Repotting guide

When & how to repot Begonia grandis (Begonia grandis)

Also called hardy begonia, Chinese begonia, Evans begonia.

More about begonia grandis

About Begonia grandis

Begonia grandis · also called hardy begonia, Chinese begonia · flowering

Begonia grandis is the only begonia reliably winter-hardy in the open ground, surviving to USDA Zone 6. This tuberous species forms upright, branching stems to 60 cm topped with airy clusters of pink flowers from midsummer to autumn, with red-backed wing-shaped leaves. It dies back each winter and self-sows from leaf-axil bulbils.

Mature size: 45-60 cm tall and 30-45 cm wide

How to tell begonia grandis needs repotting

Repotting on a calendar is less reliable than reading the plant. For begonia grandis, 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 begonia grandis) 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 begonia grandis

Only every 2–4 years, when genuinely crowded. Begonia grandis 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. Upright, branching herbaceous perennial that emerges late in spring, blooms midsummer to first frost, then dies back to dormant tubers; spreads gently via dropped axillary bulbils..

What size pot to step begonia grandis up to

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

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

Confirm it actually needs it. Slide begonia grandis 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 begonia grandis 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 humus-rich, moist but free-draining woodland 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 begonia grandis 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 begonia grandis

Begonia grandis wants humus-rich, moist but free-draining woodland soil. Loose, leaf-mould-rich, slightly acidic to neutral soil that drains freely. Heavy wet clay in winter kills the dormant tubers; amend with grit and organic matter. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting begonia grandis — frequently asked questions

How often should you repot begonia grandis?

Only every 2–4 years, when genuinely crowded for begonia grandis. Only repot begonia grandis 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 humus-rich, moist but free-draining woodland soil. The key mistake is over-potting: a too-big pot stays wet and rots the roots.

What size pot does begonia grandis need?

When is the best time of year to repot begonia grandis?

Does begonia grandis like to be root-bound?

Yes — begonia grandis 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 begonia grandis after repotting?

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