Fertilising guide

How to fertilise Geranium macrorrhizum (Geranium macrorrhizum)— schedule & NPK

Also called Bigroot geranium, Rock cranesbill, Bulgarian geranium.

More about geranium macrorrhizum

About Geranium macrorrhizum

Geranium macrorrhizum · also called Bigroot geranium, Rock cranesbill · flowering

Geranium macrorrhizum is a tough, semi-evergreen hardy cranesbill grown as weed-smothering ground cover, with aromatic, sticky leaves that colour red in autumn and magenta-to-pink spring flowers. Spreading by thick rhizomes, it tolerates dry shade under trees where little else thrives. It is fully hardy, low-maintenance and largely pest- and drought-proof.

Growth habit: Low, rhizomatous, semi-evergreen ground-cover perennial spreading steadily to form dense, aromatic carpets of foliage.

What fertiliser geranium macrorrhizum actually wants — and why

Geranium macrorrhizum 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 macrorrhizum: 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 macrorrhizum, 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 macrorrhizum:

Practically self-sufficient; it grows well in poor soil. An optional spring mulch or light feed improves vigour on very impoverished ground, but feeding is rarely necessary. 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 macrorrhizum 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 macrorrhizum

Follow the flowering-feed label rate for geranium macrorrhizum, 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 macrorrhizum first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the geranium macrorrhizum watering schedule.

Signs you are over-feeding geranium macrorrhizum

Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for geranium macrorrhizum:

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 macrorrhizum

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 macrorrhizum care brief covers soil, humidity and the common problems for this species.

Flushing and leaching the salts

Container-grown geranium macrorrhizum 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 macrorrhizum

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 macrorrhizum — frequently asked questions

What fertiliser does geranium macrorrhizum 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 macrorrhizum 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 macrorrhizum?

Practically self-sufficient; it grows well in poor soil. An optional spring mulch or light feed improves vigour on very impoverished ground, but feeding is rarely necessary. Practically self-sufficient; it grows well in poor soil. An optional spring mulch or light feed improves vigour on very impoverished ground, but feeding is rarely necessary. 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 macrorrhizum?

What does over-feeding geranium macrorrhizum 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 macrorrhizum 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 macrorrhizum?