Fertilising guide
How to fertilise Rex Begonia (Begonia rex-cultorum)— schedule & NPK
Also called rex begonia, painted-leaf begonia, fancy-leaf begonia.
More about rex begonia
About Rex Begonia
Begonia rex-cultorum · also called rex begonia, painted-leaf begonia · houseplant
Rex begonias are rhizomatous foliage begonias grown for spectacular leaves swirled in silver, burgundy, pink, green, and purple. Flowers are insignificant; the show is all in the foliage. They demand high humidity, bright indirect light, and careful watering, rewarding attentive growers with some of the most dramatic leaf patterns of any houseplant.
Growth habit: Rhizomatous, mounding foliage plant; a creeping surface rhizome sends up successive showy leaves rather than tall stems. Spreads outward to fill its pot. Tiny pink flowers may appear but are often removed to direct energy into foliage. Some cultivars go semi-dormant in winter, losing leaves before reflushing.
Watch for — Crispy brown leaf edges: Usually humidity too low or salt buildup. Raise ambient humidity, keep away from heating vents, and flush the soil to clear accumulated fertiliser salts.
What fertiliser rex begonia actually wants — and why
Rex Begonia is an easy, light foliage feeder — a half-strength balanced liquid feed through the growing months keeps it green without forcing weak, sappy growth.
A balanced general houseplant feed (roughly even N-P-K) is exactly right — it is grown for foliage, so steady, moderate nitrogen for healthy leaves is the goal, not a bloom or root 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:
Feed every 2-4 weeks during spring and summer with a balanced houseplant fertiliser diluted to half strength. Rex begonias are sensitive to fertiliser salts, so weak and frequent beats strong and occasional. Stop feeding in autumn and winter when growth slows. Flush the soil occasionally to prevent salt buildup at the rhizome. Treat that as every 2-4 weeks between spring through early autumn (roughly March to September); ease off in autumn and stop entirely in the low light of winter.
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 is the safe default for rex begonia — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
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, crispy leaf tips and edges with no sign of underwatering.
- A white, crusty salt deposit on the soil surface or pot rim.
- Weak, pale, stretched new growth that flops.
- Lower leaves yellow and drop while the soil is correctly watered.
Signs you are under-feeding rex begonia
- Uniformly pale or yellow-green leaves, oldest first.
- Noticeably small new leaves and stalled growth in good light and season.
- A generally tired, lacklustre look despite correct watering and light.
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
Flush the pot of rex begonia with plain water until it runs freely from the base every couple of months in the feeding season — it washes out the fertiliser salts that cause brown tips.
Organic vs synthetic feeds for rex begonia
Organic options
A diluted seaweed or worm-casting feed, or fish emulsion if you can tolerate the smell indoors. UK: Westland or Baby Bio Organic, dilute seaweed; US: Espoma Indoor! or Neptune's Harvest fish & seaweed. Slow, gentle and hard to overdo.
Synthetic / liquid feeds
A general-purpose houseplant liquid at half strength — UK: Baby Bio, Westland Houseplant Feed or Phostrogen; US: Miracle-Gro Indoor Plant Food or Schultz. Convenient and fast-acting; the only risk is overdoing it.
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 general houseplant feed (roughly even N-P-K) is exactly right — it is grown for foliage, so steady, moderate nitrogen for healthy leaves is the goal, not a bloom or root formula. Rex Begonia is an easy, light foliage feeder — a half-strength balanced liquid feed through the growing months keeps it green without forcing weak, sappy growth.
How often should I feed rex begonia?
Feed every 2-4 weeks during spring and summer with a balanced houseplant fertiliser diluted to half strength. Rex begonias are sensitive to fertiliser salts, so weak and frequent beats strong and occasional. Stop feeding in autumn and winter when growth slows. Flush the soil occasionally to prevent salt buildup at the rhizome. Feed every 2-4 weeks during spring and summer with a balanced houseplant fertiliser diluted to half strength. Rex begonias are sensitive to fertiliser salts, so weak and frequent beats strong and occasional. Stop feeding in autumn and winter when growth slows. Flush the soil occasionally to prevent salt buildup at the rhizome. Treat that as every 2-4 weeks between spring through early autumn (roughly March to September); ease off in autumn and stop entirely in the low light of winter.
What strength of feed for rex begonia?
Half strength is the safe default for rex begonia — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
What does over-feeding rex begonia look like?
Brown, crispy leaf tips and edges with no sign of underwatering. A white, crusty salt deposit on the soil surface or pot rim. Weak, pale, stretched new growth that flops. Lower leaves yellow and drop while the soil is correctly watered. Feeding rex begonia year-round on a fixed schedule, including dark winter months, is the most common mistake — it cannot use the nutrients in low light and the surplus simply burns the roots and crusts the soil.
Should I flush the soil of rex begonia?
Flush the pot of rex begonia with plain water until it runs freely from the base every couple of months in the feeding season — it washes out the fertiliser salts that cause brown tips.
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 2464 fertilising guides in the Growli library