Growth Requirements
General
Achyranthes sandwicensis, with its silvery foliage and abundant tassel-like inflorescences, is a striking, easy-to-care-for addition to any landscape. Use it as an accent, or, planted three to six 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, wind, as well as some salt spray. It will grow in lava/cinder, clay, and organic-dominate 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 three feet (1 m) or more tall and blooming in about a year. However, it has also been our experience that kuluī (in the 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. Occasionally, we have seen signs that look like senescence, such as branches dying for no apparent reason. 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.
While not necessary, kuluʻī benefit from biannual applications of a balanced (e.g.,13-13-13) controlled-release fertilizer or foliar feedings in the morning (to prevent burning) every month with a water-soluble 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.
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.
