Fertilising guide
How to fertilise Geranium phaeum (Geranium phaeum)— schedule & NPK
Also called Dusky cranesbill, Mourning widow geranium, Black widow geranium.
More about geranium phaeum
About Geranium phaeum
Geranium phaeum · also called Dusky cranesbill, Mourning widow geranium · flowering
Geranium phaeum, the dusky cranesbill or mourning widow, is a clump-forming woodland perennial grown for its small, reflexed flowers in deep maroon-purple to near-black, held on slender stems above soft, often blotched leaves in late spring and early summer. One of the best hardy geraniums for shade and dry shade, it self-seeds gently and naturalises beautifully beneath trees and shrubs.
Growth habit: Upright clump-forming perennial that builds a basal rosette of soft leaves and sends up airy flowering stems; spreads gently and self-seeds.
What fertiliser geranium phaeum actually wants — and why
Geranium phaeum is a heavy-blooming flower with a big appetite — a regular high-potash feed through the season is what drives a long, dense display.
A high-potassium ("high-potash") flowering feed — tomato-style or a dedicated bloom/rose feed. Potassium powers flowering; a high-nitrogen feed gives you a leafy plant with disappointing bloom.
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 geranium phaeum: 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 geranium phaeum, 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 geranium phaeum:
Modest feeder. An annual spring mulch of leaf mould or compost meets its needs; heavy fertiliser is unnecessary and encourages lax foliage over flowers. For a hungry bloomer that means feeding regularly — sparingly through the growing season — right through flowering across the main season (spring through early autumn), tapering as blooming ends.
The dormant-season rule matters more than the exact interval: skip feeding entirely when geranium phaeum 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 geranium phaeum
Follow the flowering-feed label rate for geranium phaeum, or half strength if feeding very frequently. These plants genuinely use the nutrients — under-feeding shows up fast as a thin display.
Feeding always goes onto already-damp soil, never dry roots — water geranium phaeum first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the geranium phaeum watering schedule.
Signs you are over-feeding geranium phaeum
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for geranium phaeum:
- Lots of lush leaves but few flowers (too much nitrogen).
- Scorched leaf edges and salt crust from too-strong or too-frequent feeds.
- Soft, sappy growth prone to aphids and mildew.
Signs you are under-feeding geranium phaeum
- Sparse, small, short-lived flowers and pale foliage.
- A tired plant that stops blooming early in the season.
- Weak growth and poor repeat-flowering after the first flush.
If the symptoms point at watering, light or roots rather than nutrition, the full geranium phaeum care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Container-grown geranium phaeum accumulates feed salts fast with frequent feeding — water until it drains each time and flush pots with plain water every few weeks to prevent scorch.
Organic vs synthetic feeds for geranium phaeum
Organic options
A liquid comfrey or seaweed feed (naturally potassium-rich) plus compost or well-rotted manure as a mulch. UK: comfrey feed, organic Tomorite, or rose feed; US: Espoma Rose-tone or Neptune's Harvest. Feeds and improves soil.
Synthetic / liquid feeds
A high-potash flowering feed on a regular cadence — UK: Tomorite (Levington), Phostrogen or a specialist rose feed; US: Miracle-Gro Bloom Booster or a rose food. Fast, reliable bloom response.
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 geranium phaeum — frequently asked questions
What fertiliser does geranium phaeum need?
A high-potassium ("high-potash") flowering feed — tomato-style or a dedicated bloom/rose feed. Potassium powers flowering; a high-nitrogen feed gives you a leafy plant with disappointing bloom. Geranium phaeum is a heavy-blooming flower with a big appetite — a regular high-potash feed through the season is what drives a long, dense display.
How often should I feed geranium phaeum?
Modest feeder. An annual spring mulch of leaf mould or compost meets its needs; heavy fertiliser is unnecessary and encourages lax foliage over flowers. Modest feeder. An annual spring mulch of leaf mould or compost meets its needs; heavy fertiliser is unnecessary and encourages lax foliage over flowers. For a hungry bloomer that means feeding regularly — sparingly through the growing season — right through flowering across the main season (spring through early autumn), tapering as blooming ends.
What strength of feed for geranium phaeum?
Follow the flowering-feed label rate for geranium phaeum, or half strength if feeding very frequently. These plants genuinely use the nutrients — under-feeding shows up fast as a thin display.
What does over-feeding geranium phaeum look like?
Lots of lush leaves but few flowers (too much nitrogen). Scorched leaf edges and salt crust from too-strong or too-frequent feeds. Soft, sappy growth prone to aphids and mildew. Using a high-nitrogen general feed on geranium phaeum is the headline mistake — you grow a big leafy plant with few flowers. The second is simply under-feeding a genuinely hungry bloomer and getting a sparse, short display.
Should I flush the soil of geranium phaeum?
Container-grown geranium phaeum accumulates feed salts fast with frequent feeding — water until it drains each time and flush pots with plain water every few weeks to prevent scorch.
Keep reading
- Geranium phaeum care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water geranium phaeum — 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 peace lily
- How to fertilise bird of paradise
- How to fertilise hoya
- All 5561 fertilising guides in the Growli library