Repotting guide

When & how to repot Kauri (Agathis australis)

Also called Kauri, New Zealand Kauri.

More about kauri

About Kauri

Agathis australis · also called Kauri, New Zealand Kauri · flowering

Kauri is one of the world's most impressive and ancient conifers, native to the warm-temperate forests of New Zealand's Northland. It produces a massive straight trunk with smooth, grey-brown flaking bark and leathery, strap-like leaves. It demands frost-free conditions and is grown in temperate climates only under glass. Sacred to Maori culture and critically threatened in the wild by kauri dieback disease.

Mature size: Up to 40–50 m tall and 3–5 m trunk diameter in the wild; under glass, typically 2–4 m in containers; slow-growing

Watch for — Kauri dieback disease (Phytophthora agathidicida): A devastating water mould specific to kauri, causing root and collar rot, yellowing foliage, and death. Spread through contaminated soil on boots and tools. In cultivation, use sterile substrate, avoid reusing soil from infected sites, and clean pots thoroughly. No cure exists — biosecurity is critical.

How to tell kauri needs repotting

Repotting on a calendar is less reliable than reading the plant. For kauri, 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 kauri 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 kauri

Every 2–3 years; top-dress in the in-between years. Kauri's growth habit — broadly conical when young, developing a massive straight cylindrical trunk with a high domed canopy of spreading branches; trunk clear of branches for much of its height at maturity — sets the pace. Kauri is one of the world's most impressive and ancient conifers, native to the warm-temperate forests of New Zealand's Northland. It produces a massive straight trunk with smooth, grey-brown flaking bark and leathery, strap-like leaves. It demands frost-free conditions and is grown in temperate climates only under glass. Sacred to Maori culture and critically threatened in the wild by kauri dieback disease.

What size pot to step kauri up to

Move up exactly one pot size. A heavy kauri 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 kauri

Early spring, just as new growth restarts, is the ideal window for kauri. 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 kauri

Consider top-dressing first. If kauri 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 well-drained, fertile, acidic soil with high organic matter; ph 4.5–6.5 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 kauri in the same spot and light — moving and repotting at once is what makes it drop leaves.

Aftercare

Leave kauri 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 kauri

Kauri wants well-drained, fertile, acidic soil with high organic matter; ph 4.5–6.5. In the wild, kauri grows on ancient, deeply weathered, low-nutrient soils. In cultivation, use a peat-free, loam-based compost (e.g. John Innes No. 2 or 3) with added fine bark and perlite to ensure excellent drainage and aeration. Avoid alkaline or nutrient-saturated composts. The root zone must never be compacted or walked on. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting kauri — frequently asked questions

How often should you repot kauri?

Every 2–3 years; top-dress in the in-between years for kauri. Fully repot kauri 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 well-drained, fertile, acidic soil with high organic matter; ph 4.5–6.5. It is heavy and hates being moved, and a vastly oversized pot holds water against the roots and rots them.

What size pot does kauri need?

When is the best time of year to repot kauri?

Should you top-dress or fully repot kauri?

For a big, heavy kauri, 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 kauri after repotting?

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