Water Starwort Facts, Care, Benefits, & Hardiness (Callitriche palustris)
Water starwort, also known as vernal water starwort or common waterwort, belongs to Callitrichaceae, the water starwort family. Its Latin name is derived from the Greek words carlos and trichos, which translate to “beautiful hair,” as this plant’s stems and leaves have a soft, hair-like appearance. The majority of the leaves float in small clusters atop the water’s surface, with the entire plant growing up to a foot in height, roots relatively firmly planted in the soil.
It’s native to North America, Europe, and the majority of Asia, typically growing in and around the slow-moving, shallow waters of creeks, small lakes, and vernal ponds where it helps provide valuable habitat to frogs, turtles, and other reptiles and amphibians that depend upon vernal pools for survival. While not technically a native species in Australia, palustris has been there long enough that it’s become naturalized and is not considered an invasive issue.
Benefits & Uses of Water Starwort (Common Waterwort)
The small, ample leaves hold fish eggs and young quite well while also disguising them from potential predators. It can be confused for the very similar-looking pond water starwort (Callitriche stagnalis), which is invasive in many parts of the United States. Though not particularly palatable to humans, waterfowl such as ducks enjoy eating the leaves and berries, the latter of which ripen in the autumn.
Water Starwort Growth, Hardiness & Climate
As a vernal plant, water starwort grows very quickly once spring hits, reaching its maximum height often in only a couple of weeks, before most other plants have fully leafed out. Native to a variety of regions around the world, water starwort is considered to be relatively hardy. It stops growing vertically once it reaches the surface of the water, focusing on producing small rosettes of floating leaves and tiny green flowers that are pollinated primarily by water or wind rather than by insects or birds.
The small leaf clusters only spread to approximately 1.5 centimeters across, Full sun works best for this plant, but it can tolerate partial shade for a couple of hours a day. Full shade will kill most water starworts. Temperature climates are best, but they can persist most anywhere so long as temperatures don’t fall below 20° F (-6° C) for longer than a week or two, or exceed around 80° F (26° C) for too long.
How to Plant Water Starwort In Ponds
If purchased from a store or transplanted as an adult plant, you can plant water starwort directly into the silt at the bottom of the pond in as deep as 18 inches of water, though around 6 to 12 inches is best. For younger or less established plants, an aquatic basket can be used until the roots become more robust and are able to hold the plant into the soil.
Another method is to weight the plant to the bottom of the pond utilizing small planting weights or gently placing a portion of the roots beneath a small rock that’s just large enough to hold the plant down. If using planting weights, please avoid lead-based weights, as these are toxic and inevitably the lead will leach into the water where it can bioaccumulate in fish, birds, and even plants, causing a host of potential health issues. A very adaptable plant, sand, clay, loam, and silt all work well for palustris.
How to Care For & Maintain Water Starwort
A plant that requires minimum maintenance, palustris shouldn’t require much care at all beyond planting it in full to partial sun in fairly shallow water. It’s not particularly prolific and shouldn’t spread out of control, but if it’s growing a bit too much you can trim the leaves, pull up a few plants, or simply allow herbivorous fish to feed on the leaves. Once the plant(s) die back in the fall, you’ll need to remove any dead matter from the pond to maintain healthy water quality. Seeds can be allowed to drop to the pond bottom or harvested and planted later.
How to Winter Water Starwort
Water starworts will die off in the autumn, typically dropping seeds that will sink into the sediment at the water’s bottom. These seeds will remain dormant over winter and germinate on their own once the water thaws out. If you would like to, you can also transfer the plant to an indoor tank before it dies off in the autumn, though this is not necessary as it should drop self-germinating seeds.
Is Water Starwort Toxic, Poisonous or Invasive?
Water starwort is not toxic to fish or wildlife, nor is it considered invasive in any portion of North America, Europe, or Asia. Since it doesn’t occur naturally in South America, you likely should not try to acquire or propagate this plant if you live in that region. As mentioned above, palustris is not technically a native species in Australia but has become naturalized as it’s not a plant that easily overtakes areas.
Is Water Starwort Edible? Will Fish Eat it?
Your fish, koi in particular, are likely to munch on it as the leaves are soft and easy to consume. If they’re eating the plants too much, you can move the starwort to a shallow shelf that the fish can’t easily swim to. Also make certain that you’re feeding your fish quality food that is tasty and provides all the nutrition that they need so that they’re less likely to feed on your plants.
Where to Buy Water Starwort? (UK & US)
Not an uncommon plant, water starwort can be purchased from most aquarium and pond retailers, either in store or online. You should never remove a plant from the wild, as ecosystems are delicate and could be disturbed if any species are removed. Palustris in particular is an excellent oxygenator that also provides habitat for a variety of fish and semi-aquatic species such as salamanders, and thus is valuable to water ecosystems and should not be removed from natural areas.