Grassy-leaved sweet flag (Acorus gramineus 'Ogon')

Overview

Acorus gramineus ‘Ogon’, commonly known as Grassy-leaved sweet flag, is a superb marginal aquatic perennial valued for its brightly variegated, grass-like foliage. This dwarf cultivar produces narrow leaf blades striped yellow and green, providing year-round visual interest, especially in consistently moist settings. Its low, clumping habit makes Acorus gramineus ‘Ogon’ an excellent accent or ground cover near water features.

This herbaceous perennial thrives where many traditional garden plants struggle, preferring wet soils or even shallow standing water. While it looks very much like a grass, Grassy-leaved sweet flag belongs to the Acoraceae family, adding sophisticated texture to water gardens, bogs, and rain gardens. Its foliage is sweetly fragrant when bruised, confirming its common name, sweet flag.

With minimal routine care required, Acorus gramineus ‘Ogon’ offers significant aesthetic return, spreading slowly via rhizomes to create dense, low-maintenance mats of color. Gardeners in zones 5 through 9 should ensure consistent soil moisture to maximize the brilliant coloration of this specialized perennial.

Fast Facts

• Plant Family: Acoraceae
• Plant Type: Herbaceous perennial
• Hardiness Zones: USDA Zones 5-9
• Size at Maturity:
  • Height: 0.5-1 ft
  • Spread: 0.5-1 ft
• Bloom Time: June to July
• Bloom Description: Greenish yellow
• Sun Exposure: Full sun to part shade
• Water Needs: Medium to wet
• Maintenance Level: Low

How to Grow

Plant Grassy-leaved sweet flag in spring or fall once the danger of hard frost has passed, ensuring locations are consistently moist to wet. Acorus gramineus ‘Ogon’ performs well in average soils, provided moisture is maintained. For water features, containers submerged 3–4 inches deep work perfectly, keeping the crowns consistently wet.

Watering is the most critical element; never allow the soil around this plant to dry out, as scorched leaf tips are the immediate sign of drought stress. While it tolerates full sun, plants in hot summer climates benefit significantly from afternoon shade or filtered light to prevent foliage scorching, especially in drier regions within its range. Fertilization is generally unnecessary when grown in rich, moist garden settings.

This plant spreads slowly by rhizomes, forming a nice ground cover over time, though it is not considered invasive. In northern Zone 5, ensure plants are well-established in consistently wet soil or protected locations, as hardiness can be unreliable. Spring cleanup involves removing any winter-damaged foliage before new growth emerges.

Landscape Uses

Acorus gramineus ‘Ogon’ excels in specialized landscape niches where consistent moisture is guaranteed. Use it as a brilliant ground cover massed along the edge of ponds, streams, or in rain gardens where it helps stabilize banks and manage runoff. Its bright coloration contrasts beautifully with deep green foliage plants near water.

Do not overlook its potential away from standing water; provided the soil remains moist, this plant is effective in perennial borders, rock gardens, or along foundations. In these drier spots, consider using it as a low-profile accent similar to sun-loving sedges (Carex). It performs well beneath trees where root competition is not severe but moisture remains high.

When pairing plants, look for companions that share a love for wet feet or consistent moisture, such as certain Iris species or moisture-loving ferns. The small stature of Acorus gramineus ‘Ogon’ keeps it from overwhelming smaller aquatic plantings, offering texture without excess height.

Standout Features

Flower Qualities

• Insignificant

Noteworthy Characteristics

Acorus gramineus is commonly called grassy-leaved sweet flag. It is native to wetland areas of China, Japan, Korea, India, Thailand, Myanmar and the Philippines. It is a semi-evergreen, marginal aquatic perennial that features a grass-like tuft of narrow, linear leaf blades (1/4” wide) that fan outward to 6-12” tall. Tiny, insignificant, yellow-green flowers bloom from spring to early summer on lateral, sedge-like flower spikes (spadixes to 2-4” long). Flowers give way to very tiny, reddish, fleshy berries. Tufts will slowly spread over time by rhizomes to form a dense ground cover. Plants thrive in wet soils and are commonly grown in water gardens and boggy areas for foliage accent or ground cover purposes. Although it looks like a grass and its common name suggests a grassy appearance, grassy-leaved sweet flag is not a member of the grass family. Originally it was assigned to the arum family (which includes calla lily and jack-in-the-pulpit), but recently it has been transferred from arum to its own family called Acoraceae. Transfer from the arum family was in part done because plants in the genus Acorus do not have true spathes as are typically found in arum family members. Foliage is sweetly fragrant when bruised (hence the common name of sweet flag).Genus name is the Latin name from the Greek akoron used for Acorus calamus and Iris pseuodacorus.Specific epithet comes from the Latin word meaning grass.Foliage is sweetly fragrant when bruised (hence the common name of sweet flag).’Ogon’ is a dwarf plant which features iris-like tufts of narrow, grass-like, variegated leaf blades (6-12” tall and 1/4” wide) which are striped with yellow and green but primarily appear as yellow.

Tolerances

• Heavy Shade
• Erosion
• Wet Soil

Potential Problems

This plant generally resists serious insect or disease issues, making maintenance low. The primary concern for optimal health and color is moisture management. Scorch will occur rapidly if soils are not kept consistently moist to wet, leading to brown, withered leaf tips. Prevent this by ensuring reliable water sources, especially during hot summers or if Acorus gramineus ‘Ogon’ is planted slightly higher than the water line.

Frequently Asked Questions

What hardiness zones is Grassy-leaved sweet flag suitable for?

Acorus gramineus ‘Ogon’ is hardy in USDA Zones 5 through 9, though reliability in the colder end of Zone 5 requires ensuring consistently saturated soil or winter protection.

How large does Acorus gramineus ‘Ogon’ grow?

This dwarf variety typically reaches heights between 0.5 and 1 foot tall, spreading to a similar width of 0.5 to 1 foot.

What sun exposure does Grassy-leaved sweet flag need?

It performs best in full sun to part shade, though gardeners in hot climates should provide afternoon shade to prevent leaf scorch.

When does Acorus gramineus ‘Ogon’ bloom?

The inconspicuous flowers appear between June and July, noted for being a greenish yellow color.

Conclusion

The striking yellow variegation and robust tolerance for wet environments make Acorus gramineus ‘Ogon’ an indispensable choice for marginal plantings and damp garden corners. By keeping the soil consistently wet, you ensure the best yellow coloration and dense, attractive matting behavior from this Grassy-leaved sweet flag. Ensure your site falls within USDA Zones 5–9 and plan your planting near your pond or stream edge today.

Companion Planting

Since Acorus gramineus ‘Ogon’ thrives in heavy moisture, pairing it with other bog or marginal plants enhances the ecosystem. Consider using plants like Pickerelweed (Pontederia cordata) for vertical contrast or various species of Carex that share similar sun and moisture requirements. These companions help create a naturalized, cohesive edge around water features where the Grassy-leaved sweet flag adds low-growing texture.

Design Ideas for Moist Areas

Utilize this plant as a soft, textural edging material in formal water gardens, breaking up the hard lines of stone or container rims. In naturalized settings, let the rhizomes spread to create a dense, erosion-controlling ground cover along stream banks or drainage swales. The bright, almost golden color of Acorus gramineus ‘Ogon’ catches sunlight beautifully, even in partially shaded woodland margins, serving as a year-round vibrant accent.