growth that is susceptible to disease. No fertilising required or beneficial; this species is adapted to infertile substrates and feeding promotes soft, floppy growth that is susceptible to disease. 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 hairy rock-cress?
Half strength is the safe default for hairy 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 hairy 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 hairy 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 hairy rock-cress?
Flush the pot of hairy 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
- Hairy Rock-cress care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water hairy rock-cress — the watering schedule
- The houseplant fertiliser schedule — feeding through the year
- NPK ratio explained — what the three numbers on the bottle mean
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- How to fertilise ginkgo 'mariken'
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- All 10153 fertilising guides in the Growli library