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Plant care

Common Water Starwort (Pond Water Starwort) care

Callitriche stagnalis

Also called Common Water Starwort, Pond Water Starwort, Common Starwort.

RHS H7USDA 4-9Mildly toxic to petsIndoor Individual stems 10–40 cm (4–16 in) long

Watering rhythm

Medium indirect light (a couple of metres from a window)

Fully submerged or surface-floating — permanent aquatic

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Light

Medium indirect light (a couple of metres from a window)

Soil

Pond silt, sand, or no substrate (free-floating)

Humidity

Aquatic — 100% water immersion

Temp

0°C to 22°C

Pet safety

Mildly toxic to pets

Mature size

Individual stems 10–40 cm (4–16 in) long

Care at a glance

Light

Common Water Starwort wants the spot a few feet back from a sunny window — bright enough to read a paperback at noon, but the sun never falls directly on the leaves. Grows well in moderate to bright light with at least 4–6 hours of natural daylight; in very low-light ponds growth is sparse and plant density thins — choose a location free from heavy overhead shade. A faint hand shadow at midday is the right amount; a sharp dark shadow means it's getting direct sun and probably too much.

Watering

Water common water starwort fully submerged or surface-floating — permanent aquatic. 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. Plant in still or slow-moving water at 15–60 cm (6–24 in) depth; also colonises wet mud and shallow margins — no watering required once established in a pond or stream.

Soil and pot

Common Water Starwort grows best in pond silt, sand, or no substrate (free-floating). Can be anchored in pond silt or sand at the base, or simply weighted with lead strips and left to float freely; plant baskets are not necessary and the plant self-roots naturally into the substrate. 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

Common Water Starwort sits happiest at around Aquatic — 100% water immersion humidity and 0°C to 22°C (32°F to 72°F). An entirely aquatic species requiring permanent water contact; when grown in a pond no humidity management is needed, but in an indoor aquarium maintain water temperature between 10–20°C (50–68°F). If you keep the room above 0°C to 22°C 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 common water starwort sparingly. No supplemental fertilisation required; absorbs nutrients directly from the water column, and in nutrient-rich ponds can grow vigorously enough to need periodic thinning. 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 common water starwort in the Growli community. Each is annotated with the most common cause so you know where to start.

  • Overgrowth and Pond Coverage — In nutrient-rich water C. stagnalis grows very rapidly and can cover a pond surface completely, reducing light to other aquatic plants — thin regularly by raking out excess growth in summer.
  • Blanketweed Invasion — Filamentous algae (blanketweed) frequently entangles starwort stems, particularly in warm, sunny water with high nitrate levels; use a pond twirl stick to remove algae and consider barley straw extract to reduce nutrient load.

Propagation

Propagate by stem cuttings 10–15 cm long taken at any time during the growing season; simply push bundles into pond silt or weight and drop into water — they root freely without any additional treatment. 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

Common Water Starwort is mildly toxic to pets. Callitriche stagnalis is not listed on the ASPCA Toxic and Non-Toxic Plant database and no toxic principles have been identified for this species. As pet-safe status cannot be confirmed by ASPCA, it is classified as mildly toxic as a precaution; aquatic access by pets is generally low, but consult a vet if ingestion occurs. 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.

Common Water Starwort care — frequently asked questions

What is the common name for Callitriche stagnalis?

Callitriche stagnalis is most commonly called Common Water Starwort, but it is also known as Common Water Starwort, Pond Water Starwort, Common Starwort. The names refer to the same species, so care instructions for Common Water Starwort apply identically to anything sold as Pond Water Starwort.

How much light does common water starwort need?

Common Water Starwort grows best in medium indirect light (a couple of metres from a window). Grows well in moderate to bright light with at least 4–6 hours of natural daylight; in very low-light ponds growth is sparse and plant density thins — choose a location free from heavy overhead shade.

How often should I water common water starwort?

Water common water starwort fully submerged or surface-floating — permanent aquatic. Plant in still or slow-moving water at 15–60 cm (6–24 in) depth; also colonises wet mud and shallow margins — no watering required once established in a pond or stream. 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 common water starwort toxic to cats and dogs?

Common Water Starwort is mildly toxic to pets. Callitriche stagnalis is not listed on the ASPCA Toxic and Non-Toxic Plant database and no toxic principles have been identified for this species. As pet-safe status cannot be confirmed by ASPCA, it is classified as mildly toxic as a precaution; aquatic access by pets is generally low, but consult a vet if ingestion occurs.

What USDA hardiness zone does common water starwort grow in?

Common Water Starwort is rated for USDA zone 4-9 and RHS hardiness H7. Outside that range, grow it as a container plant that overwinters indoors before the first hard frost.

Common Water Starwort deep-dive guides

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

Featured in these plant shortlists

Common Water Starwort qualifies for 4 curated Growli shortlists — each one filtered objectively from our structured plant-care library, so the selection is consistent and checkable:

Related guides

Common Water Starwort is also known as Common Water Starwort, Pond Water Starwort, and Common Starwort.