How to Plant & Grow Star Grass in Ponds (Rhynchospora colorata)

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how to plant star grass in ponds
Star grass grows best in warm regions, in or near water. T.Voekler / CC BY-SA

Star grass – also known as white-top sedge, starrush whitetop, and white star sedge – is a rather unique species of sedge belonging to Cyperaceae, the sedge family. Some confusion can occur when searching for this plant, as it used to belong to the genus Dichromena (the star grasses) from its discovery in the 1700s until the 1980’s, when Dichromena was merged into the genus Rhynchospora (the beak sedges).

It’s often still referred to as Dichromena due to its difference in appearance from most other species in Rhynchospora. For simplicity’s sake, it can be considered a sub-genus within the beak sedge genus.

Members of the genus Rhynchospora can be found on every continent except Antarctica, but are particularly common in the southern hemisphere. Star grass is native to the southeastern United States, from Texas to Virginia, but it can be found in portions of Mexico and South America. There are some reports of it in southern Africa and Australia, likely escapees from cultivation. Star grass is at times confused with swamp whitetop sedge (Rhynchospora latifolia), but the latter is significantly taller with larger bracts than star grass.

Facts, Benefits & Uses of Star Grass

benefits of star grass rhynchospora colorata
The white bracts of star grass draw in pollinators, while the seeds provide food for wildlife.
Judy Gallagher / CC BY

So, what makes star grass so unique? Unlike most other sedges that are wind-pollinated, star grass has white, star-shaped bracts that resemble flowers, which draw in a variety of pollinators like bees and butterflies. That means that this species has an ecological advantage in that it can be pollinated by both wind and native pollinating insects and birds.

Sedges are like the grasses of wetland ecosystems (though that simple of a comparison is a disservice to both plant types), and provide an amazing array of ecosystem benefits. They provide food and shelter via their leaves, shoots, tubers, and seeds for a large variety of animals and insects, while their fibrous, rhizomatous roots are excellent at holding riverbanks in place, preventing erosion, and filtering pollutants out of water. Their overall importance to proper ecosystem functioning cannot possibly be overstated, and star grass is no exception to this.

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Star Grass Fact Sheet:
Evergreen Aquatic Perennial
USDA 7 – 11
Full sun to partial shade
White, yellow
June – August (Summer)
Height & spread 30–61 cm (12–24 in)
5 – 15 cm (2 – 6 in)
pH 5.0 – 7.0

Star Grass Growth, Hardiness & Climate

growth and hardiness of star grass
Star grass forms large clumps that can spread, and may need to be cut back seasonally. Elke Freese / CC BY-SA

Star grass is relatively fast growing, able to reach its full size of two feet tall with a two foot spread (per plant) in a single season, usually within 3 to 4 months. Some plants can achieve heights closer to three feet, but somewhere between one and two feet is most common. Their roots are rhizomes, and are able to spread rather proficiently – you’ll need to separate this plant by clumps as needed to help control its growth.

What appear to be its “flowers” are actually just white bracts, which are modified leaves that resemble flowers but are much less expensive to make. These surround the actual flowers, which are quite small and inconspicuous, that bloom yellow from June through August. These large and obvious bracts help draw in pollinators to the flowers that would otherwise potentially go unnoticed by pollinators. In more subtropical climates, growth and blooming can occur year round.

Like with all sedges, white star sedge is a wetland plant that is typically only found in moist or saturated habitats, either along the edges of rivers, ponds, and the like or in wetlands. They are somewhat tolerant of cooler temperatures, but do best in the warmer hardiness zones of 7 through 11, in full or at least partial sunlight, with ample access to moisture.

How to Plant Star Grass In Ponds

aquatic plants bog plants for ponds
Dick Culbert from Gibsons, B.C., Canada / CC BY

Immature star grass plugs should be planted in approximately two inches of moist soil or water, while mature plants can be planted in six inches of damp earth or water. They are able to grow in both soil as well as marginally in standing water, but if planted in standing water do place some substrate like small rocks or gravel gently about the base to help hold the roots in while the plant establishes itself in the new habitat. Space each plant at least two feet apart to allow for growth.

How to Care For Star Grass

how to care for star grass
Judy Gallagher / CC BY

White star sedge is largely a self-sustaining plant, provided it has enough water and nutrients. Planting it marginally along the moist edge or just inside of the shallows of your pond will ensure both of these things, particularly if you have fish that add to the nutrient content of the water via waste.

As their roots are able to spread easily, you may consider planting star grass in pots or planting baskets to help control their spread. Otherwise, divide the clumps, rootball and all, and either dispose of what you don’t want (never just throw them on the ground or into a natural environment, as they may establish there) or plant them elsewhere around your garden pond. Another option is to cut off any excess growth in the winter while the plants are dormant – this will reduce stress to them, and result in improved spring growth.

As always, be sure to clean any trimmed or dropped foliage from your pond to encourage healthy water quality.

How to Winter Star Grass

Star grass is able to survive winters within its native hardiness zones (7-11) by simply dying down to its roots, going dormant, and resprouting from these roots as well as dropped seeds the following spring.

In more northern climes, dropped seeds may persist beneath snow and ice but the sedges themselves are likely to die completely. Some hardy individuals may survive provided temperatures do not drop too harshly. If you live in a northern region, keep in mind, first and foremost, that star grass is not native to your area. If it’s legal to have, each spring you can either purchase new star grass or you can collect the beak-shaped seeds from each plant and simply plant them early in the spring.

Is Star Grass Toxic, Poisonous or Invasive?

As mentioned above, star grass is primarily native to the southeastern United States, as well as portions of Mexico and South America. That means that if you live in the UK, Australia, India, and so on, star grass is technically invasive in your area. If you’re quite stuck on having sedge in your garden, you should first research native varieties to your region. The hyperlinks here will take you to a list of sedges native to the UK, Australia, India, Canada, and the US. They are not comprehensive, but a start. For the US one, you’ll need to type “sedge” into the search bar and set your location to see a list of native species.

If there are no native sedge species for your region, or none that suit your needs, next you must check if it’s legal to have star grass where you live. Finally, if it’s not banned, do not plant it in natural areas (only in your pond or water garden), and then plant it in pots or baskets so that it’s less likely to escape into nature. Properly dispose of any cuttings or dropped seeds in the trash or a well-enclosed compost bin.

Star grass is not known to be toxic to humans, domesticated animals, or wildlife, and is in fact eaten by a variety of wildlife including insects, ducks and other waterfowl, sparrows, turkeys, muskrats, and rabbits, to name a few. The seeds are of particular wildlife value.

Is Star Grass Edible? Will Fish Eat it?

Star grass is edible. Your fish are unlikely to eat it, but in the event that they show interest in any of the dropped seeds, this should not be harmful to them. Nonetheless, clean any dropped or trimmed foliage out of your pond on a regular basis to maintain healthy water quality.

Where to Buy Star Grass & Seeds? (UK & US)

In the US, star grass and similar sedges can be purchased from many plant nurseries. Elsewhere, it’s easiest to find from online retailers. Some nurseries or aquatics stores may be able to special order it in for you.

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