Repotting guide

When & how to repot Rex begonia (Begonia rex)

Also called painted-leaf begonia, king begonia.

About Rex begonia

Begonia rex · also called painted-leaf begonia, king begonia · houseplant

Rex begonia is grown for spectacular silver, purple, pink, and green foliage rather than flowers. It needs even moisture, high humidity, and bright indirect light and is more demanding than easier types like wax begonias. Toxic to pets if eaten.

The painted-leaf rex begonia (Begonia rex-cultorum hybrids) descends from Begonia rex, native to the humid forests of Assam in north-east India, introduced to England in 1856; it is a rhizomatous begonia whose thickened surface stem stores water and fuels the foliage.

Use a light, airy, well-drained mix and a shallow/wide pot, because the rhizome creeps across the surface rather than diving deep; compact wet soil is the main cause of decline.

Mature size: 30 cm tall and wide

Sources: aspca.org, homegarden.cahnr.uconn.edu, gardenerspath.com

How to tell rex begonia needs repotting

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

Only every 2–4 years, when genuinely crowded. Rex begonia 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. Rhizomatous foliage perennial.

What size pot to step rex begonia up to

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

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

Confirm it actually needs it. Slide rex begonia 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 rex begonia 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 light, peat-free potting mix with perlite, 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 rex begonia 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 rex begonia

Rex begonia wants light, peat-free potting mix with perlite. A light moisture-retentive mix with 20-30% perlite. Rhizomatous rex roots are shallow, so wide shallow pots suit them. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting rex begonia — frequently asked questions

How often should you repot rex begonia?

Only every 2–4 years, when genuinely crowded for rex begonia. Only repot rex begonia 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 light, peat-free potting mix with perlite. The key mistake is over-potting: a too-big pot stays wet and rots the roots.

What size pot does rex begonia need?

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

Does rex begonia like to be root-bound?

Yes — rex begonia 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 rex begonia after repotting?

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