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Plant care

Water Canna (Aquatic Canna) care

Canna glauca

Also called Aquatic Canna, Louisiana Canna, Aquatic Indian Shot.

RHS H2USDA 7-12Mildly toxic to petsIndoor 1-2 m tall

Watering rhythm

Direct sun (at least 4-6 hours)

Aquatic marginal — roots in 0-30 cm of standing water

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Light

Direct sun (at least 4-6 hours)

Soil

Heavy loam or aquatic substrate

Humidity

50-80%

Temp

18-32°C

Pet safety

Mildly toxic to pets

Mature size

1-2 m tall

Care at a glance

Light

Water Canna needs sun on the leaves, not just bright ambient room light. Requires full sun for best growth and flowering. Position at the sunniest part of the pond margin. Plants in partial shade produce fewer flowers and weaker stems. 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 water canna aquatic marginal — roots in 0-30 cm of standing water. 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. Unlike terrestrial cannas, Canna glauca tolerates roots in up to 30 cm of standing water. Plant at the pond margin in shallow water or permanently waterlogged soil. Grows vigorously in warm, moist conditions.

Soil and pot

Water Canna grows best in heavy loam or aquatic substrate. Plant rhizomes in large aquatic planting baskets filled with heavy loam-based compost or directly into a waterlogged pond bed. Ensure good nutrient availability — this is a vigorous, fast-growing plant. 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

Water Canna sits happiest at around 50-80% humidity and 18-32°C (64-90°F). Originates in tropical wetlands and prefers warm, humid conditions. Outdoor pond environments naturally provide adequate humidity during the growing season. 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 water canna sparingly. Apply aquatic fertiliser tablets to the planting basket in spring and repeat in midsummer. Water Canna is a strong grower and benefits from consistent nutrition through the growing season. 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 water canna in the Growli community. Each is annotated with the most common cause so you know where to start.

  • Canna leaf roller caterpillar — Larvae roll and web the young leaves. Unroll affected leaves and remove caterpillars by hand, or use a biological spray (Bacillus thuringiensis).
  • Rhizome rot in cold water — Cold or waterlogged soil below 10°C encourages rot. Lift and store rhizomes frost-free if overwintering in zones 7-8.
  • Aphids on flower buds — Colonies cluster around emerging buds. Use insecticidal soap or a strong water jet to control them.
  • Spider mites in dry summers — Pale mottling on leaves indicates mite activity. Increase moisture and humidity around the plant; treat with miticide if severe.
  • Failure to flower — Insufficient sun or overcrowded rhizomes prevent flowering. Divide every 2-3 years and ensure a sunny, open position.

Companion plants

Water Canna pairs well with Thalia geniculata, Pontederia crassipes, and Nymphaea colorata. 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 temperatures exceed 15°C. Each section should have at least one growing bud. Pot into large containers of loam-based compost and keep warm and moist until new growth is established before moving to the pond margin. 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

Water Canna is mildly toxic to pets. The ASPCA lists Canna generalis (Canna lily) as mildly toxic to cats and dogs, potentially causing mild gastrointestinal signs if ingested. Canna glauca is the same genus and is treated as having the same toxicity profile. 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.

Water Canna care — frequently asked questions

What is the common name for Canna glauca?

Canna glauca is most commonly called Water Canna, but it is also known as Aquatic Canna, Louisiana Canna, Aquatic Indian Shot. The names refer to the same species, so care instructions for Water Canna apply identically to anything sold as Aquatic Canna.

How much light does water canna need?

Water Canna grows best in direct sun (at least 4-6 hours). Requires full sun for best growth and flowering. Position at the sunniest part of the pond margin. Plants in partial shade produce fewer flowers and weaker stems.

How often should I water water canna?

Water water canna aquatic marginal — roots in 0-30 cm of standing water. Unlike terrestrial cannas, Canna glauca tolerates roots in up to 30 cm of standing water. Plant at the pond margin in shallow water or permanently waterlogged soil. Grows vigorously in warm, moist conditions. The finger-test (or lifting the pot to feel its weight) beats a fixed weekly calendar because pot size, light, and season all change how fast the soil dries.

Is water canna toxic to cats and dogs?

Water Canna is mildly toxic to pets. The ASPCA lists Canna generalis (Canna lily) as mildly toxic to cats and dogs, potentially causing mild gastrointestinal signs if ingested. Canna glauca is the same genus and is treated as having the same toxicity profile.

What USDA hardiness zone does water canna grow in?

Water Canna is rated for USDA zone 7-12 and RHS hardiness H2. Outside that range, grow it as a container plant that overwinters indoors before the first hard frost.

Water Canna deep-dive guides

Every aspect of water canna care, each with its own calibrated guide:

Featured in these plant shortlists

Water Canna qualifies for 2 curated Growli shortlists — each one filtered objectively from our structured plant-care library, so the selection is consistent and checkable:

Related guides

Water Canna is also known as Aquatic Canna, Louisiana Canna, and Aquatic Indian Shot.