Puʻukaʻa inflorescences with nearly-ripe fruits (achenes). A trio of young plants along a stream on O‘ahu, likely sprouting from the escaped seeds of mature plants in a restoration planting upstream in Waimea Valley. Puʻukaʻa does just fine in a container (Photograph courtesy of Forest & Kim Starr CC BY 3.0 US.). 

Growth Requirements

General

    Cyperus trachysanthos looks great in the ground, a container, a pond, or other water feature. Consider creating a miniature native Hawaiian wetland using a large container or an in-the-ground flexible pond-liner (see Marsilea villosa; Growth Requirements for how-to details) that is home to all your native wetland plants (e.g., Bacopa monnieri, Bolboschoenus maritimus, Cyperus javanicus, C. laevigatus, C. trachysanthos, Eleocharis erythropoda, E. obtusa, Marsilea villosa, Schoenoplectus tabernaemontani). On a more practical note, the fibrous roots of puʻukaʻa planted en masse (2 to 4 ft [61 to 122 cm] apart) along a stream or pond bank can control soil erosion. And, in restoration projects, puʻukaʻa is a source of food, nesting material, and shelter for native waterfowl. Lastly, puʻukaʻa is a great alternative to the popular alien umbrella sedge (Cyperus involucratus).

    Place your puʻukaʻa in a site that receives full sunlight for all or most of the day. While puʻukaʻa does not have leaf margins as sharp as many other native sedges, you should still avoid planting it immediately adjacent to a walkway or near places where children play.

    Cyperus trachysanthos is great for freshwater ponds and water features, but it can also be grown in drier soil (or media), provided the soil or media always remains moist, either from rain or watering. Puʻukaʻa can withstand heat, but its leaves tend to dry out and snap, becoming permanently folded if exposed to prolonged strong winds. We have grown puʻukaʻa in clay and organic-dominant soils, and in containers with cinder- or perlite-dominant media.

    Puʻukaʻa grows rather quickly, and you can expect your plant to be nearly full size (about 2 ft [61 cm]) and producing seeds in about a year. Since puʻukaʻa has a reputation as a short-lived perennial, you should collect achenes from your plant early and store them in your refrigerator so you can sprout them later. That is, if it is not already producing replacement seedlings around it.

    If I (Koebele) didn't know that Cyperus trachysanthos was a federally-listed endangered plant, I would have thought it was a common native wetland weed in Hawai‘i based on my experiences growing puʻukaʻa. In the nurseries I've helped manage over the years, I was always pulling out puʻukaʻa seedlings that had sprouted up in the pots of other native Hawaiian plants surrounding this prolific sedge; if I didn't, the puʻukaʻa seedlings quickly overwhelmed the landlord plant, and I was forced to repot it in clean seed-free media.

    If your puʻukaʻa grows slowly or begins to yellow, consider applying a small amount of balanced single-digit fertilizer or spraying your plant with an organic or inorganic water-soluble fertilizer diluted to ¼ to ⅓ recommended strength. Then, wait to see how your plant responds before repeating the treatment. Only apply fertilizer if your plant is in the ground or a container; if it is in a pond or water feature, the fertilizer can pollute the water and cause excessive algal growth. Do not over-fertilize.

    Old seed heads and dead leaves should be pruned away to keep your puʻukaʻa looking tidy. If you want to avoid puʻukaʻa seedlings popping up in the pots of surrounding plants, remove the inflorescences early before they mature. Some growers give their puʻukaʻa a close (2 to 3 inches) "haircut" every one to two years to promote a flush of new growth.

Pests and Diseases

    Above ground, puʻukaʻa is infrequently attacked by aphids, mealybugs, or scale insects, which, in turn, are often farmed and protected by ants. Below the ground or the media in a pot, puʻukaʻa is more frequently attacked by root mealybugs. Look for these by carefully removing the pot from the plant's root mass; infestations appear as hairy/powdery white masses on the roots or in the media. Refer to the Pests & Diseases page for ways to battle the above-mentioned pests. However, if your puʻukaʻa is growing in a pond or water feature with fish or other aquatic fauna, you should remove your plant (hopefully, you kept it in a pot) before treating it with any chemicals such as soaps, oils, etc., that could poison the water and kill your animals. 

Special Features and Information

General

    The large Sedge family (Cyperaceae) has about 5,500 described species in approximately 90 genera [WikipediA;Cyperaceae]. There are currently (2025) fourteen Cyperus species native to Hawai‘i, nine being endemic, while the rest are indigenous. There are also about 25 non-native and naturalized Cyperus species in Hawai‘i [Flora of the Hawaiian Islands]. Some of the better-known non-native Cyperus species in Hawai‘i are: papyrus (Cyperus papyrus), the source of ancient Egyptian paper and the origin of the English word "paper"; umbrella sedge (Cyperus involucratus), a popular ornamental; and purple nutsedge or "nutgrass" (Cyperus rotundus), a noxious lawn weed that keep homeowners busy and commercial gardeners employed.

Hawaiian Name

    Puʻukaʻa is a Niʻihau name [Wagner et al. 1990] and the one most often used locally; the name kaʻa is rarely used. This name is also used for Cyperus prescottianus (syn. Torulinium odoratum subsp. auriculatum), another rare endemic sedge in Hawai‘i.

Etymology

    The genus name Cyperus comes from kyperos, the Greek word for "sedge" [Wagner et al. 1990]. The species name, trachysanthos, is from the Greek words, trachys, meaning "rough," [Merriam-Webster] and anthos, meaning "flower," [WikipediA] likely a reference to the species' spiky flower clusters.