Japanese forest grass is normally planted as a container-grown nursery plant in spring, though it can also be planted when it turns cool in the fall. Just make sure not to plant it during summer’s dry heat. It can take a full year to reach its full size, and then will spread slowly in a manner that doesn’t require much in the way of control. Spreading mulch over the ground around the plants will help keep the soil cool and retain moisture during summer, and also will keep weeds at bay. In the northern end of the hardiness range, heaping mulch over the mounds may help prevent winter kill—gardeners in zone 4 can successfully grow this plant by protecting it in this way for the winter. Leaves may scorch in hot weather, and the plant mounds can sometimes heave upward under the effect of freezing winters. There are virtually no serious pest or disease issues with Japanese forest grass.
Light
Japanese forest grass prefers partial shade, such as that found in woodland areas. In cooler climates, it can tolerate more sun, while in warmer regions it can tolerate near full shade. Part-shade conditions typically produce the brightest yellow in the leaf color; full shade may make the leaves more green than variegated, and full sun can scorch the leaf tips.
Soil
Japanese forest grass does well when planted in any moist, well-drained soil with a good amount of humus and other organic matter. Dense soils should be amended with compost or peat moss before planting.
Water
Japanese forest grass requires frequent watering and moist soil. This is not a plant for arid conditions, though established plants can tolerate short periods of drought without catastrophe. Most gardens find that the standard 1 inch, divided into two or three equal waterings per week, is ideal for this plant. A good amount of water-retentive organic material in the soil helps Japanese forest grass enjoy the moisture it requires.
Temperature and Humidity
Where Japanese forest grass is native, it thrives in cool, moist conditions. But if you give it shade, water it regularly, and keep its roots cool by mulching, it can do well in warmer areas. Extreme heat or cold may kill the plant. It is reliably hardy up to zone 5, but it can be quite successful in zone 4 if mulched in the winter.
Fertilizer
Organic mulch provides all the nutrition this plant needs. If you do fertilize, do it in spring just after the first new growth appears, using a balanced fertilizer, then omit any feeding for the rest of the season.
Types of Japanese Forest Grass
The pure species form of H. macra has bright green leaves that form a mounding cascade 12 to 18 inches high. A number of good cultivars are also available that offer some variety in leaf color and size:
Hakonechloa macra ‘Aureola’: This beautiful variegated form has chartreuse and green leaves that form an elegant mounding cascade 12 to 18 inches tall.H. macra ‘Albostriata’: The green leaves on this cultivar have thick and thin creamy white stripes. The plant is more sun-tolerant than the golden forms, and it grows faster and taller, to as much as 36 inches. It may also be more cold-hardy than the other cultivars.H. macra ‘All Gold’: This cultivar has brighter leaves and is comparatively upright and spiky in form. The overall plant is smaller and grows slower than the other cultivars.H. macra ‘Benikaze’: With a name translated as “red wind,” this cultivar is green through the summer but takes on varying shades of red as the weather cools off.H. macra ‘Alboaurea’: This cultivar has leaves with long stripes of creamy white, yellow, and bright green.H. macra ‘Naomi’: This yellow and green variegated cultivar turns a striking purplish-red in fall.H. macra ‘Nicolas’: This unusual cultivar has brilliant green foliage that turns striking shades of red, yellow, and orange in fall before dying back for winter.
Pruning
No pruning is necessary for these plants, other than removing dead leaves as they turn yellow and brown. At the end of the growing season, it’s a good idea to cut back and remove the dead foliage before mulching for the winter. However, in colder regions, the foliage is often left in place until spring to help insulate the crown.
Propagating Japanese Forest Grass
Named cultivars do not produce viable seeds, so most forms of Japanese forest grass are propagated by division. Here’s how to do it:
How to Grow Japanese Forest Grass From Seed
While named cultivars generally do not produce viable seeds, the pure species form of H. macra can sometimes be propagated by harvesting seeds from the dried flowers and planting them in small containers filled with potting mix. Seeds will take a year or two to develop into viable plants, so it is much more common to propagate by division (see above).
Potting and Repotting Japanese Forest Grass
This ornamental grass can also be grown in containers, where it cascades down over the edge for a nice softening effect. Choose a large pot (any material) that has drainage holes to prevent the soil from becoming boggy, and place the pot in a shady spot that receives some dappled light. Other than that, growing the forest grass in a container is quite easy. Like any potted plant, it will need more frequent watering—daily, in hot conditions. And potted specimens may benefit from a monthly feeding with diluted fertilizer, as frequent watering tends to leach out soil nutrients. This slow-growing plant will not outgrow its container for many years, if ever. In colder regions, the pots should be moved to a sheltered location (a garage, porch, or cold frame) to go dormant for the winter. Or, the pots can be buried in the garden up to the rim to spend the winter.
Overwintering
Japanese forest grass should generally be cut back to near ground level as the foliage dies back as winter approaches. In colder climates, a thick layer of dry mulch heaped over the crowns will help protect the plant from freeze-thaw cycles that can kill the plant. Zone 4 gardeners can usually avoid winter kill by mulching the plant.
How to Get Japanese Forest Grass to Bloom
In mid- to late summer, tiny flowers appear as small inflorescences, but they are nondescript and often go unnoticed. Thus, there is no particular reason to worry if this plant does not flower.
Common Problems With Japanese Forest Grass
This plant is nearly immune to serious pest and disease problems, but you may find that winter frost causes the plant crowns to heave up from the ground. Applying a thick layer of mulch over the crowns as winter sets in can help prevent this. If it does occur, it is an easy matter to replant the clumps at the proper depth as new growth begins in spring. Japanese forest grass can develop scorched, brown leaves if the plant is growing in sunny conditions or in an especially hot climate. This is rarely a serious problem; keep the plant well-watered and prune off dead leaves.
