Repotting guide

When & how to repot Gunnera manicata (Gunnera manicata)

Also called Giant Rhubarb, Brazilian Giant Rhubarb, Prickly Rhubarb.

More about gunnera manicata

About Gunnera manicata

Gunnera manicata · also called Giant Rhubarb, Brazilian Giant Rhubarb · flowering

Gunnera manicata is a spectacular architectural giant from Brazil, grown for its enormous prickly-stalked, rhubarb-like leaves that can span over a metre and a half across. Massed conical flower spikes appear at the base in summer. A dramatic specimen for permanently wet streamsides and bog gardens, it needs deep moisture, shelter and, in cold areas, winter crown protection to survive.

Mature size: 2-2.5 m tall and 3-4 m or more across when fully established; individual leaves can exceed 1.5 m wide.

Watch for — Drought collapse: If the soil dries, the enormous leaves wilt and brown rapidly. Permanent moisture at the roots is essential; site it where water is guaranteed.

How to tell gunnera manicata needs repotting

Repotting on a calendar is less reliable than reading the plant. For gunnera manicata, 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 gunnera manicata) 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 gunnera manicata

Only every 2–4 years, when genuinely crowded. Gunnera manicata 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. Massive clump-forming, rhizomatous herbaceous perennial; a crown of giant, deeply lobed, prickly-stalked leaves expands each season into an imposing mound, dying back to the crown in winter in temperate climates..

What size pot to step gunnera manicata up to

Go up only one pot size — roughly 2–3 cm (about an inch) wider in diameter, no more. Gunnera manicata 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 gunnera manicata 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 gunnera manicata

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

Confirm it actually needs it. Slide gunnera manicata 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 gunnera manicata 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 deep, rich, permanently moist loam, 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 gunnera manicata 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 gunnera manicata

Gunnera manicata wants deep, rich, permanently moist loam. Demands a deep, fertile, humus-rich soil that never dries, ideally at a pond or stream margin. Incorporate generous organic matter. It is a heavy feeder and grows largest in boggy, nutrient-rich ground. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting gunnera manicata — frequently asked questions

How often should you repot gunnera manicata?

Only every 2–4 years, when genuinely crowded for gunnera manicata. Only repot gunnera manicata 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 deep, rich, permanently moist loam. The key mistake is over-potting: a too-big pot stays wet and rots the roots.

What size pot does gunnera manicata need?

When is the best time of year to repot gunnera manicata?

Does gunnera manicata like to be root-bound?

Yes — gunnera manicata 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 gunnera manicata after repotting?

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