Fertilising guide
How to fertilise Rex begonia (Begonia rex)— schedule & NPK
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.
Feed lightly with a dilute balanced fertiliser during active growth only; it is a comparatively fussy, slow grower and reacts to overfeeding and low humidity with crisped leaf edges rather than vigour.
Growth habit: Rhizomatous foliage perennial
Sources: aspca.org, homegarden.cahnr.uconn.edu, gardenerspath.com
What fertiliser rex begonia actually wants — and why
Rex begonia is a genuinely hungry tropical — in bright warmth it pushes growth fast and rewards a regular half-strength balanced feed all season.
A balanced liquid feed (even N-P-K) or a slightly nitrogen-leaning foliage feed — this is a big-leaved foliage plant putting on real size, so it wants steady nitrogen for lush leaves, not a bloom formula.
For the language behind the three numbers on the bottle — what nitrogen, phosphorus and potassium each do — see the NPK ratio explained entry. The short version for rex begonia: match the feed to the job the plant is doing right now, not to a generic “plant food” on the shelf.
How often to feed rex begonia, and which months
Feeding only earns its keep while the plant is in active growth and can use the nutrients — pour feed into a dormant or low-light plant and it simply builds up as root-burning salt. For rex begonia:
Quarter-strength balanced feed every 3-4 weeks during the growing season. For a fast grower like this that means feeding regularly — about every 3-4 weeks — right through spring through early autumn (roughly March to September), tapering off only as light drops in autumn.
The dormant-season rule matters more than the exact interval: skip feeding entirely when rex begonia is resting. For the wider context on indoor feeding rhythms across the seasons, the houseplant fertiliser schedule walks through the year month by month.
What strength to mix for rex begonia
Half strength every feed is the sweet spot for rex begonia: frequent enough to fuel fast growth, dilute enough that it never scorches even when you feed often.
Feeding always goes onto already-damp soil, never dry roots — water rex begonia first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the rex begonia watering schedule.
Signs you are over-feeding rex begonia
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for rex begonia:
- Brown, scorched leaf tips and margins despite correct watering.
- A white salt crust on the soil or around the pot edge.
- Sudden leaf yellowing and drop shortly after a strong feed.
- Soft, weak, over-stretched growth that cannot support itself.
Signs you are under-feeding rex begonia
- New leaves coming in noticeably smaller than older ones.
- Pale, yellow-green older leaves and slow growth through peak summer.
- A general loss of vigour and gloss in a plant that should be racing away.
If the symptoms point at watering, light or roots rather than nutrition, the full rex begonia care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Because you feed often, salts accumulate faster — flush the pot of rex begonia with plain water until it drains freely roughly every month through the feeding season to keep the root zone clean.
Organic vs synthetic feeds for rex begonia
Organic options
A diluted seaweed or fish-and-seaweed feed plus a yearly top-dress of worm castings supports fast growth without burn risk. UK: Westland seaweed or Baby Bio Organic; US: Neptune's Harvest or Espoma Indoor!.
Synthetic / liquid feeds
A balanced houseplant liquid at half strength applied frequently — UK: Baby Bio, Phostrogen or Westland Houseplant Feed; US: Miracle-Gro Indoor Plant Food or Dyna-Gro Foliage-Pro for steady leafy growth.
Brand names are examples, not endorsements, and UK and US ranges differ — check the label’s own NPK and dilution rate, since formulations change.
Fertilising rex begonia — frequently asked questions
What fertiliser does rex begonia need?
A balanced liquid feed (even N-P-K) or a slightly nitrogen-leaning foliage feed — this is a big-leaved foliage plant putting on real size, so it wants steady nitrogen for lush leaves, not a bloom formula. Rex begonia is a genuinely hungry tropical — in bright warmth it pushes growth fast and rewards a regular half-strength balanced feed all season.
How often should I feed rex begonia?
Quarter-strength balanced feed every 3-4 weeks during the growing season. Quarter-strength balanced feed every 3-4 weeks during the growing season. For a fast grower like this that means feeding regularly — about every 3-4 weeks — right through spring through early autumn (roughly March to September), tapering off only as light drops in autumn.
What strength of feed for rex begonia?
Half strength every feed is the sweet spot for rex begonia: frequent enough to fuel fast growth, dilute enough that it never scorches even when you feed often.
What does over-feeding rex begonia look like?
Brown, scorched leaf tips and margins despite correct watering. A white salt crust on the soil or around the pot edge. Sudden leaf yellowing and drop shortly after a strong feed. Soft, weak, over-stretched growth that cannot support itself. The mistake here is the opposite of most houseplants: under-feeding a fast tropical in peak season starves it, leaving small, pale new leaves and slow growth — but full-strength doses still burn it, so feed often and weak, not occasionally and strong.
Should I flush the soil of rex begonia?
Because you feed often, salts accumulate faster — flush the pot of rex begonia with plain water until it drains freely roughly every month through the feeding season to keep the root zone clean.
Keep reading
- Rex begonia care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water rex begonia — the watering schedule
- The houseplant fertiliser schedule — feeding through the year
- NPK ratio explained — what the three numbers on the bottle mean
- How to fertilise snake plant
- How to fertilise dracaena
- How to fertilise peperomia
- All 200 fertilising guides in the Growli library