Overview of Fiber Optic Grass
Fiber optic grass is an unusual plant (which is technically a rush and not a true grass, so another common name is low bullrush) that most people acquire because of its unique appearance. Isolepis cernua (= Scirpus cernuus), in the sedge family (Cyperaceae), is a variable evergreen species with a mop-like tuft of fine green stems. It is found in wet places, growing as a marginal water plant or in sandy or peaty areas near the sea in its native range of western and southern Europe, the British Isles, North Africa, the west coast of North America (California to British Columbia and Alaska), Australia, and New Zealand.
This bright green, grass-like plant has small flower spikes at the stem tips, giving it a look reminiscent of a fiber optic lamp, hence the common name.
These easy-to-grow plants grow upright as a young plant and then gracefully droop as they mature. The 10 to 12 inch tall clumps of fine, glossy, hair-like leaves can reach a spread of 20 inches at maturity. The foliage may yellow as temperatures drop in fall or turn brown if the plant doesn’t receive enough moisture.
Tiny flowers are produced on the tip of each leaf. The cone-shaped terminal inflorescences begin a white or silver color, but eventually turn tan or brown. The plants will bloom year-round.
General Care of Fiber Optic Grass
I. cernua is a tender perennial (zones 8a to 11b) generally grown as an annual in cold climates but it can be kept as a houseplant in a sunny window or greenhouse over the winter. Bring it indoors before freezing temperatures occur and set the pot in a shallow tray of water.
Fiber optic grass grows best in full sun with plenty of moisture. Do not allow it to dry out or the foliage will turn brown. It can be planted in containers, in the ground, or kept in a water garden or pond. It will tolerate some shade but will become lankier under those conditions.
Landscape Use of Fiber Optic Grass
Grow these plants as specimens to show their unique character, or plant as accents among other plants grown for foliage or flowers. Combine it with other moisture-loving annuals in boxes or pots, or grow it in its own container in a grouping of potted plants. Try it as an underplanting with dark-leaved elephant ears (Colocasia esculenta ‘Black Magic’ or other cultivars). Place it on the edge of borders or beds, or between rocks at water’s edge drooping over or into the water.
For a novelty conversation piece, use it to top a “head” container! The fine texture of this plant is a good contrast to plants with coarse leaves, and its mounded habit is a good foil for upright plants and spiky flowers. Fiber optic grass is a good addition to container water gardens.
When using this plant in a water garden, gradually increase the water level it sits in unless you purchased it from an aquatic plants display. This allows the roots to become accustomed to being submerged. In a water garden, it combines well with horsetails (Equisetum), dwarf papyrus, and canna (but it is best to keep each in separate pots). It can be planted on the water’s edge or in the shallows of ponds, positioned so that the water level is no more than 2 inches above the soil. The leaves trailing in the water will provide shelter for frogs and fish.
If plants become overly tall or lanky, cutting the leaves back promotes rapid regrowth. Plants can be cut back to a few inches after division in spring, to promote new growth. Avoid shearing in winter when the plant is not growing, however. This plant has few pest problems and is resistant to deer. Mealybugs may infest it indoors if not submerged in water.
Propagating Fiber Optic Grass
I. cernua is easy to grow from seed, and it will readily self seed under the right conditions, but it can also be propagated vegetatively. Divide plants that are full size or those that have outgrown a container. Just chop it into pieces and replant. It is best to do this only in spring if the plants are to be overwintered outdoors.
Cultivars of Fiber Optic Grass
There are a few cultivars available. They are:
- ‘Iggy’ has a dense, compact habit and grows just 10 inches tall. It flowers the first year from seed.
- ‘Live Wire’ (part of the PanAmerican Seed® ColorGrass® collection) is seed propagated, with a very compact habit, growing just 6 to 8 inches tall and 18 to 20 inches wide.
Author: Susan Mahr, University of Wisconsin-Madison
Reviewers: Allen R. Pyle, Horticulture Outreach Specialist, UW-Madison Extension, Bruce Spangenberg, Horticulture Outreach Specialist, UW-Madison Extension
Revised: June 2026
