Canna 'Black Knight' (Black Knight Canna Lily) care

Light

Aim for at least 4-6 hours of direct sun on the leaves. Performs best in full sun (minimum 6 hours). The dark, near-black leaf pigmentation develops most intensely under strong sunlight; shade dilutes the colour and reduces flowering. If your only bright window faces south, that's perfect for canna 'black knight' — same window any aroid would fry on.

Watering

Watering canna 'black knight': keep evenly moist throughout the growing season, watering every 2-4 days depending on temperature. The number that matters isn't the day of the week — it's how dry the top 2-3 cm of the pot feels. A finger in the soil tells you more than a watering app. After every watering, tip the saucer. Do not allow the root zone to dry out completely in summer. In containers, check daily in hot weather as pots dry fast. Reduce to occasional watering after the first frost kills the top growth.

Soil and pot

Canna 'Black Knight' grows best in rich, moisture-retentive loam amended with organic matter. Dig in generous compost before planting. 'Black Knight' is a heavy feeder and benefits from a deep, well-prepared bed. Avoid compacted or waterlogged soils that cause 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 'Black Knight' sits happiest at around 40-65% humidity and 15-30°C (59-86°F). Tolerates typical outdoor humidity in temperate summers. Mulching reduces soil moisture loss and maintains a more stable root environment. If you keep the room above 15 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 'black knight' sparingly. Apply a balanced granular fertiliser at planting time, then feed with a liquid tomato or high-potassium feed every 2-3 weeks once buds begin to form to intensify flower colour. 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 'black knight' in the Growli community. Each is annotated with the most common cause so you know where to start.

• Canna leaf roller — Larvae roll leaves and feed within, leaving untidy brown edges. Remove by hand or apply Bt to young caterpillars.
• Rust — Orange pustules appear on leaf undersides in humid conditions. Remove affected foliage and avoid overhead watering.
• Botrytis (grey mould) — Can attack stored rhizomes in damp conditions. Allow cut surfaces to dry for 24 hours before storage and keep stored material in barely moist vermiculite.
• Virus (mosaic) — Mottled or streaked leaves signal viral infection carried by aphids. Remove and destroy infected plants to prevent spread.
• Slugs — Particularly damaging to emerging shoots. Use iron phosphate bait in spring as shoots push through the soil.

Companion plants

Canna 'Black Knight' pairs well with Canna 'Durban', Dahlia 'Bishop of Llandaff', Ricinus communis, and Salvia guaranitica. 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 with a clean, sharp knife, leaving at least one bud per section. Dust cuts with sulphur powder or cinnamon to reduce rot risk, then pot into moist compost at 18°C or higher. 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 'Black Knight' is mildly toxic to pets. Not individually listed by the ASPCA. Canna genus plants are considered low toxicity overall, but ingestion may cause mild gastrointestinal irritation in cats and dogs; keep rhizomes out of reach of pets. 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 'Black Knight' deep-dive guides

Every aspect of canna 'black knight' care, each with its own calibrated guide:

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

Featured in these plant shortlists

Canna 'Black Knight' qualifies for 4 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.
• Best fast-growing houseplants — Houseplants documented as fast or vigorous growers — quick to fill a pot, cover a pole or trail down a shelf.
• Browse all 30 plant shortlists — pet-safe, low-light, drought-tolerant and more

Related guides

Canna 'Black Knight' is also commonly called Black Knight Canna Lily.

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