Native Hawaiian Garden (7722) - Hinahina kū kahakai

Hinahina kū kahakai (Heliotropium anomalum) – but I don’t live near the ocean!

One can debate why so many of Hawai‘i’s native coastal plants have made their way into people’s yards and gardens (and, into the commercial landscape market). Perhaps, it’s because many, many more people spend their time along Hawai‘i’s coastlines rather than hiking or camping in Hawai‘i’s inland forests and, therefore, are more familiar with these native plants. Or, maybe, it’s because so many of Hawai‘i’s native coastal plants are very easy to propagate. It could also be because Hawai‘i’s native coastlines are dominated by low-stature herbs and shrubs that are much easier to incorporate into (for most of us) a tiny yard or lānai. Whatever the reason, unfortunately all too often I see these native coastal additions to the home garden or commercial landscape do poorly because the homeowner or landscaper has completely forgotten about the plant’s natural habitat. Should you really be surprised if your hinahina kū kahakai or ‘ākulikuli languishes and is covered with bugs after you plant it under your biggest shade tree and water it every morning along with the rest of your plants? Yes, there are a few native coastal plants such as pōhinahina and naupaka kahakai that will survive or may even do well in very unnatural environments. But, they are the exception, not the rule.

Most of the native coastal plants people want in their gardens naturally live in very sunny dry places with their roots surrounded by well-drained sandy or rocky substrate. If you want your native coastal plant to survive long-term and look like the wild plants you’ve seen down at the beach or in one of those Hawai‘i field guides (And, who doesn’t want a super-silvery hinahina with densely clustered leaves?), you need to mimic that environment. One of the best and easiest ways to do this is to plant your Hawaiian coastal plant in a container. Fill the container with sand, coral rubble and a tiny amount of organic media (nearly any store-bought potting media will do). Alternatively, you can replace all or most of the sand and coral rubble with graded black – not red – cinder. (For best results, use the half-inch graded cinder, not the ungraded stuff that contains everything from two-inch rocks to lava dust.) Place your container with coastal plant in the sunniest spot you have, and stop watering it every time you look at it. Of course, how sunny and dry that spot is, as well as the size of the container, will ultimately determine how often you do need to water your plant. But, in general, once a day is way too much, and once a week is likely closer to the mark.

If you want your native coastal plant in the landscape, not a container, find the sunniest area in your garden and create an elevated mound of sand and coral rubble (or black cinder). This will create a small micro-habitat that will mimic the plant’s natural habitat (i.e., sunny with a well-drained substrate). Do not mix and level the sand and coral into the soil beneath; doing so will eliminate the well-drained micro-habitat you’re trying to create. Lastly, if you really want to create an artificial coastline, mist your plant every so often with some seawater. Not only will this provide some micronutrients to your plant, but it will also help keep some pest bugs away.

Habitat & Appearance: Heliotropium anomalum is widely distributed throughout Polynesia. In Hawai‘i, hinahina kū kahakai is considered an endemic variety referred to as var. argenteum, a reference to its closely appressed silky hairs (a botanical form of sunscreen). According to Wagner et al. (1990), this prostrate subshrub grows wild in coastal sandy areas on Ni‘ihau, Kaua‘i, O‘ahu, Moloka‘i, and rarely on Maui and Hawai‘i. Today, because of restoration and landscape plantings, one is also likely to see hinahina on Kaho‘olawe, Lāna‘i, and some of the Northwest Hawaiian Islands. The plant forms bluish-green silvery mats that cover the sand or grow atop rocky dry coastal sites. The small mostly-white and fragrant flowers are clustered on forked stalks; flowering and fruiting are sporadic, often coming a few weeks after significant rains. The flowers develop into small nutlets with each nutlet usually containing four very small seeds.

Hinahina kū kahakai leaves and flowers. Fruit stalk with mature seeds. Hinahina seedlings. Wild plant on O‘ahu.

Hinahina kū kahakai in Hawaiian Culture: Hawaiians referred to a number of native plants covered with silvery hairs as hinahina including the Hawaiian wormwood (Artemisia), silversword (Argyroxiphium), Hawaiian Geranium and others. Hinahina kū kahakai is further identified as the silvery plant that grows near the ocean (kahakai). Hawaiians used and continue to use hinahina stem-tips with their densely clustered and whorled leaves (with or without the stalks of small fragrant flowers) in lei. In the past, the leaves were used to make a medicinal tea. Hinahina kū kahakai is the island flower of Kaho‘olawe.

Collecting Seeds: Hinahina kū kahakai flower and fruit sporadically throughout the year. The tiny mature seeds are tan or gray, contained inside the dead dried and gray fruits atop the branched flower/fruit stalks. Try to collect the stalks soon after they turn gray since ocean breezes quickly shake the tiny seeds free of the dried fruits. A hand-lens or magnifying glass is helpful for examining the fruits and determining if they still hold seeds. Place the fruit stalks in a clear plastic bag and shake the bag vigorously; the tiny mature seeds will collect in the bottom of the bag for easy retrieval. I have always used relatively fresh seeds, no more than three months old, when growing hinahina. Therefore, I cannot tell you how long they’ll remain viable stored in the refrigerator or freezer.

Growing from Seed: No one grows hinahina from seed – well, almost no one! It’s just so much easier and faster to grow from cuttings. But, for whatever reason, you decide to try, here’s how I do it. I fill one or more 4-inch pots with beach sand and coral rubble. Then, I sprinkle about 20 hinahina seeds on the surface of the sand and GENTLY water them in. I place the pots under 50% shadecloth (but full sun would likely work too) and gently water them every day. After about two weeks you should see the first tiny hinahina seedlings. More seeds will continue to sprout for the next two months. After the first seedlings show, I cut back on the watering and try not to get water directly on the seedlings’ leaves. This helps prevent water-loving fungi from killing the seedlings. After the hinahina have 6-10 leaves, I carefully separate and repot each in its own container. The seedlings grow slowly at first but at the end of six months you should have a nice hinahina six inches or more in diameter. You can speed things up with fertilizer but you will likely get a very unnatural-looking lanky green hinahina that’s more attractive to sap-sucking pests.

Growing from Cuttings: Propagate hinahina from cuttings using either Method One or Method Two. I’ve had better success with younger, still greenish stem-cuttings than older gray-black stem-cuttings. Placing the stems diagonally under the media has also worked better for me than placing them vertically. Be careful not to break the stem when you’re removing the lower (old and new) leaves from the cutting. You should begin to see new roots emerging from numerous nodes in 2-4 weeks. One to two weeks after you first see (or feel) roots, the cutting should have enough root development to remove it from the container (Method One) or mist chamber (Method Two). If you’re using Method Two, take care to adjust the misting frequency so that the cutting’s leaves can dry between mistings; too frequent misting will cause the leaves, and eventually the stem, to rot.

Growth in the Garden: Hinahina planted out in an appropriate environment (i.e., sunny, dry, excellent substrate drainage; see introduction above) grows slowly but steadily, increasing 1-2 feet in diameter per year. Keep a close eye on your newly-planted hinahina until it is well rooted, watering whenever you see serious leaf wilting. After that, cut back on watering to maintain a natural-looking silvery plant. The same is true with fertilizing; too much fertilizer will result in a non-silvery, gangly plant. Hinahina grown from cuttings can start producing flowers soon after establishing themselves in a container or the ground. For hinahina grown from seed, you’ll likely be waiting six months to a year before the first flowers. Hinahina kū kahakai are long-lived plants (if you keep them happy); I know of wild plants that are at least twenty years old.

Diseases & Pests: Occasionally, I’ve seen sucking insects such as mealybugs, scale insects or aphids on hinahina. However, these sickly plants are nearly always living in an unfavorable environment (e.g., too shady, too frequent watering, too much fertilizer). Combat these sucking insects with several sprayings of horticultural oil and a systemic insecticide, and, if possible, try to improve the hinahina’s environment (e.g., move it to a sunnier location).

Ā ā Ē ē Ī ī Ō ō Ū ū