Pōhinahina (Vitex rotundifolia) – My friend is your enemy.
Today, the ecological buzz-term among school-age kids is invasive species. Unfortunately, despite this education, the term is still confused or synonymized with introduced or naturalized. For the record, an invasive species is defined as an organism (plant, animal, fungus, or bacterium) that is not native (i.e., introduced by humans) and has negative effects on our economy, our environment, or our health. Not all non-native species in Hawai‘i are invasive. For example, plumeria were first introduced to Hawai‘i in 1860 by Wilhelm Hillebrand and are native to the Caribbean, Mexico, South America, and throughout Central America. Here, the trees rarely produce seed and none of our native plant communities are in danger of being invaded and overcome by plumeria. Another common human tendency is to apply moral values to biological classifications. For example, native or Hawaiian plants and animals are “good” while alien or invasive organisms are “bad.” Of course, the reality is that nature is neither good nor bad, it just is. Most fascinating is that whether or not a species is invasive or not is not totally determined by the characteristics of the species itself but also by the environment it is placed in; a species can be invasive in some places and quite benign in others. Pōhinahina is a good example of this. Here in Hawai‘i, pōhinahina is a rather well-behaved species, sharing its wild coastal habitat with other native and non-native plants. (Only in cultivation does pōhinahina become unnaturally aggressive in Hawai‘i.) Not so in North and South Carolina where pōhinahina was introduced to control beach erosion and then went crazy. Today, Carolinians are spending millions of dollars each year to eradicate pōhinahina from miles and miles of coastal dune ecosystems where it threatens native species such as the sea beach amaranth and, possibly, even sea turtles.
Habitat & Appearance: Pōhinahina is a coastal creeping shrub naturally (i.e., native) common on sandy beaches and dunes from Korea south to Australia and India east to Hawai‘i. Pōhinahina leaves are silvery (because of the many white hairs) grayish-green and generally simple and oval, although you may discover an occasional palmate compound leaf. Clusters of small purple flowers periodically emerge from the stem-tips. These develop into small green round fruits that ripen to a dark brown or black.
(Top to Bottom) Florida on the lookout. Nearly-ripe fruits. Seedlings. Propagation via horizontal stem-cuttings. A forest of seedlings or horizontal stem-cuttings?
Pōhinahina in Hawaiian Culture: Pōhina means “to fall prone” or “topple” which is indeed the way pōhinahina grows. According to Nagata (1970), Hawaiians once used pōhinahina medicinally. Today (and, perhaps, in the past) the fragrant leaves of pōhinahina are sometimes used in lei.
Collecting Seeds: In cultivation, pōhinahina flowers and fruits repeatedly throughout the year. Collect the corky fruits when they are dark brown or black (a bit darker than those photographed here) and easily removed from the plant. Clean the outside of the fruits well under running water in a wire strainer to remove the outer skin along with any bacteria and fungal spores. Pōhinahina fruits have a stony endocarp making it very difficult to extract the seeds without damage, therefore, don’t even try. The seeds will germinate just fine if you sow the entire cleaned endocarp.
Growing from Seed: Almost no one grows pōhinahina from seed because cuttings are so much easier and quicker. I found no difference in germination between freshly-cleaned fruits and those soaked one week in water (changed daily) before sowing; in both treatments, the seeds sprouted in 6 - 8 weeks. After sprouting, you can hasten seedling growth with fertilizer, either controlled-release or low-dose liquid. It takes 3 - 6 months for the seedlings to grow 8 - 10 inches tall; they are then ready to plant in your garden.
Growing from Cuttings: You can use either Method One or Method Two to root pōhinahina cuttings. In fact, pōhinahina roots so readily that landscapers often just push cut stems vertically into the ground and then water daily for two to three weeks to create a pōhinahina feature. My favorite method is to use horizontal stem-cuttings because the resulting plant looks like a tiny forest of pōhinahina seedlings. If you wish to try, collect hardwood or semi-hardwood stem-cuttings and remove all the leaves. Further cut the stems so each has three or more nodes and fits nicely in a pot with any type of clean media. Place two or more cuttings horizontally atop the media (see photograph) and then cover them with another half-inch of media (or simply bury the stems horizontally in the existing media). Water the pot once or twice daily to make sure the surface media and stem cuttings do not dry out. In two to three weeks you’ll discover tiny shoots (from the buried nodes) emerging from the media. After you see several shoots, begin treating them as you would a pot full of seedlings; water and fertilize regularly to promote rapid growth.
Growth in the Garden: Today, pōhinahina is extremely popular with commercial landscapers in Hawai‘i because: (1) it is an attractive plant with its silvery leaves and numerous purple flowers, (2) it is very easily propagated from stem-cuttings, (3) it grows well under cultivation in many unnatural environments such as clay soils and non-coastal areas, (4) it tolerates extreme pruning. In the garden, you can let your pōhinahina grow in its natural pōhina form or prune it into a manmade shape such as a hedge; the plant will grow well regardless. For the most silvery leaves and maximum flowering, keep your pōhinahina in full sun and water it very little (e.g., once a month).
Diseases & Pests: It’s likely the strong fragrance of pōhinahina leaves keeps most pests away. The only problem I’ve consistently noticed is spittlebugs. These do little harm but are unsightly. Get rid of the bugs with a strong spray of water or contact pesticide such as malathion.
Ā ā Ē ē Ī ī Ō ō Ū ū