Canna 'Roi Humbert' (Red King Humbert) care

Light

Canna 'Roi Humbert' needs sun on the leaves, not just bright ambient room light. Needs at least 6 hours of full sun daily for the best flowering and richest foliage colour. In partial shade, stems stretch and bloom count drops noticeably. A south or west-facing windowsill in the northern hemisphere is the default; anywhere else, expect the plant to stretch and pale out within a season.

Watering

Water canna 'roi humbert' keep soil consistently moist, watering every 2-3 days in warm weather or whenever the top 2-3 cm dries out. The actual day count varies with pot size, light, and season — the finger test (or lifting the pot to feel its weight) is more reliable than a fixed calendar. Empty any drainage saucer afterwards so the pot isn't sitting in water. Cannas are thirsty plants in full growth. Avoid waterlogging at the crown, but never allow the root zone to dry completely during the growing season. Reduce watering sharply once foliage dies back in autumn.

Soil and pot

Canna 'Roi Humbert' grows best in rich, moisture-retentive loam with good drainage. Incorporate plenty of well-rotted organic matter before planting. A pH of 6.0-7.0 suits them well. Heavy clay should be improved with grit and compost to prevent rhizome rot. A pot with a working drainage hole is non-negotiable for this species — even free-draining mix will turn soggy in a closed planter. If you love the look of a decorative pot without a hole, use it as a cachepot around an inner nursery pot you can lift out to water.

Humidity and temperature

Canna 'Roi Humbert' sits happiest at around 40-70% humidity and 18-30°C (64-86°F). Tolerates average garden humidity. In hot, dry climates a thick mulch layer helps retain moisture and maintain cooler root temperatures. If you keep the room above 18 year-round and avoid placing the plant near a cold draught, a hot radiator, or an air-conditioning vent, you have already handled the two biggest indoor stressors.

Fertilising

Feed canna 'roi humbert' sparingly. 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. Skip fertiliser entirely on a stressed, recently-repotted, or actively wilting plant — fertiliser salts make damage worse, not better. Wait for a round of healthy new growth before resuming a feeding rhythm.

Common problems

Below are the issues we see most often on canna 'roi humbert' in the Growli community. Each is annotated with the most common cause so you know where to start.

• Canna leaf roller — Caterpillars roll and chew young leaves. Inspect regularly and remove by hand; use Bt (Bacillus thuringiensis) for heavier infestations.
• Rust (Puccinia thaliae) — Orange-brown pustules on leaf undersides in warm, humid weather. Remove affected leaves promptly and improve air circulation.
• Rhizome rot — Caused by waterlogged soil, especially over winter. Ensure good drainage and store lifted rhizomes in dry, frost-free conditions.
• Slugs and snails — Feed on emerging shoots in spring. Use iron phosphate pellets or copper barriers; check under mulch regularly.
• Viruses (Bean yellow mosaic) — Causes streaked, mottled foliage. Transmitted by aphids — control aphids early and remove and destroy affected plants.

Companion plants

Canna 'Roi Humbert' pairs well with Dahlia, Elephant ear (Colocasia), Salvia, and Verbena bonariensis. These are species with similar light and water needs, so you can group them in the same room or on the same shelf and water as a batch.

Propagation

Divide rhizomes in spring once the risk of frost has passed, ensuring each section has at least one growing point or 'eye'. Pot up divisions in moist compost and keep warm (above 15°C) until roots are established before planting out. Propagation is the cheapest, most satisfying way to expand a collection — and it doubles as insurance against losing a mature plant to an accident. Take a backup cutting once the parent is established and healthy.

Toxicity to pets

Canna 'Roi Humbert' is mildly toxic to pets. Canna species are not individually listed by the ASPCA, but the genus is generally regarded as having low toxicity. Ingestion may cause mild gastrointestinal upset in dogs or cats; keep pets away from rhizomes as a precaution. If you keep cats, dogs, or curious children in the house, weigh placement carefully — a high shelf or a hanging planter is enough for casual safety. For severe ingestion incidents, call your local vet and the ASPCA Animal Poison Control Center (in the US, 888-426-4435).

Pet-safety status is sourced from the ASPCA Toxic and Non-Toxic Plant List, which catalogues the most-asked-about plants for cats, dogs, and horses.

Canna 'Roi Humbert' deep-dive guides

Every aspect of canna 'roi humbert' care, each with its own calibrated guide:

• Common canna 'roi humbert' problems & fixes
• Canna 'Roi Humbert' watering schedule
• Canna 'Roi Humbert' light requirements
• Best soil mix for canna 'roi humbert'
• Canna 'Roi Humbert' fertilizing guide
• When to repot canna 'roi humbert'
• How to propagate canna 'roi humbert'
• How to prune canna 'roi humbert'
• What's eating my canna 'roi humbert'?
• Canna 'Roi Humbert' growth rate & size
• Canna 'Roi Humbert' cold hardiness
• Canna 'Roi Humbert' temperature & humidity
• Is canna 'roi humbert' toxic to cats & dogs?
• Is canna 'roi humbert' toxic to cats?
• Is canna 'roi humbert' toxic to dogs?
• All 20 Canna varieties
• Getting canna 'roi humbert' to bloom

Featured in these plant shortlists

Canna 'Roi Humbert' qualifies for 3 curated Growli shortlists — each one filtered objectively from our structured plant-care library, so the selection is consistent and checkable:

• Best drought-tolerant houseplants — Houseplants that prefer to dry out — forgiving of forgotten watering and ideal for travel or busy weeks.
• Best flowering houseplants — Indoor plants grown for their blooms — selected from the flowering species in Growli’s plant-care library.
• Best houseplants for full sun — Houseplants that want direct sun — the species for a hot south or west-facing windowsill where shade-lovers scorch.
• Browse all 30 plant shortlists — pet-safe, low-light, drought-tolerant and more

Related guides

Canna 'Roi Humbert' is also commonly called Red King Humbert or King Humbert Canna.

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