Japanese blood grass (Imperata cylindrica 'Rubra')

Overview

Japanese blood grass, Imperata cylindrica ‘Rubra’, is highly valued in ornamental horticulture for its distinctive, fiery foliage contrasting sharply with its green origins. This cultivar provides movement and year-round color, transitioning from summer green tips to deep garnet and burgundy hues as the season progresses, making it a striking focal point. While its parent species, cogongrass, is notorious globally as a dangerous invasive weed, the cultivar Imperata cylindrica ‘Rubra’ is recognized as significantly less aggressive, often spreading slowly and rarely seeding.

This perennial ornamental grass thrives when given adequate sunlight and well-drained soil, offering reliable structure and color in USDA Zones 5 through 9. Gardeners appreciate that this selection tends to remain shorter—often only reaching 1 to 2 feet—and possesses far slower spreading tendencies compared to the wild type. By selecting this specific cultivar, gardeners can safely enjoy the dramatic aesthetic of blood grass without the severe ecological risks associated with the standard green cogongrass.

The visual impact of Imperata cylindrica ‘Rubra’ is maximized when the sun backlights the foliage, enhancing the brilliant red coloration. Use this plant where you need a textural accent that maintains visual interest even when not in bloom. Always confirm local regulations, as the status of ornamental cultivars can vary by region, though ‘Rubra’ is generally sold as a manageable landscape addition.

Fast Facts

• Plant Family: Poaceae
• Plant Type: Ornamental grass
• Hardiness Zones: USDA Zones 5-9
• Size at Maturity:
  • Height: 2-4 ft
  • Spread: 2-4 ft
• Bloom Time: Rarely flowers
• Bloom Description: Rarely flowers
• Sun Exposure: Full sun to part shade
• Water Needs: Medium
• Maintenance Level: Medium

How to Grow

Plant Japanese blood grass in spring after all danger of frost has passed, ensuring the soil is well-drained. While it tolerates dry to moist conditions, excellent drainage is crucial for discouraging root issues. Full sun exposure will encourage the deepest, most vibrant red coloration in the upper blades of the Imperata cylindrica ‘Rubra’ foliage, although it can handle light afternoon shade.

Water moderately, especially when establishing the plant, allowing the soil to dry somewhat between waterings. This cultivar demonstrates good drought tolerance once established, aligning with its medium water needs. Fertilization is rarely necessary, as this plant prefers average to poor soils; overly rich soil can sometimes reduce the intensity of the red pigmentation.

Maintenance for this ornamental grass is relatively simple. Because Imperata cylindrica ‘Rubra’ rarely flowers or produces seed, cleanup is mainly focused on aesthetics. Cut back the previous year’s growth in very early spring before new growth begins to emerge, which keeps the clump tidy. Note that ‘Rubra’ is reportedly much less aggressive and should only be propagated by division, avoiding the issues of aggressive rhizome spread seen in other varieties.

Landscape Uses

The primary suggested use for Imperata cylindrica ‘Rubra’ is as a striking accent or massed planting where its color can truly shine. Although the species can naturalize aggressively, the ‘Rubra’ selection is generally better behaved, making it suitable for controlled borders or grouping. The 2 to 4-foot mature height makes it perfect for the middle or back of perennial borders where it contrasts well against broad-leafed, deep green shrubs.

Consider using Japanese blood grass in containers or patio tubs, which provides complete control over its spread and allows you to place this fiery accent precisely where needed for seasonal impact. When backlit by the morning or afternoon sun, the garnet foliage becomes almost translucent and intensely colored, pairing beautifully with cool-toned structural plants or silvery foliage. Although the species is noted for invasive potential, ensure you check local regulations, as some states prohibit the sale or cultivation of certain cogongrass varieties, even ornamental ones like our feature plant.

Standout Features

Noteworthy Characteristics

Imperata cylindrica, commonly known as cogongrass, is now considered to be one of the ten worst weeds in the world. The cultivar ‘Rubra’ (aka var. Rubra) is a shorter, less invasive horticultural selection that reportedly rarely flowers, does not set seed and lacks the invasive spreading tendencies attributed to the species, typically growing much shorter than a foot-and-a-half tall. The upper part of each blade turns garnet red in summer, with the red color often deepening toward burgundy as the growing season progresses.

Tolerances

• Drought
• Black Walnut
• Air Pollution

Potential Problems

No known serious insect or disease problems typically affect Imperata cylindrica ‘Rubra’. The main concern when growing this grass relates to potential misidentification or reversion; green-leaved species plants are highly invasive and destructive. To manage this risk, purchase labeled ‘Rubra’ stock only from reputable nurseries and monitor for any shoots that revert entirely back to green foliage, removing them immediately.

Frequently Asked Questions

What hardiness zones is Japanese blood grass suitable for?

Japanese blood grass (Imperata cylindrica ‘Rubra’) is best suited for planting in USDA Hardiness Zones 5 through 9.

How large does Japanese blood grass grow?

This ornamental grass typically reaches a mature height between 2 and 4 feet tall, with an equal spread of 2 to 4 feet.

What sun exposure does Imperata cylindrica ‘Rubra’ need?

For optimal performance and the best red coloration, Imperata cylindrica ‘Rubra’ prefers full sun, though it can tolerate partial shade.

When does Japanese blood grass bloom?

This specific cultivar, Japanese blood grass, rarely flowers, making it primarily valued for its foliage display rather than its infrequent bloom history.

Conclusion

The vivid, ever-deepening red foliage ensures that Imperata cylindrica ‘Rubra’ remains a dynamic and irreplaceable textural element in modern landscaping designs. While recognizing the notorious reputation of its invasive relatives, this shorter, less aggressive cultivar provides dependable color contrast. Before adding this stunning Japanese blood grass to your garden, confirm its acceptance in your specific local climate zone and prepare well-draining soil for planting this summer.

Companion Planting

Selecting suitable companions for Japanese blood grass involves choosing plants with similar cultural needs for sun and water while providing aesthetic contrast. Because this grass prefers full sun and medium moisture, pair it with perennials that also tolerate drier spells once established. Consider using lower-growing Sedums or ornamental alliums for contrasting forms at ground level. Foliage contrasts are excellent here; pair the fine texture and bright color of Imperata cylindrica ‘Rubra’ with plants offering large, dark green or blue-toned leaves, such as Hosta (in partial shade areas) or Russian Sage (Perovskia atriplicifolia) in full sun exposures.

Propagation Tips

Since the primary concern with cogongrass is its invasive nature, the desired cultivar, Imperata cylindrica ‘Rubra’, is specifically propagated to limit spread. This selection reportedly does not readily produce viable seed; therefore, the only reliable method for propagation is division. Divide clumps in early spring just as new growth is emerging, or in early fall before dormancy sets in. Dig up the entire clump and carefully use a sharp spade or knife to separate it into smaller sections, ensuring each division has a healthy mass of viable roots and rhizomes attached. Replant the divisions immediately at the same depth as the parent plant.