Native Hawaiian Garden (7722)

ʻIliahialoʻe (Santalum ellipticum) – An appeal to commercial growers.

ʻIliahialoʻe is a remarkably resilient plant. Often, you can see it alone, growing on highly eroded slopes or as the only native plant in a sea of invasive alien grasses. It is one of the few native Hawaiian plants that can survive and grow back after a brushfire (see photograph below). Why then do we only rarely see ʻiliahialoʻe in residential and public landscapes? Well, there are a few reasons.

For native Hawaiian plant enthusiasts who like to grow their own plants, ʻiliahialoʻe presents a couple of challenges. First, the seeds are not that easy to sprout. They are prone to fungal rot and can take quite some time to germinate if you don't use a pretreatment like gibberellic acid (see Growing from Seed below). Second, ʻiliahialoʻe, like all Santalum species, are hemiparasites, which means the roots of the seedling need to find and attach to the roots of a suitable host plant and extract necessary nutrients in order to survive and grow to maturity. Later, it's believed, most Santalum can survive without this parasitic attachment.

For commercial growers, ʻiliahialoʻe presents unique marketing challenges related to the growing difficulties described above. After successfully sprouting the seeds and growing the seedlings up to several inches in height (after which the seedlings typically stop growing), the seedlings normally have a shelf-life of about a year until they start yellowing and die. Given the difficulty and time spent collecting and preparing seeds and successfully sprouting them, growers often have to attach a significant price tag to these tiny plants. This price, matched with the size of the plant, discourages many potential buyers. Who wants to spend $20 on a six-inch seedling that may or may not survive when they get it home and plant it in their yard? Faced with these marketing difficulties, commercial growers have only occasionally offered ʻiliahialoʻe for sale.

How can we (i.e., I) convince commercial growers to grow and sell ʻIliahialoʻe more often? The answer, I hope, is the results of my mini-experiment (described below). After testing several native Hawaiian host plants, I discovered a few host plants that offer a real opportunity for commercial growers to grow and sell ʻIliahialoʻe-host plant pairs that: (1) no longer have a one-year shelf-life, (2) utilize an easy-to-grow and inexpensive host plant, and (3) include an ʻiliahialoʻe considerably larger than a few inches that the buyer can immediately plant in their yard with the confidence it will survive and grow to maturity.

So, growers, are you interested? If you are, please scroll down and read the section, My Host Plant Mini-experiment. You will not be disappointed, and there's money to be made using this method to expand your ʻiliahialoʻe market.

Habitat & Appearance: Santalum ellipticum is known from Laysan and all the main Hawaiian Islands except Ni‘ihau. However, it is now extirpated from Laysan and Kaho‘olawe and is rare on Kauaʻi. Wild S. ellipticum have been found on ridges, slopes, and in gulches, often on ā‘ā lava or rocky sites, in dry shrublands and forests, often persisting in areas invaded by alien plants, from the coastline to 560[-945] m [Wagner et al. 1990].

Santalum ellipticum varies dramatically in stature, leaf morphology, and even flower color depending on where it is found. However, generally, wild ʻiIiahialoʻe very near the ocean are prostrate or sprawling and have blue-green leathery leaves. As you move inland, the ʻiliahialoʻe you see get taller, first being very bushy shrubs, and then eventually becoming undeniable trees in the uplands. ʻIliahialoʻe leaves also change, becoming less leathery and more droopy (as they hang from the stems). And, while most ʻiliahialoʻe have greenish- or yellowish-white flowers, there are some places like Nānākuli Valley where some ʻiIiahialoʻe have flowers with a reddish tint or red throat; this red flower color may be evidence of a Santalum ellipticum x S. freycinetianum hybridization.

ʻIIiahialoʻe has clusters of perfect (both male and female parts) flowers that are mild to very fragrant. Flowering seems to be sporadic (but more common in spring and summer) in the wild and more continuous in cultivation. Pollinated flowers develop into reddish to dark purple drupes (fleshy fruits with a single-seeded pit) with either a shiny or dull skin.

ʻIliahialoʻe is one of the few native Hawaiian plants that can survive and grow back after a brushfire (Photograph courtesy of Forest & Kim Starr CC BY 3.0 US.). Ripe ʻiIiahialoʻe fruits turn dark red to purple when ripe. This is the time to pick them and not before. Defruited and washed ʻiIiahialoʻe seeds. Note the seeds on the right have had their pointed apex sanded away to improve gibberellic acid absorption by the embryo inside. A young ʻiIiahialoʻe seedling with the clock ticking. Cultivated iIiahialoʻe will assume different forms depending upon their origin. Here is a shrubby ʻiIiahialoʻe typical of coastal areas (Photograph courtesy of Wendy Cutler CC BY-SA 2.0.), and a manicured tree from upland stock (Photograph courtesy of Forest & Kim Starr CC BY 3.0 US.).

ʻIliahialoʻe in Hawaiian Culture: Hawaiians pounded the fragrant heartwood of ʻiliahi and ʻiliahialoʻe into a fine powder and then re-pounded it into newly-made kapa to mask its bad odor, or they would mix the powder with coconut oil to waterproof the kapa [Krauss 1972; Kepler 1985]. The wood was also sometimes fashioned into an ʻūkēkē (musical bow) [Buck 1964], or used as firewood [Wagner 1986]. The wood was favored for making the pola, the platform on a double-hulled canoe [Holmes 1981]. For dandruff and head lice, Hawaiians made a shampoo containing an infusion of ‘iliahi leaves [Krauss 1972].

After contact with Europeans and Americans, ʻiliahi and ʻiliahialoʻe acquired a new significance to the Hawaiian people — a terrible one. Merlin & VanRavenswaay [1990] have provided an excellent description of the Hawaiian sandalwood trade, and I encourage you to read their account. In short, the trade was a devastating example of exploitation and misery for both the elites and non-elites of Hawaiian society.

ʻIliahi is a reference to the reddish color of the plant's new leaves or the tree in general when it is in full bloom [Merlin & VanRavenswaay 1990].

Collecting Seeds: Ripe ʻiliahialoʻe fruits resemble miniature red to black olives. While individual plants typically have ripe fruits for only several weeks, the fruiting season for the species extends from spring through fall. Some plants, particularly those in cultivation, will have more than one crop of fruits per year. Birds, particularly red-vented bulbuls in the lowlands, are attracted to the ripe fruits. Therefore, if you wish to harvest ripe fruits, you should pick them as soon as they turn color, or protect the still-green fruits with a mesh-net bag (e.g., party-favors bag) until they ripen. Do not harvest still-green fruits because the seeds inside will not (normally) germinate.

After your collection, remove the exocarp (fruit skin) and fleshy mesocarp by hand and clean the small endocarp (pit) within; I use a toothbrush to remove all the remaining mesocarp. ʻIliahialoʻe seeds do not store well because the soft oily endosperm and embryo dry out after several months. Therefore, pre-treat (see below) and sow your seeds as soon as possible.

Growing from Seed: My method for germinating ʻiliahialoʻe seeds has not changed much since the 1990s. However, since then, others such as Kroessig & Chau [est. 2015] have run full-scale experiments to confirm the effectiveness of pretreating ʻiliahialoʻe seeds with gibberellic acid to quicken and improve germination.

You can buy gibberellic acid (GA) online from a number of suppliers. While it may cost you more, buy your GA from a reputable company to ensure its purity and activity. Be sure to buy it in powder or crystalline form since pre-dissolved liquid forms are only stable and active for a few weeks. In contrast, GA powder or crystals will remain stable for years if stored in your refrigerator. If possible, buy a GA salt because it will more easily dissolve in water. Otherwise, dissolve your GA in a tiny amount of ethanol (rubbing alcohol) before adding enough water to yield the desired concentration. Some companies will include a tiny spoon and mixing table that make it easy to prepare the GA concentration you want. If the GA you buy doesn't come with a spoon and table, purchase a small electronic scale capable of weighing down to at least one milligram (0.001 gram).

After removing the exocarp and mesocarp and cleaning the endocarp, let your seeds air-dry for about a week. This will improve the absorption of GA; however, Kroessig & Chau [est. 2015] were still successful after letting their seeds dry for less than 24 hours (i.e., overnight). Using a small square of sandpaper, sand away a small portion of the endocarp from its apex (pointed end) so you can just barely see the white embryo inside; proceed slowly so you don't damage the embryo (see photograph above). This scarification will also enhance the direct absorption of GA by the embryo. However, this time-consuming step is not a required since Kroessig & Chau [est. 2015] had success without the scarification — it just took their seeds a bit longer to sprout (i.e., two months versus one month). Soak the seeds in a shallow solution of 500 ppm (0.05%) GA for five days, changing the solution daily. Again, Kroessig & Chau [est. 2015] had success with only a 24-hour soaking, and with GA concentrations as low as 100 ppm (0.01%); however, seeds soaked for a shorter time and/or in lower concentrations germinated later than seeds pretreated using my method. Remove the seeds from the GA solution and dust or dip them in a fungicide. I normally use a 1:1 mix of powdered sulfur and Captan. This will help inhibit any fungus from infecting and killing the seeds. Finally, sow your pre-treated seeds in a covered tray (to protect them from pests like rats and birds) of moist vermiculite using Method One.

GA-pretreated ʻIliahialoʻe seeds should begin sprouting in about two weeks, with continued sprouting for another one to two months. After two months, about 90% of your seeds should have sprouted. Promptly remove any seeds that show signs of rot (i.e., discolorization, liquidification, foul odor) before they can spread the rot to other seeds or seedlings. Allow the seedlings to grow an additional one to two weeks and develop their first true leaves (see photograph above) before VERY gently transferring them to their host plant's pot. Maintain the potted plant pair in a safe place (e.g., nursery, indoors) under bright natural (50% to 75% full sun) or artificial (e.g., LED) light, and water regularly. It typically takes a couple of months for the roots of an ʻiliahialoʻe to establish connections with the host plant and there is little above-media growth during this period. After connecting, the seedling will begin growing taller, often with its leaves becoming a darker green and becoming tinged red, purple, or blue. Growth then is moderate with the seedling taking about six months to reach 12 inches in height.

ʻIliahialoʻe seedlings seem to need iron. Therefore, if the host-plant potting media is deficient in iron and your ʻiliahialoʻe remains off-color (e.g., yellow, light green) or barely grows, try applying a balanced controlled-release fertilizer with minor elements (including iron) every three to six months. Alternatively, give it a foliar feeding of an organic or inorganic water-soluble fertilizer containing iron diluted to ⅓ to ½ the recommended strength every couple of months. A good direct source of iron is iron chelate, which you can buy in either a liquid or granular form. Apply the iron chelate two to three times a year as directed.

Within their host-plant pot, ʻiliahialoʻe seedlings are occasionally attacked by sap-sucking insects such as aphids, mealybugs, and scale insects. Refer to Enemies in the Garden for treatments.

Note: The above pretreatment is a lot! Therefore, if you're not willing or able to use a GA pretreatment, you should know that other researchers have had some success sprouting non-Hawaiian Santalum species by successively drying and wetting the seeds until they cracked and then sowing the cracked seeds. However, just cracking the seeds (endocarp) manually doesn't improve germination — I've tried!

Growing from Cuttings: I have never attempted to grow ʻiliahialoʻe from cuttings. Some researchers have tried with non-Hawaiian Santalum species, but they have had little to marginal success [Vennila et al. 2023].

My Host Plant Mini-experiment: In November 2024, I collected ripe fruits from a single large wild shrubby ʻiliahialoʻe growing in Kalaeloa, O‘ahu. This plant was about a quarter-of-a-mile away from the ocean, and, therefore, had thinner leaves than those typically seen along the coastline (e.g., Ka‘ena Point, Makapu‘u). The seeds were immediately extracted, washed, scarified, and treated with gibberellic acid as described in Growing from Seed above. Once a seedling had developed its first two true leaves (i.e., 1 to 2 weeks after germination), it was placed in the pot (3.5"x3.5"x5") of an established host plant (see species list below). The potted-plant pairs were then placed under LED lamps within my air-conditioned (75°F) apartment and watered regularly. After one year (November 2025), the height of each ʻiliahialoʻe seedling was measured to the nearest half-inch. Because of the limited number of ʻiliahialoʻe seedlings and my desire to test as many native Hawaiian coastal plant species as possible, I decided to pair only one or two seedlings with each host species; yes, I know, an embarrassingly poor experimental design with minimal or no replication! Below is the raw data along with the average height in inches of all the one-year-old ʻiliahialoʻe seedlings for each host species, listed from the poorest growth to best.

Ipomoea pes-caprae subsp. brasiliensis — 3, 4 (avg 3.5)
Plumbago zeylanica — 4, 5 (avg 4.5)
Achyranthes splendens var. rotundata — 5
Lycium carolinianum var. sandwicense — 5
Myoporum stellatum — 7
Scaevola taccada — 7
Solanum nelsonii — 7
Vitex rotundifolia — 9, 12 (avg 10.5)
Gossypium tomentosum — 12
Sesbania tomentosa — 4, 23 (avg 13.5)
Chenopodium oahuense — 9, 18 (avg 13.5)
Sida fallax — 22, 23 (avg 22.5)
Jacquemontia sandwicensis — 23 & one dead
Sesuvium portulacastrum — 24, 36 (avg 30)

As you can see, ‘ākulikuli (Sesuvium portulacastrum) and ‘ilima (Sida fallax) were by far the best host plants for the ʻiliahialoʻe seedlings. This is indeed fortunate, since both ‘ākulikuli and ‘ilima are common and easy to grow from cuttings, ‘ākulikuli particularly so. Therefore, I strongly recommend commercial growers use ‘ākulikuli as their host plant-of-choice when growing and selling ʻiliahialoʻe because it yields the maximum ʻiliahialoʻe seedling growth AND will add the least overhead price to the potted-species pair.

Twelve of the 14 tested host plant species, each with their ʻiliahialoʻe seedling at the start of the mini-experiment. One-year-later results: two examples each (from left to right) of poor, okay, and best host plants; ‘ilie‘e and pōhuehue, ma‘o and pōhinahina, ‘ilima and ‘ākulikuli, respectively.

Growth in the Garden: When your ʻiliahialoʻe seedling reaches 12 or more inches in height, the host plant and ʻiliahialoʻe pair is ready to be planted in the ground. Select a site that receives full sunlight for all or most of the day for optimum growth and health. ʻIliahialoʻe don't seem to be very fussy about soil type and will grow in sandy or coralline soils, lava/cinder, clay, and even heavily degraded or eroded soils. Just after planting, keep a daily watch on your seedling. If it shows any signs of water-stress such as wilting, give it a drink and consider constructing a temporary "umbrella" to shade it. You will know it has established itself in your garden when it puts out a flush of new leaves. Also keep watch for chewing pests (e.g., snails, cockroaches) which can girdle the young ʻiliahialoʻe (see Diseases & Pests below).

After your ʻiliahialoʻe is established and growing, water it approximately once a month during the dry months of the year. Do not overwater an established plant since this can kill it; black sooty mold on its leaves is one indication you are overwatering. ʻIliahialoʻe can tolerate extreme heat, drought, and strong winds. Coastal types are tolerant of salt spray.

Established ʻIliahialoʻe grow at a moderate rate, and you can expect your plant to be about two feet tall one year after planting. After two years, expect to see the first set of flowers.

Often, the soil will provide enough iron and other nutrients such that ʻiliahialoʻe will not require fertilizer. However, if your ʻiliahialoʻe yellows or barely grows, try applying a balanced controlled-release fertilizer with minor elements (including iron) every three to six months. Alternatively, give it a foliar feeding of an organic or inorganic water-soluble fertilizer containing iron diluted to ⅓ to ½ the recommended strength every couple of months. A good direct source of iron is iron chelate, which you can buy in either a liquid or granular form. Apply the iron chelate two to three times a year as directed.

Avoid pruning your ʻiliahialoʻe unless it is absolutely necessary, and then only prune by hand in stages over time. Additionally, make sure the host plant does not heavily shade your ʻiliahialoʻe and prune it if needed. Be careful using any herbicides around ʻiliahialoʻe because of possible root connections between your plant and the weeds you are trying to kill. The safest course of action is to always weed by hand around your plant. Merlin et al. [2005] recommend that "weeds within a radius of the tree equal to about twice its height should be" removed by hand or machine.

Diseases & Pests: ʻIliahialoʻe in the ground are able to resist most pest attacks, but may infrequently become infested by scale insects or whiteflies. Insects such as cockroaches and sowbugs or snails and slugs will sometimes chew on the main stem/trunk of ʻiliahialoʻe at ground level. This is potentially fatal for young plants. Refer to the Enemies in the Garden page for ways to protect your ʻiliahialoʻe from or deal with these pests.

Ā ā Ē ē Ī ī Ō ō Ū ū