Fertilising guide
How to fertilise Long-leaved Pelargonium (Pelargonium longifolium)— schedule & NPK
Also called Long-leaved Pelargonium, Long-leaf Geranium.
More about long-leaved pelargonium
About Long-leaved Pelargonium
Pelargonium longifolium · also called Long-leaved Pelargonium, Long-leaf Geranium · flowering
Pelargonium longifolium is a tuberous geophyte native to the arid and semi-arid zones of South Africa's Western Cape, producing narrow, strap-shaped leaves and pale cream to yellowish flowers marked with dark purple veins. As a summer-dormant bulb-like plant it follows a Mediterranean rhythm — grow in autumn and winter, rest in summer — and demands excellent drainage and minimal water during dormancy. The single most important care fact is to withhold almost all water in summer when the plant is leafless, or the tuber will rot. Toxic to cats, dogs, and horses.
Growth habit: Deciduous tuberous geophyte; narrow leaves emerge from a knobbly rootstock in autumn, the plant flowers in late winter to spring, then dies back to the tuber in summer.
What fertiliser long-leaved pelargonium actually wants — and why
Long-leaved Pelargonium 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 long-leaved pelargonium: 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 long-leaved pelargonium, 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 long-leaved pelargonium:
Apply a dilute, balanced fertiliser monthly during the growing season (autumn to spring) and stop completely during summer dormancy. Treat that as monthly 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 long-leaved pelargonium 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 long-leaved pelargonium
Half strength is the safe default for long-leaved pelargonium — 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 long-leaved pelargonium first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the long-leaved pelargonium watering schedule.
Signs you are over-feeding long-leaved pelargonium
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for long-leaved pelargonium:
- 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 long-leaved pelargonium
- 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 long-leaved pelargonium care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Flush the pot of long-leaved pelargonium 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 long-leaved pelargonium
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 long-leaved pelargonium — frequently asked questions
What fertiliser does long-leaved pelargonium 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. Long-leaved Pelargonium 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 long-leaved pelargonium?
Apply a dilute, balanced fertiliser monthly during the growing season (autumn to spring) and stop completely during summer dormancy. Apply a dilute, balanced fertiliser monthly during the growing season (autumn to spring) and stop completely during summer dormancy. Treat that as monthly 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 long-leaved pelargonium?
Half strength is the safe default for long-leaved pelargonium — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
What does over-feeding long-leaved pelargonium 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 long-leaved pelargonium 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 long-leaved pelargonium?
Flush the pot of long-leaved pelargonium 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
- Long-leaved Pelargonium care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water long-leaved pelargonium — 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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