Growli
Let's go

Fertilising guide

How to fertilise Cathedral Begonia (Begonia 'Cathedral')— schedule & NPK

Also called Cathedral begonia, Cathedral Windows begonia.

More about cathedral begonia

About Cathedral Begonia

Begonia 'Cathedral' · also called Cathedral begonia, Cathedral Windows begonia · houseplant

Begonia 'Cathedral' is a compact rhizomatous begonia introduced around 1966, prized for its deeply ruffled and contorted dark olive-green leaves with red undersides and chartreuse highlights that create a stained-glass window effect. It thrives in bright to medium indirect light, prefers bottom-watering to avoid crown rot, and rewards consistent warmth and moderate humidity. Plants remain compact, reaching 30-45 cm, and produce masses of small deep-pink flowers on tall spikes in late winter and spring. Toxic to cats and dogs.

Growth habit: Compact rhizomatous perennial

What fertiliser cathedral begonia actually wants — and why

Cathedral 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 cathedral 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 cathedral 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 cathedral begonia:

Feed with a quarter-strength balanced or high-potassium liquid fertiliser every 3-4 weeks during the growing season; omit in winter. 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 cathedral 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 cathedral begonia

Half strength every feed is the sweet spot for cathedral 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 cathedral begonia first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the cathedral begonia watering schedule.

Signs you are over-feeding cathedral begonia

Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for cathedral begonia:

Signs you are under-feeding cathedral begonia

If the symptoms point at watering, light or roots rather than nutrition, the full cathedral 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 cathedral 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 cathedral 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 cathedral begonia — frequently asked questions

What fertiliser does cathedral 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. Cathedral 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 cathedral begonia?

Feed with a quarter-strength balanced or high-potassium liquid fertiliser every 3-4 weeks during the growing season; omit in winter. Feed with a quarter-strength balanced or high-potassium liquid fertiliser every 3-4 weeks during the growing season; omit in winter. 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 cathedral begonia?

Half strength every feed is the sweet spot for cathedral begonia: frequent enough to fuel fast growth, dilute enough that it never scorches even when you feed often.

What does over-feeding cathedral 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 cathedral begonia?

Because you feed often, salts accumulate faster — flush the pot of cathedral begonia with plain water until it drains freely roughly every month through the feeding season to keep the root zone clean.

Keep reading