Ornamental · Poaceae
Japanese Forest Grass
Hakonechloa macra
Give it shade and steady moisture, and this grass pours over the edge of a bed like water finding its way down.
Partial shade
Every 3–7 days
USDA 5–9
12–18 in · 30–46 cm
Overview
Japanese forest grass is the shade garden's quiet luxury, a grass that turns away from sun and toward the cool, dim corners other plants avoid. It carries the mood of its native home, the wooded mountains of Japan, into a border, softening hard edges with a cascading mound that spills where you place it. Set a run of it along a shaded walk and the whole planting seems to move, like green water drawn downhill.
Its low, unhurried habit is part of the appeal, holding to 12 to 18 inches (30 to 46 cm) and settling naturally at a path's edge or the front of a shady bed. The gold and variegated forms, the beloved Aureola chief among them, lend a lit-from-within warmth to spots that otherwise read flat and dark. Green types close the season in fiery red and orange before they rest for winter.
As a design partner it asks for little once placed with care. Keep the soil rich and evenly moist, spare it the hot afternoon sun, and it holds its poise season after season. The only demand it makes is on your patience, since a young clump takes a few years to settle into the picture you imagined.
Care
The short version: partial to dappled shade, soil kept rich and evenly moist, and one cut back in late winter. Give it slightly acidic ground, shelter from hot afternoon sun, and time for a slow clump to fill its place.
Light
This grass belongs in partial to dappled shade, the exposure that sets it apart from most ornamental grasses. It accepts full shade and a little morning sun, but hot afternoon light scorches the blades and spoils the effect. Gold and variegated forms glow best in bright shade, not deep gloom.
Water
Keep the soil consistently moist, since this is a moisture lover that scorches the moment the ground dries. Heat and sun only deepen its thirst. Water well through dry spells and lay mulch to hold that moisture around the roots.
Soil
Give it 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 helps the soil stay evenly damp without turning heavy.
Temperature
It weathers cold beautifully, hardy to about -20°F (-29°C), and takes summer warmth to roughly 84°F (29°C). Heat alone is no trouble; it is heat paired with dry soil or strong sun that burns the leaves.
Humidity
Ordinary garden air suits it, so there is no figure to chase. Even soil moisture counts for far more than humidity, and it is what keeps the foliage from crisping at the tips.
Feeding
Feed once in spring with a balanced fertilizer, or simply top-dress the crown with compost or organic matter. That single seasonal feed keeps a clump handsome and growing.
Pruning
Cut the old foliage to the ground in late winter or early spring, before the new shoots appear. The plant dies back fully and offers nothing over winter, so that one clean cut a year is the whole of its upkeep.
Repotting
Lift and divide a clump every 2 to 3 years, or when the center congests and begins to die out. Reduced vigor and roots heaving the crown are the other signals that it is time to split and replant.
Size & spacing
Plants reach 12 to 18 inches (30 to 46 cm) tall and spread 18 to 24 inches (46 to 61 cm) wide. Allow each clump that much room and let the slow grower ease into the space over a few seasons.
When to plant
This grass keeps a calm seasonal rhythm rather than a harvest. Set it out in spring, cut the old foliage to the ground in late winter before the new shoots rise, and look for its understated yellow-green flower spikes 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
Most of what troubles Japanese forest grass comes down to the wrong light or soil that has run too dry, and the clump wears its condition plainly. Read what the leaves show, match it below, and adjust the setting or the watering before the look of the planting slips.
A composed clump that fills its corner slowly
A clump that barely widens each year is simply showing its slow growth, the unhurried pace that gives this grass its quiet composure rather than a rush to cover ground. Dry or thin soil holds it back further. Let the design mature at its own tempo: keep the ground rich and evenly moist, top-dress with compost in spring, and mulch the crowns through winter so frost cannot heave them.
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
Scorched tips that dull the clump's soft look
Those browning, crisped edges 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 forms, the very ones prized for their glow, burn first under harsh afternoon light. Settle the clump into part or dappled shade, keep the soil steadily moist, and lay mulch to hold that moisture, and the graceful look returns.
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 dimming to an everyday lime green
When the gold and variegated forms lose their glow and slump open instead of mounding, the culprit is too much shade, which flattens the very color that lifts a dim corner. The remedy is more light, not less. Give colored cultivars a spot in bright dappled shade or morning sun, where the gold reads warm again and the clump settles into a tidy shape. Leave the deepest shade to the green forms, which never asked to shine.
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 interrupting the smooth blades
Ragged holes punched through the blades usually mean slugs, drawn to the damp, shady setting this grass thrives in. Their calling cards are irregular holes and slime trails, worse after a wet spell. Lift the slugs by hand or set out controls, tidy away the debris where they shelter, and open the clumps so air moves through. Past the odd slug, the plant stays untroubled by serious pests.
Fix:
- Hand-pick slugs or use slug controls
- Reduce excess debris and improve air circulation around clumps
Toxicity
A calm note for homes with pets and children. Japanese forest grass is not toxic and stays off the ASPCA's poison lists, so a nibble of the blades harms no one. At most you might see a little mild vomiting, the same as with any grass, or a touch of sneezing from grass pollen in those prone to allergies.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
A cat may share the garden with it in comfort. A blade or two chewed might come back up, as any grass can cause, yet nothing in the plant is poisonous.
Dogs None
A dog wandering the border is in no danger, since nothing here is toxic. A mouthful of leaves brings only the odd bout of mild vomiting, the everyday grass reaction.
Horses None
Grazing horses have nothing to fear from this plain, non-toxic grass.
Rabbits None
Rabbits may pass among it freely, as the foliage holds nothing harmful should they nibble.
Livestock None
Cattle, goats, and sheep meet no risk here, the grass carrying no toxic compounds.
Birds None
Birds are perfectly safe, whether they nestle in the blades or take the seed heads.
People None
Children and adults are safe around it. The single caveat is grass pollen, which can rouse allergies in anyone already sensitive.
Not poisonous, but pets that nibble grass foliage may occasionally vomit, and grass pollen can trigger allergies in sensitive individuals.
Varieties
A small, well-chosen group of cultivars carries this grass, set apart mostly by leaf color and how warmly they light a shaded corner. These are the ones worth designing around.
Aureola
The 2009 Perennial Plant of the Year, Aureola draws the eye with gold leaves striped in narrow green, at their finest under part shade.
All Gold
All Gold offers solid bright golden-yellow blades in a more upright, spiky posture than the arching Aureola.
Beni Kaze
Beni Kaze, whose name means red wind, wears green blades that warm to red and gold once fall arrives.
Nicolas
Nicolas, a compact green selection, closes the season in fiery orange and red.
How to propagate
More Japanese forest grass comes from splitting an established clump, a slow but dependable task suited to spring.
DivisionEasy
Spring, just as new foliage emerges · Slow; clumps need 2 to 3 years between divisions and are slow to fill in
Dividing an established clump is the graceful way to gather more, and the surest way to carry a cultivar's color from one part of the garden to the next. Split the clumps in spring as the new foliage emerges. Give the work time, since these grasses take 2 to 3 years to knit back together between divisions. Seed is an option too, though seedlings will not repeat the parent's coloring.
Myths
All ornamental grasses need full sun.
Not so here. Japanese forest grass is one of the rare grasses that favors shade, a gift for the shady beds most grasses shun. Hot, full sun scorches it, while partial to dappled shade coaxes out its richest color and the soft, cascading form that makes it such a design piece.