Repotting guide

When & how to repot Langsat (Lansium parasiticum)

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.

Mature size: 10–15 m tall (33–50 ft); spread 4–7 m

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.

How to tell langsat needs repotting

Repotting on a calendar is less reliable than reading the plant. For langsat, watch for these signs:

Thick roots out of the drainage holes, or circling the surface and lifting the plant.
The pot dries out unusually fast and langsat wilts between waterings it used to shrug off.
The plant is visibly top-heavy and tips over easily.
Stalled growth and small new leaves over a full season — though with a big specimen, top-dressing is often the better first response before a full repot.

For the underlying biology of a pot-bound root system and why it stalls a plant, see our guide to spotting and fixing a root-bound plant.

How often to repot langsat

Every 2–3 years; top-dress in the in-between years. Langsat's growth habit — slender, upright tree with a narrow, slightly drooping canopy; fruits in pendulous clusters on older wood and branches — sets the pace. 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.

What size pot to step langsat up to

Move up exactly one pot size. A heavy langsat dropped into a vastly bigger pot sits in a reservoir of wet soil its roots cannot reach, which rots them and destabilises the plant. In the years between repots, lift off and replace the top 3–5 cm of soil (top-dressing) instead — it refreshes nutrients without the shock of a full repot.

Not sure of the exact diameter? Our pot size calculator takes the current pot and root spread and tells you the right next size — it deliberately recommends a single step up, never a big jump.

The best time of year to repot langsat

Early spring, just as new growth restarts, is the ideal window for langsat. The plant is moving into its strongest growth phase and re-roots into fresh soil quickly. Avoid repotting in winter dormancy or, for flowering plants, while it is in bud or bloom — recovery is slowest then and you risk dropping the flowers.

Step-by-step: repotting langsat

Consider top-dressing first. If langsat is not badly root-bound, scrape off and replace the top 3–5 cm of soil instead — far less shock for a big plant that hates moving.
Get help and one size up. For a full repot, choose a pot just one size larger. A heavy plant needs two people and a stable, free-draining pot.
Ease it out on its side. Lay the plant down, slide the pot off, and gently loosen the outer roots. Do not bare-root a mature specimen.
Repot at the same depth. Add fresh deep, well-drained clay loam or sandy clay loam, rich in organic matter beneath and around the rootball, keeping the original soil line. Firm it so the trunk is stable and upright.
Water and leave it put. Water thoroughly, then leave langsat in the same spot and light — moving and repotting at once is what makes it drop leaves.

Aftercare

Leave langsat in exactly the same spot and light it was in before — moving and repotting at the same time is what makes a big specimen drop leaves. Water it in well, then let the top of the soil dry before watering again so the larger volume of fresh soil does not stay sodden. Do not fertilise for about 4 weeks — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.

The right soil mix for langsat

Langsat wants deep, well-drained clay loam or sandy clay loam, rich in organic matter. Thrives in deep, fertile, slightly acidic soil (pH 5.5–6.5). Intolerant of waterlogging — root aeration is critical. Mulch the root zone generously with wood chips or compost to retain moisture, regulate temperature, and suppress weeds without compacting soil around the trunk. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting langsat — frequently asked questions

How often should you repot langsat?

Every 2–3 years; top-dress in the in-between years for langsat. Fully repot langsat only every 2–3 years; in the in-between years just top-dress the top 3–5 cm of soil. Step up one pot size in spring with deep, well-drained clay loam or sandy clay loam, rich in organic matter. It is heavy and hates being moved, and a vastly oversized pot holds water against the roots and rots them.

What size pot does langsat need?

When is the best time of year to repot langsat?

Should you top-dress or fully repot langsat?

For a big, heavy langsat, top-dressing — replacing the top 3–5 cm of soil — is the gentler option most years, with a full repot only every 2–3 years. A mature specimen sulks and drops leaves when fully repotted, so do it as rarely as the roots allow.

Should you fertilise langsat after repotting?

Not immediately. Wait about 4 weeks after repotting langsat. Fresh mix already contains nutrients, and feeding freshly cut or disturbed roots burns them. Resume your normal feeding routine once you see new growth.