Ornamental · Poaceae
Japanese Forest Grass
Hakonechloa macra
Give it shade and steady moisture, and its slender blades spill over a bed's edge like falling water.
Partial shade
Every 3–7 days
USDA 5–9
12–18 in · 30–46 cm
Overview
Japanese forest grass is a shade-loving grass whose slender blades all sweep the same way, laying the clump into a soft, cascading mound. It comes from the wooded mountains of Japan, growing on damp, rocky slopes, and the leaves carry that same loose, flowing arch. Seen up close, each thin blade tapers to a fine point and leans downhill with its neighbors, so the whole clump reads like a small run of green water caught mid-fall.
The mound stays low, holding to 12 to 18 inches (30 to 46 cm) tall, the blades layering over one another in fine, overlapping ribbons. On the gold and variegated forms, the Aureola among them, those ribbons glow bright gold and carry thin green stripes running the length of the leaf. As the season turns, the green types flush red and orange across their blades before the color drains for winter.
The color of the blades tracks the light and the water closely. Kept in rich, evenly moist soil and out of hot afternoon sun, the leaves stay smooth, full, and richly colored. Let the ground dry or the sun beat down and the tips crisp and bleach, so steady moisture is what holds the blades clean and whole.
Care
The short version: partial to dappled shade, soil kept rich and evenly moist, and one cut back in late winter that clears the spent blades. It wants slightly acidic ground, shelter from hot afternoon sun, and time for a slow clump to thicken.
Light
This grass wants partial to dappled shade, which sets it apart from most ornamental grasses. It takes full shade and a little morning sun, but hot afternoon light scorches and bleaches the slender blades. Gold and variegated leaves hold their deepest color in bright shade, not deep gloom.
Water
The soil stays consistently moist, since this moisture lover crisps the moment the ground dries and the blade tips brown. Heat and sun draw water from the leaves faster still. Deep watering through dry spells and a mulch layer keep the blades supple and full.
Soil
It grows in humus-rich, well-drained ground on the slightly acidic side, around a pH of 5.5 to 6.5. Compost worked in feeds the slow roots and holds even moisture at the crown so the blades stay well-colored.
Temperature
The clump is cold-hardy to about -20°F (-29°C) and takes summer warmth up to roughly 84°F (29°C). Heat on its own leaves the blades unmarked; heat with dry soil or strong sun is what burns and browns them.
Humidity
Ordinary garden humidity suits it, so there is no figure to hit. Steady soil moisture matters far more than the air, and it is what keeps the fine blade tips from crisping.
Feeding
It is fed once in spring, with a balanced fertilizer or a compost top-dress worked over the crown. That single seasonal feed keeps the blades dense and well-colored through the year.
Pruning
The spent blades are cut right to the ground in late winter or early spring, before the new shoots break through. The clump dies back fully and shows nothing over winter, so that one clean cut clears the way for fresh foliage.
Repotting
The clump is lifted and divided every 2 to 3 years, or when the center congests and the blades there thin and die out. Reduced vigor and roots heaving the crown are the other signs it is time to split.
Size & spacing
The mound reaches 12 to 18 inches (30 to 46 cm) tall and spreads 18 to 24 inches (46 to 61 cm) wide, the blades arching well past the crown. Give each clump that much room and let the slow grower thicken its ribbons of foliage over a few seasons.
When to plant
This grass follows a seasonal cycle rather than a harvest. It is planted out in spring, cut to the ground in late winter before the fresh blades push up, and it lifts thin, inconspicuous yellow-green flower spikes above the mound in late summer.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Plant: spring
- Harvest: late summer (July to August), inconspicuous yellow-green flower spikes
Hardiness
USDA hardiness zones: 5–9
Temperature: down to -29°C
Troubleshooting
Nearly every problem with Japanese forest grass writes itself across the blades, whether from the wrong light or soil run too dry. Look closely at the leaves, their color and their tips, and match what you see below before the mound loses its clean, arching lines.
A low mound that widens by inches each year
A small mound that pushes out only a little wider each year is showing its slow growth, the plant's natural pace as it thickens its arching clump over several seasons rather than sprawling fast. Dry or thin soil narrows those blades and slows the fill further. Rich, evenly moist ground, a spring layer of compost, and winter mulch over the crowns feed the clump and keep frost from lifting it.
Fix:
- Be patient; it is a slow grower that establishes over several years
- Maintain rich, evenly moist soil and a spring top-dress of compost
- Mulch crowns over winter to prevent frost heaving
Brown, crisped tips and bleached blade edges
Brown, brittle tips and pale, bleached edges along the blades are sun scorch, which sets in when the grass takes too much hot, direct sun or the soil dries out in the heat. The gold and variegated blades burn first, their color washing out under harsh afternoon light. Part to dappled shade, soil kept steadily moist, and a mulch layer over the roots let the blades green up clean and whole again.
Fix:
- Move or site in partial to dappled shade, giving only morning sun in hot climates
- Keep soil consistently moist and mulch to conserve moisture
- Water deeply during heat and drought
Gold blades dimming to flat lime green
When the gold and variegated blades drain to a flat lime green and the mound loosens and flops open, the cause is too much shade. More light, not less, brings the color back. In bright dappled shade or morning sun the blades warm to a deeper gold, their green stripes sharpen, and the clump draws back into a tight arching mound. The plain green forms hold their color even in deep shade, where the bright blades cannot.
Fix:
- Move gold and variegated forms to brighter dappled shade or morning sun for best color
- Accept that color is most vivid in part shade, not deep shade
Ragged holes torn through the slender blades
Ragged, irregular holes torn through the slender blades are the work of slugs, which creep in wherever the shade stays damp. A silvery slime trail across the leaf gives them away, and the chewing worsens after a wet spell. Hand-picking or slug controls, cleared debris, and looser, better-aired clumps clear them out. Beyond the odd slug, nothing serious marks these blades.
Fix:
- Hand-pick slugs or use slug controls
- Reduce excess debris and improve air circulation around clumps
Toxicity
Reassuring for homes with pets and children. Japanese forest grass is not toxic and does not appear on the ASPCA's poison lists, so a bitten blade harms no one. The worst likely to follow is a little mild vomiting, the same as any grass, or some sneezing from grass pollen in people prone to allergies.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
A cat that bites into the thin blades is safe. It might bring a little back up, as grass often prompts, but nothing in the leaf is poisonous.
Dogs None
A dog that mouths the arching foliage takes in no toxins. A blade or two may bring on brief mild vomiting, the plain grass reaction, and nothing worse.
Horses None
Horses cropping the blades are safe; this is a plain, non-toxic grass.
Rabbits None
Rabbits nibbling the slender leaves are safe, since the foliage holds nothing harmful.
Livestock None
Cattle, goats, and sheep that graze the blades are safe, as the grass carries no toxic compounds.
Birds None
Birds are safe among the blades, whether they settle in the mound or pick at the seed heads.
People None
Children and adults are safe handling the leaves. The one exception is grass pollen, which can stir allergies in anyone already sensitive to it.
Not poisonous, but pets that nibble grass foliage may occasionally vomit, and grass pollen can trigger allergies in sensitive individuals.
Varieties
The cultivars split mostly by the color of their blades and how brightly the leaves glow in shade. These are the ones worth knowing by their foliage.
Aureola
Aureola, the 2009 Perennial Plant of the Year, carries gold blades striped with narrow lines of green, holding that color best in part shade.
All Gold
All Gold shows solid bright golden-yellow blades that rise more upright and spiky than the arching Aureola.
Beni Kaze
Beni Kaze, its name meaning red wind, keeps green blades through summer that flush red and gold when fall arrives.
Nicolas
Nicolas, a compact green form, burns to fiery orange and red across its blades in autumn.
How to propagate
More Japanese forest grass comes from splitting an established clump into fresh crowns of blades, a slow but dependable job for spring.
DivisionEasy
Spring, just as new foliage emerges · Slow; clumps need 2 to 3 years between divisions and are slow to fill in
Dividing a clump is the simplest way to make more, and the only sure way to keep the gold and green blade patterns of a cultivar true. Split the clumps in spring, just as the fresh blades push up from the crown. Give the divisions time, since these grasses take 2 to 3 years to thicken back into a full mound. Seed sows too, but the seedlings come up plain and won't carry the parent's blade coloring.
Myths
All ornamental grasses need full sun.
Not this grass. Japanese forest grass is one of the few that prefers shade, and its blades tell the story. Hot, full sun scorches and bleaches them, while partial to dappled shade deepens the color and lets the slender leaves arch into that soft, cascading mound.