Flower, buds, fruit, and the habit of nīoi. Eugenia koolauensis is related to the non-native Surinam cherry (Eugenia uniflora), sometimes intentionally planted, but often unintentionally found in landscapes, usually spread by fruit-loving birds, such as bulbuls (Pycnonotus spp.). Healthy leaves and those with leaves infected with ʻōhiʻa rust (Austropuccinia psidii).

Growth Requirements

General

    Nīoi is a beautiful native shrub or small tree that is underutilized in the urban Hawaiian landscape, but can sometimes be challenging to grow. However, most issues arise from neglecting pests (e.g., black twig borers) and fungal problems (e.g., ʻōhiʻa rust). Nīoi is very susceptible to these pests! Therefore, rapt attention to both of these must be given for this beautiful native to grow successfully.

    Although nīoi is drought-tolerant, it does appreciate some moisture. But, excessive watering can lead to ʻōhiʻa rust (Austropuccinia psidii), a bright yellow fungal rust that appears on the leaves and fruit, as well as any exposed fruits from insect or bird activity. While it can tolerate partial sun, nīoi prefers full sun to produce abundant flowers and fruits.

    Nīoi is an excellent choice as a showcase or accent shrub, or hedge similar to Mock orange (Murraya panculata) due to its potential to be easily trimmed. However, since nīoi are still rare in cultivation, it is not yet known if anyone has tested it to see whether it can be trimmed lightly or as aggressively as mock orange. Its versatility and beauty make it a valuable addition to any Hawaiian landscape.

    For potted plants, using organic or natural fertilizers at a low dose of around ¼ the recommended strength, once or twice a month is ideal. Once planted in the ground, nīoi generally does not require additional fertilizers. 

    The best way to grow nīoi is from seed. Nīoi starts flowering and fruiting, sometimes with seeds, when around 2 feet (0.6 m) tall. As the shrubs mature, it will produce fruits and will have up to four (rarely five) seeds, while smaller shrubs will typically have one, sometimes two seeds, per fruit. Under optimal conditions of sunlight, water, air circulation, and fertilizer, it can reach a substantial size of over a foot within a year. When collecting seeds from nīoi, it is important to note that they can be unpredictable when it comes to blooming and fruiting. Some years, you may see an abundance of flowers and fruits, while other years may yield very little or none at all. I (Eickhoff) have found it is best to plant seeds fresh or shortly thereafter, as they do not store well even in a refrigerator.

    Birds introduced to Hawaiʻi, such as Red-vented and Red-whiskered bulbuls (Pycnonotus cafer, P. jocosus), are particularly fond of nīoi fruit and so closely monitor the ripening fruits. If you are planning to collect nīoi seeds, it is essential to protect the fruits from these birds. Bird netting is an effective method, but it is crucial to regularly check for any trapped birds.

    Interestingly, I (Eickhoff) have often observed that bulbuls will eat the fruit on the spot while sitting on a branch. A bulbul will peck at each fruit, then drop the seeds. Therefore, keep an eye out for clean tannish-white or gray pea-sized seeds in the debris or open ground beneath the shrub. These are usually just as viable as those directly collected from the shrubs.

Pests and Diseases

     To control ʻōhiʻa rust (Puccinia psidii), frequent applications of a combination of systemic insecticide (e.g., imidacloprid) with a suitable fungicide. Black twig borers are a major pest and can quickly destroy small nīoi if not treated as soon as detected or preferably before with a regular maintenance program, especially in the wetter months of the year. It is also good to alternate between applications or change the fungicides, perhaps yearly. Refer to the Pests & Diseases page for further details. 

Special Features and Information

General

     Eugenia koolauensis is a member of the Myrtle family or Myrtaceae [Nature Clearly], which boasts a staggering number of over 5,950 species worldwide [Christenhusz 2016]. Among the native Myrtaceae members are the indigenous nīoi (Eugenia reinwardtiana), ʻōhiʻa hā (Syzygium sandwicensis), and five endemic species of Metrosideros: Lehua ʻāhihi or ʻāhihi (M. tremuloides), lehua papa (M. rugosa), and three known by the name ʻōhiʻa (M. polymorpha, M. macropus, and M. waialealae) [Wagner et al. 1990].

    Non-native relatives, many of which have naturalized in Hawaiʻi, are abundant and include myrtle, tea tree, strawberry guava or waiawī ʻulaʻula, pineapple guava or kuawa, allspice, eucalyptus, melaleuca or paper bark, bottlebrush (Callistemon spp.), and Surinam cherry (Eugenia uniflora), among others. Unfortunately, some of these species have become seriously invasive, displacing large areas of native forests with a single species-dominated landscape. A prime example of this is the highly aggressive strawberry guava (Psidium cattleianum), under which little vegetation can thrive due to its dense canopy.

Hawaiian Name

    The "Hawaiian" or bird chile pepper (Capsicum frutescens) also goes by the name nīoi or nīoi pepa [Hawaiian Dictionaries].

Etymology

    The generic name, Eugenia, is named for Prince Eugene (1663-1736) of Savoy, France [Wagner et al. 1990]. The specific epithet, koolauensis, refers to the Koʻolau Mountains on Oʻahu. The addition of -ensis indicates origin or place [Gledhill 2008].