Fertilising guide
How to fertilise Langsat (Lansium parasiticum)— schedule & NPK
Also called Langsat, Duku, Longkong, Lanzones.
More about langsat
About Langsat
Lansium parasiticum · also called Langsat, Duku · tropical
Langsat is a beloved Southeast Asian fruit tree bearing clusters of round, translucent-fleshed fruits with a sweet-tart, lychee-like flavour. A shade-tolerant understorey tree in nature, it adapts well to humid tropical gardens and performs best in deep, fertile, well-drained soils. The 'Longkong' type has thicker skin that does not ooze latex, making it easier to eat.
Growth habit: Slender, upright tree with a narrow, slightly drooping canopy; fruits in pendulous clusters on older wood and branches
Watch for — Fruit drop before maturity: Premature fruit drop is linked to water stress, nutrient deficiency (especially potassium and boron), or pest pressure during fruit set. Maintain consistent irrigation, apply foliar boron at fruit set, and monitor for fruit-boring insects. Mulching reduces soil temperature fluctuations that stress the root system.
What fertiliser langsat actually wants — and why
Langsat 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 langsat: 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 langsat, 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 langsat:
Apply a balanced NPK fertiliser (e.g. 8-8-8 or 12-12-17) every 2–3 months during the active growing season. Switch to a low-nitrogen, high-potassium formula as flowering approaches. Organic compost applications twice yearly improve soil biology and long-term fertility. 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 langsat 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 langsat
Half strength is the safe default for langsat — 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 langsat first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the langsat watering schedule.
Signs you are over-feeding langsat
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for langsat:
- 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 langsat
- 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 langsat care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Flush the pot of langsat 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 langsat
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 langsat — frequently asked questions
What fertiliser does langsat 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. Langsat 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 langsat?
Apply a balanced NPK fertiliser (e.g. 8-8-8 or 12-12-17) every 2–3 months during the active growing season. Switch to a low-nitrogen, high-potassium formula as flowering approaches. Organic compost applications twice yearly improve soil biology and long-term fertility. Apply a balanced NPK fertiliser (e.g. 8-8-8 or 12-12-17) every 2–3 months during the active growing season. Switch to a low-nitrogen, high-potassium formula as flowering approaches. Organic compost applications twice yearly improve soil biology and long-term fertility. 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 langsat?
Half strength is the safe default for langsat — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
What does over-feeding langsat 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 langsat 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 langsat?
Flush the pot of langsat 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
- Langsat care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water langsat — 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 holmgren's dioon
- How to fertilise tomaselli's dioon
- How to fertilise broad-leaf horncone
- All 8452 fertilising guides in the Growli library