Fertilising guide
How to fertilise Large Bitter-cress (Cardamine amara)— schedule & NPK
Also called Large Bitter-cress, Large Bittercress.
More about large bitter-cress
About Large Bitter-cress
Cardamine amara · also called Large Bitter-cress, Large Bittercress · edible
Cardamine amara is a native European perennial of the mustard family (Brassicaceae), found along the margins of streams, wet meadows, and alder carr in the UK and across temperate Europe, distinctive for its purple (not white) anthers. It prefers constantly wet, humus-rich soil in partial shade and will not tolerate drought. The leaves have an edible, peppery-bitter watercress-like flavour and can be used raw or cooked, but harvest only from uncontaminated, clean-water sites. No ASPCA data is available for this species; it is classified as mildly-toxic as a precaution since Brassicaceae plants contain glucosinolates that can cause mild gastrointestinal irritation in pets.
Growth habit: Upright to spreading perennial, growing from a creeping rhizome, with pinnate leaves and racemes of small white four-petalled flowers with distinctive purple anthers in April to June.
What fertiliser large bitter-cress actually wants — and why
Large Bitter-cress feeds in two distinct phases — balanced to build the plant, then high-potassium the moment flowering starts to set and fill a heavy crop.
Balanced (even N-P-K) at planting for roots and frame, then switch to a high-potassium ("high-potash") tomato-style feed once the first flowers open — potassium is what sizes and ripens fruit, not nitrogen.
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 large bitter-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 large bitter-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 large bitter-cress:
No supplementary feeding needed in naturally fertile riparian soil; in garden beds, an annual mulch of well-rotted compost in autumn is sufficient. So: a balanced feed or compost at planting, then a high-potash liquid every 1-2 weeks from first flower through harvest across the main season (spring through early autumn).
The dormant-season rule matters more than the exact interval: skip feeding entirely when large bitter-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 large bitter-cress
Follow the crop-feed label rate for large bitter-cress — these are calibrated for hungry vegetables. Consistency through fruiting matters more than strength; erratic feeding causes problems like blossom-end rot.
Feeding always goes onto already-damp soil, never dry roots — water large bitter-cress first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the large bitter-cress watering schedule.
Signs you are over-feeding large bitter-cress
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for large bitter-cress:
- Vigorous dark-green leafy growth but few flowers or fruit (excess nitrogen).
- Lush foliage hiding the crop; soft growth prone to pests and disease.
- Salt crust on the soil and scorched leaf edges in containers.
Signs you are under-feeding large bitter-cress
- Pale, yellowing lower leaves and stunted growth.
- Small fruit, poor set, and a quickly exhausted plant.
- Blossom-end rot and weak cropping from erratic or insufficient feeding.
If the symptoms point at watering, light or roots rather than nutrition, the full large bitter-cress care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
In containers, fertiliser salts build up fast — water large bitter-cress thoroughly so excess drains from the base each time, and flush pots with plain water every few weeks to prevent a damaging salt build-up.
Organic vs synthetic feeds for large bitter-cress
Organic options
Garden compost or well-rotted manure dug in before planting, plus a liquid comfrey or seaweed feed once fruiting starts. UK: comfrey feed or organic Tomorite; US: Espoma Tomato-tone or Neptune's Harvest. Builds soil and feeds in one.
Synthetic / liquid feeds
A balanced feed at planting then a high-potash tomato feed in fruiting — UK: Growmore at planting then Tomorite (Levington) or Phostrogen; US: a balanced 10-10-10 then Miracle-Gro Tomato or a bloom booster.
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 large bitter-cress — frequently asked questions
What fertiliser does large bitter-cress need?
Balanced (even N-P-K) at planting for roots and frame, then switch to a high-potassium ("high-potash") tomato-style feed once the first flowers open — potassium is what sizes and ripens fruit, not nitrogen. Large Bitter-cress feeds in two distinct phases — balanced to build the plant, then high-potassium the moment flowering starts to set and fill a heavy crop.
How often should I feed large bitter-cress?
No supplementary feeding needed in naturally fertile riparian soil; in garden beds, an annual mulch of well-rotted compost in autumn is sufficient. No supplementary feeding needed in naturally fertile riparian soil; in garden beds, an annual mulch of well-rotted compost in autumn is sufficient. So: a balanced feed or compost at planting, then a high-potash liquid every 1-2 weeks from first flower through harvest across the main season (spring through early autumn).
What strength of feed for large bitter-cress?
Follow the crop-feed label rate for large bitter-cress — these are calibrated for hungry vegetables. Consistency through fruiting matters more than strength; erratic feeding causes problems like blossom-end rot.
What does over-feeding large bitter-cress look like?
Vigorous dark-green leafy growth but few flowers or fruit (excess nitrogen). Lush foliage hiding the crop; soft growth prone to pests and disease. Salt crust on the soil and scorched leaf edges in containers. Staying on a high-nitrogen feed once large bitter-cress starts flowering is the classic error — you get a huge leafy plant and a disappointing crop. Switch to high-potash the moment flowers appear.
Should I flush the soil of large bitter-cress?
In containers, fertiliser salts build up fast — water large bitter-cress thoroughly so excess drains from the base each time, and flush pots with plain water every few weeks to prevent a damaging salt build-up.
Keep reading
- Large Bitter-cress care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water large bitter-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 american persimmon
- How to fertilise chocolate persimmon
- How to fertilise ichi ki kei jiro persimmon
- All 10153 fertilising guides in the Growli library