Growth Requirements
General
Achyranthes sandwicensis, with its silvery foliage and abundant tassel-like flower spikes, is a striking, easy-to-care-for addition to any landscape. Use it as an accent, or, planted 3 to 6 feet (1 to 2 m) apart, as a screen or lightly-pruned hedge. Kuluī can also be kept in a container but will become stunted if not sequentially transferred to a larger and larger pot.
Achyranthes sandwicensis does best in a site with full sunlight for all or most of the day. If planted in the shade, it tends to become leggy and lose its silvery appearance. Once established, provide kuluʻī with infrequent heavy waterings, followed by long dry periods that permit the surface soil to dry out. Obviously, a kuluʻī in a container will need more frequent watering, but you should try to keep it to a minimum; your kuluʻī will "tell" you when it needs water with wilted leaves.
Kuluʻī is tolerant of extreme heat and drought, strong winds, and some salt spray. It will grow in lava/cinder, clay, and organic-dominant soils, provided there is good drainage. We have never tried to grow kuluʻī in sand or coralline soil but suspect it would do okay, at least in coralline soil. If planted in a flat location with clay-dominant soil, we recommend heaping up the soil into a mound or ridge (and perhaps adding some cinders) to improve drainage.
Under optimum conditions, kuluī grows fast and matures quickly. It's not unusual to have a shrub 3 feet (1 m) or more tall and blooming in about a year. However, it has also been our experience that kuluī (in a landscape) slows down its vegetative growth once it starts flowering and fruiting, possibly because it is directing much of its energy and resources toward reproduction.
While not necessary, in-the-ground kuluʻī benefit from biannual applications of a balanced controlled-release fertilizer or foliar feedings in the morning (to prevent burning) every month with an organic or inorganic fertilizer at ¼ to ⅓ the recommended strength. However, avoid over-fertilizing since this can make the shrub more attractive to pests and result in abnormally large and less silvery leaves. Potted kuluʻī should be similarly fertilized.
Occasionally, we have seen signs that look like senescence, such as branches dying for no apparent reason (see photograph above). Obviously, these dead branches should be quickly removed for aesthetics, but also because they may be a symptom of a disease or pest we don't yet know about or understand. We have also observed that regular but modest hand-pruning of an older kuluī will keep it from becoming straggly and stimulate new growth.
Perhaps because cultivated kuluī live under such ideal conditions, they sometimes senesce or "burn out" before their tenth or even fifth birthday. Therefore, collect and store (in a refrigerator) their tiny fruits for future propagation; there's no need to separate the tiny seeds from the single-seeded fruits. Alternatively, propagate a few replacement plants from stem cuttings, which root easily and quickly.
Pests and Diseases
Kuluʻī is infrequently infested by sap-sucking insects like mealybugs and scale insects. Look for these infestations near the stem-tips and on its roots, and refer to the Pests & Diseases page for treatments.
