Euphorbia in Hawaiian Culture: Given the very limited habitat of this plant, it's not surprising that it has escaped recorded Hawaiian reference. With friends and volunteers, I often refer to E. haeleeleana as the ‘akoko tree. Like other ‘akoko, it’s possible Hawaiians utilized the white sap for medicine.
Collecting Seeds: Female trees produce large (3/4 to 1 inch diameter), ripe, yellow-brown, woody fruits in late summer and early fall. Do not collect still-green fruits because they will not contain viable seed. At home, dry the fruits for several days in a paper bag. Some of the fruits will explode and release their seeds. For the others, crack them open with pliers to get at the seeds. Seeds remain viable in the refrigerator for about a year but then begin to lose viability.
Growing from Seed: Sterilize (with 10% bleach for 15 minutes) and then soak the seeds for 1-2 days in a shallow pan of tapwater. Using Method One, the seeds will begin to sprout in 1-2 weeks and continue for another couple of weeks. Because of the seedlings' rapid initial growth, I transplant new seedlings to individual pots just prior or with the development of their first true leaf. (Rather than using Method One, you might try Method Two, but only with very clean media and surroundings.) I move the seedlings into the nursery (50% sunlight) 1-2 weeks after transplanting them to individual pots. They grow quickly in the light along with a bit of fertilizer. Avoid overwatering because this will cause the seedling to rot and die. After 3-6 months in the nursery, the plants should be 8-10 inches tall and you can safely plant them out into the garden.
Growing from Cuttings: I have not grown this plant from cuttings.
Growth in the Garden: I have only planted Euphorbia out into sunny, naturally watered areas (i.e., I do not irrigate) where most of the rain falls during the winter months. During the wet season, the plants grow rapidly, adding 1-3 feet to their height each year. During the dry summer months, they lose all or most of their leaves and go dormant. My guess is that if you lightly watered your Euphorbia during the dry season, it would grow more rapidly. Naturally-watered Euphorbia mature and begin flowering after 4-10 years (6-10 feet tall). Of course, you will need at least one female and one male plant for viable seed production.
Diseases & Pests: Euphorbia are attacked by scale insects as seedlings in the nursery and in the garden. Stems, leaves, and roots are all vulnerable. You can often remove all or most of the scale insects on the stems and leaves by hand. Below ground, you will need to use an insecticide (see Enemies in the Garden). I have also had a few plants die from rot at their base but am not certain of the cause.
Ā ā Ē ē Ī ī Ō ō Ū ū