Olopua (Nestegis sandwicensis) – Taking its time.

If I had to list all the reasons native Hawaiian plants remain uncommon in the residential yards and gardens of Hawai‘i in spite of the public's interest in our native flora, near the top of that list would be: (1) how difficult it is to propagate some species, and (2) how long it takes to grow many native plants to a respectable size. Of course, there are numerous exceptions such as ‘a‘ali‘i, koa, ma‘o, ‘ohai, and pōhinahina, which are all easy to propagate and quickly grow to maturity (i.e., flowering and fruiting adult plants). Unfortunately, olopua is not one of these exceptions, being both difficult to propagate and slow to grow into a sizable tree.

One has to wonder why different plants have evolved different developmental paths, some sprouting and growing quickly (e.g., ‘ohai), others germinating quickly but then growing slowly (e.g., lama), and some like olopua taking their time to both germinate and grow to maturity. Some botanists have proposed that the slow growth of many native Hawaiian plants is the result of the very benign conditions (e.g., few or no herbivores, pests, and diseases) prior to humans arriving in the Islands. Others have suggested the general lack of the intense competition between plants commonly seen in continental tropical and subtropical plant communities permitted Hawaiian plants to develop more slowly. Unfortunately, testing either of these two hypotheses is extremely difficult because we are dealing with evolutionary timespans, something considerably longer than the lifespan of botanists.

Olopua in Hawaiian Culture: Hawaiians fashioned the very durable hardwood into spears, digging sticks, adze handles, daggers, and rasps for making fish hooks. The wood was also used for posts and rafters in hale. Olopua was a preferred firewood, because it burns with a hot flame even when green.

Collecting Seeds: Look for ripe purple to black fruits during the summer. Unfortunately, ripe fruits do not always contain viable seed. Typically, fruits with viable seed are larger than those without. Additionally, if you extract the seed from the endocarp, viable seeds often have a hint of green tissue visible. If possible, collect ripe fruit directly from the tree since fruit from the ground is likely to have been attacked by borers or disease. Back at home, sterile the outer surface of all the fruits for 15 minutes in a 10% bleach solution. I have always attempted to germinate olopua seeds immediately after collecting them, so I cannot comment on seed storage.

Growing from Seed: There is a real dichotomy in the experiences of people who have tried to grow olopua from seed. A few of the many people I have spoken to said they had little to no difficulty sprouting olopua seeds and growing the seedlings to a significant size (i.e., 12 inches), although they all reported germination was slow (3-12 months). Similarly, I have routinely seen olopua seedlings beneath wild trees at some of the montane sites I have hiked to on O‘ahu. In contrast, me and many others have had little to no success in growing olopua from seed, either because the seeds failed to germinate or the germinating seed died. Collectively, these contrary experiences suggest to me that there is some type of deadly microbe common within the lowland nurseries (or even inside my apartment) where I and others have attempted to sprout olopua seeds, and that this microbe is absent at more upland wild sites and nurseries. With this preface, below I describe my best success at growing olopua from seed using a seed extraction method.

After sterilizing the fruits, remove the exocarp (i.e., fruit's skin) and mesocarp (i.e., fruit's flesh) of the fruits by hand or with a colander, leaving the stony endocarp with the seed sealed inside. Re-sterilize the outer surface of the endocarp in a 10% bleach solution for 15 minutes. Allow the endocarps to air dry for 1-3 days, after which they should be hard (i.e., non-pliable to finger pressure). Carefully, using a small C-clamp or pliers, crack the endocarp along its midline and extract the seed with your fingers or a set of forceps. (This procedure reminds me of cracking open pistachio nuts.) The seed will still be covered by a papery seedcoat; do not remove this seedcoat. The photograph to the right shows the dried endocarp and extracted seed for comparison. Immediately sow the seed horizontally in a bed of vermiculite (i.e., Method One).

Examine the sown seeds daily, and immediately discard any that show signs of rot. (If you are unsure, gently squeeze the seed; a rotten seed will typically exude a putrid fluid.) After 1-2 months, you should see a root emerge from the pointed end of the seed, and about a month later the sprout will grow upright and shed its papery seedcoat (photographs to the right show this development). Avoid the temptation to 'help' the seedling by pulling on the seedcoat since you may decapitate it. Rather, a light misting once a day is the safest help you can provide.

Growing from Cuttings: The few times I have tried to root olopua cuttings (using Methods One or Two) have all failed. Lilleeng-Rosenberger (2005) has rooted green softwood cuttings collected in mid to late summer using rooting powder (Nos. 3-8) under a mist system; the cuttings took 3-4 months to root.

Growth in the Garden: My past difficulties with propagating olopua have limited my experiences with this species in the ground to several plantings more than a decade ago at a restoration site in Wai‘anae, and, more recently, a few plantings within the Teaching Gardens at Leeward Community College. At both sites, I decided to plant the olopua in full or partial sunlight based on where I have seen them growing in the wild. To date, most of these plants are still alive but have grown very slowly. For example, the oldest Wai‘anae plantings, now 12 years old, are still less than six feet tall. The olopua that have died appear to have succumb to drought; lack of rain at the restoration site and an unnoticed failure with the irrigation system in the Teaching Garden.

All of my limited plantings have been at low elevations (i.e., less than 500 ft). In contrast, friends have told me they have one olopua they planted ten years ago on their Olinda, Maui, property that is now 12 feet tall and producing flowers and fruit. So, it may be that olopua does best in cooler upland sites.

Diseases & Pests: To date, scale insects are the only pests I have seen on some of the small olopua I have grown in the nursery. These were eliminated with a few sprayings of horticultural oil. However, it is reported that the black twigborer (Xylosandrus compactus) devastated wild olopua populations in the latter half of the 1900s, and that many of the remaining trees look more like shrubs today because of repeated attacks that continue to the present.

Ā ā Ē ē Ī ī Ō ō Ū ū