Fertilising guide
How to fertilise Tuberous Cranesbill (Geranium tuberosum)— schedule & NPK
Also called Tuberous Cranesbill, Tuberous-Rooted Cranesbill.
More about tuberous cranesbill
About Tuberous Cranesbill
Geranium tuberosum · also called Tuberous Cranesbill, Tuberous-Rooted Cranesbill · flowering
Geranium tuberosum is a spring-flowering cranesbill native to the Mediterranean basin east to Iran, growing from small underground tubers. It behaves like a spring ephemeral: finely divided foliage emerges in late winter, lilac-pink veined flowers appear in spring, and the whole plant retreats into summer dormancy by early summer. The most important care fact is to provide a sunny, sharply drained position and allow the soil to dry out completely in summer — wet summer soils rot the tubers. ASPCA's toxic 'Geranium' entry refers to Pelargonium; true Geranium cranesbills are not individually listed as toxic, but ASPCA does not confirm them as non-toxic either, so treat with caution around pets.
Growth habit: Tuberous-rooted clump-forming geranium with a spring ephemeral habit, dying back to underground tubers by early summer.
Watch for — Geranium sawfly: Greyish-green larvae feed on leaves in spring, leaving ragged holes; check undersides of leaves regularly and remove larvae by hand.
What fertiliser tuberous cranesbill actually wants — and why
Tuberous Cranesbill 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 tuberous cranesbill: 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 tuberous cranesbill, 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 tuberous cranesbill:
Apply a low-nitrogen, high-potassium liquid feed once or twice in early spring just as foliage emerges; no feeding is needed once dormancy begins. 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 tuberous cranesbill 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 tuberous cranesbill
Half strength is the safe default for tuberous cranesbill — 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 tuberous cranesbill first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the tuberous cranesbill watering schedule.
Signs you are over-feeding tuberous cranesbill
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for tuberous cranesbill:
- 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 tuberous cranesbill
- 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 tuberous cranesbill care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Flush the pot of tuberous cranesbill 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 tuberous cranesbill
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 tuberous cranesbill — frequently asked questions
What fertiliser does tuberous cranesbill 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. Tuberous Cranesbill 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 tuberous cranesbill?
Apply a low-nitrogen, high-potassium liquid feed once or twice in early spring just as foliage emerges; no feeding is needed once dormancy begins. Apply a low-nitrogen, high-potassium liquid feed once or twice in early spring just as foliage emerges; no feeding is needed once dormancy begins. 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 tuberous cranesbill?
Half strength is the safe default for tuberous cranesbill — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
What does over-feeding tuberous cranesbill 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 tuberous cranesbill 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 tuberous cranesbill?
Flush the pot of tuberous cranesbill 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
- Tuberous Cranesbill care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water tuberous cranesbill — 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 lesser quaking grass
- How to fertilise wood melick
- How to fertilise purple siberian melic
- All 10153 fertilising guides in the Growli library