Fertilising guide
How to fertilise Canna 'Roi Humbert' (Canna 'Roi Humbert')— schedule & NPK
Also called Red King Humbert, King Humbert Canna.
More about canna 'roi humbert'
About Canna 'Roi Humbert'
Canna 'Roi Humbert' · also called Red King Humbert, King Humbert Canna · flowering
Canna 'Roi Humbert' (also sold as Red King Humbert) is a bold, tall canna lily cultivar bearing scarlet-red flowers above bronze-purple foliage. It thrives in full sun with consistently moist, fertile soil. Plants die back in winter in cooler climates; rhizomes must be lifted and stored frost-free. Mildly toxic to pets.
Growth habit: Upright rhizomatous perennial
Watch for — Slugs and snails: Feed on emerging shoots in spring. Use iron phosphate pellets or copper barriers; check under mulch regularly.
What fertiliser canna 'roi humbert' actually wants — and why
Canna 'Roi Humbert' 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 canna 'roi humbert': 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 canna 'roi humbert', 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 canna 'roi humbert':
Apply a balanced slow-release fertiliser (e.g. 10-10-10) at planting, then switch to a high-potassium liquid feed every 2-3 weeks from midsummer to encourage flowering. Stop feeding once growth slows in autumn. Treat that as every 2-3 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 canna 'roi humbert' 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 canna 'roi humbert'
Half strength is the safe default for canna 'roi humbert' — 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 canna 'roi humbert' first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the canna 'roi humbert' watering schedule.
Signs you are over-feeding canna 'roi humbert'
Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for canna 'roi humbert':
- 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 canna 'roi humbert'
- 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 canna 'roi humbert' care brief covers soil, humidity and the common problems for this species.
Flushing and leaching the salts
Flush the pot of canna 'roi humbert' 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 canna 'roi humbert'
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 canna 'roi humbert' — frequently asked questions
What fertiliser does canna 'roi humbert' 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. Canna 'Roi Humbert' 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 canna 'roi humbert'?
Apply a balanced slow-release fertiliser (e.g. 10-10-10) at planting, then switch to a high-potassium liquid feed every 2-3 weeks from midsummer to encourage flowering. Stop feeding once growth slows in autumn. Apply a balanced slow-release fertiliser (e.g. 10-10-10) at planting, then switch to a high-potassium liquid feed every 2-3 weeks from midsummer to encourage flowering. Stop feeding once growth slows in autumn. Treat that as every 2-3 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 canna 'roi humbert'?
Half strength is the safe default for canna 'roi humbert' — houseplant feeds are formulated strong, and the diluted dose is gentler on the roots while still ample for foliage.
What does over-feeding canna 'roi humbert' 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 canna 'roi humbert' 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 canna 'roi humbert'?
Flush the pot of canna 'roi humbert' 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
- Canna 'Roi Humbert' care — the full brief (light, soil, humidity, problems, pet safety)
- How often to water canna 'roi humbert' — the watering schedule
- The houseplant fertiliser schedule — feeding through the year
- NPK ratio explained — what the three numbers on the bottle mean
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- All 11687 fertilising guides in the Growli library