Repotting guide

When & how to repot Mountain Rimu (Dacrydium bidwillii)

Also called Bog Pine, Mountain Pine, New Zealand Mountain Rimu.

More about mountain rimu

About Mountain Rimu

Dacrydium bidwillii · also called Bog Pine, Mountain Pine · flowering

Mountain Rimu is a compact, slow-growing podocarp conifer native to the montane and subalpine zones of New Zealand's North and South Islands. It forms a low, spreading shrub with fine, scale-like leaves. Hardy and moisture-tolerant, it suits cool temperate gardens and rock gardens. It is not on the ASPCA toxic plants list.

Mature size: 0.3-1.5 m tall, spreading to 1-2 m wide

Watch for — Root rot in heavy clay: Improve drainage by incorporating grit into planting hole and mound planting if needed.

How to tell mountain rimu needs repotting

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

Roots spiralling thickly out of the drainage holes or pushing the whole plant up out of the pot.
The pot is so packed that water runs straight through in seconds and barely wets the soil.
It has split a plastic pot, or the rootball is a solid mass with almost no soil left when you slide it out.
Growth and (for mountain rimu) flowering have clearly stalled despite good light and feeding — but remember this plant likes being snug, so a little crowding alone is not a reason to 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 mountain rimu

Only every 2–4 years, when genuinely crowded. Mountain Rimu is one of the plants that genuinely prefers a snug pot — it grows and flowers better with its roots a little restricted, so resist the urge to repot it on schedule. Low-spreading, shrubby evergreen podocarp.

What size pot to step mountain rimu up to

Go up only one pot size — roughly 2–3 cm (about an inch) wider in diameter, no more. Mountain Rimu positively prefers a snug pot: it flowers and grows better when the roots are a little restricted. The single biggest repotting mistake here is over-potting — dropping mountain rimu into a pot two or three sizes up. All that surplus soil holds water the small root system cannot use, stays cold and wet, and rots the roots within weeks. When in doubt, choose the smaller pot.

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 mountain rimu

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

Confirm it actually needs it. Slide mountain rimu out and check the roots. Only continue if it is genuinely packed — this plant prefers a snug pot, so if there is still soil and room, put it straight back.
Pick a pot only one size up. Choose a pot just 2–3 cm wider with good drainage. Resist anything bigger; over-potting is the main killer here.
Ease it out gently. Water lightly the day before, then tip mountain rimu out, supporting the base. Tease the outer roots free only enough to stop them circling.
Repot at the same depth. Add a layer of fresh moist, peaty, acidic, well-aerated soil, set the plant so the soil line sits exactly where it did before, and backfill around the sides, firming lightly.
Settle it in. Water once to settle the soil, then let it sit. Hold off on more water until the top of the soil dries — fresh soil around a small root system stays wet for a while.

Aftercare

Because the new soil holds more water than the old crammed rootball did, ease right back on watering — let the top of the soil dry before you water mountain rimu again, or you will rot the roots in the very pot you just moved it to. Keep it out of harsh direct sun for a fortnight. Do not fertilise for about 4 weeks — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.

The right soil mix for mountain rimu

Mountain Rimu wants moist, peaty, acidic, well-aerated soil. Prefers acidic conditions (pH 4.5–6.0) rich in organic matter. A mix of peat substitute, bark, and grit replicates its native habitat. Avoid alkaline or compacted soils. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting mountain rimu — frequently asked questions

How often should you repot mountain rimu?

Only every 2–4 years, when genuinely crowded for mountain rimu. Only repot mountain rimu every 2–4 years, and only when it is genuinely root-bound — it flowers and grows best slightly crowded. Step up just one pot size in spring using moist, peaty, acidic, well-aerated soil. The key mistake is over-potting: a too-big pot stays wet and rots the roots.

What size pot does mountain rimu need?

When is the best time of year to repot mountain rimu?

Does mountain rimu like to be root-bound?

Yes — mountain rimu genuinely flowers and grows best when slightly pot-bound, so do not rush to repot it. The mistake to avoid is over-potting into a much larger pot: the excess soil stays wet, the roots cannot use it, and the plant rots. Only repot every few years and only one snug size up.

Should you fertilise mountain rimu after repotting?

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