A tried-and-true native landscape plant

The trend to use native Hawaiian plants in local landscapes is growing, now that endangered species are becoming more available. But the more common Hawaiian plants have a proven place in Hawai'i's landscapes. One such tried-and-true native is pohinahina (Vitex rotundifolia). Other names for this plant are beach vitex, kolokolo kahakai, hinahina kolo, manawanawa, mawanawana and polinalina. Pohinahina is indigenous to Hawai'i. That means it is a native plant here in Hawai'i but it is also native to other parts of the world (from China to Japan to India, in Australia and throughout the Pacific).

In Hawai'i it is found in the wild on sandy beaches, rocky shores and on sand dunes, always near the beach. In cultivation it can be grown nearly anywhere in the lowlands, as long as it doesn't get too much rain. Pohinahina is a sprawling shrub with attractive gray-green/silver leaves.

Pohinahina is in the verbena family (Verbenaceae) and when its rounded leaves are crushed, they emit a spicy fragrance. It doesn't grow much taller than 4 feet, its height depending on the growing conditions (constant wind and salt spray with keep it small). In the wild, it seldom gets taller than a couple of feet, but in cultivation it can reach its maximum height. It responds well to pruning, so its height can be kept in check if a lower-growing ground cover is desired.

This native plant has been used in local landscapes for some time now. It is cultivated on beach areas to bind sand. In landscapes it is used as a tall ground cover when a gray/silver foliage is needed in sunny areas. It can be grown in containers and makes a decent hanging basket if kept pruned regularly. Without pruning, hanging baskets of pohinahina tend to get bare toward the pot as old leaves die back. Regular pruning will force side shoots to grow back toward the roots and create a thicker basket The sprawling habit of pohinahina makes it a nice plant to use on the top of retaining walls, its rounded leaves and trailing branches softening hard features such as the tops of rock or concrete walls. It does well on hillsides, in rock gardens and in lei gardens.

When planted near a walkway its fragrance is released as passers-by brush up against the foliage. Though not planted for its flowers, the pohinahina produces pretty blue to purple flowers in small clusters at its branch tips. Following the flowers are small round, ball-shaped fruits that are tinged with purple when mature. Lei makers like using the pohinahina for its fragrant, gray/silvery foliage, its bluish purple flowers and its ornamental fruit.

Pohinahina is naturally found growing in sand or among the rocks on Hawai'i's shorelines. Being adapted to the harsh conditions found at beaches, it is not too particular as to soil when used in cultivation. It can grow quite well in most soils found in Hawai'i. It does not like to be in soil that is constantly wet, though, and should not be planted where its roots will always be wet. It is very salt and drought tolerant. It performs best in full sun but will tolerate some shade, though its foliage will be sparser and not have its familiar silver sheen. In the winter months, if there is a lot of cloud cover, it tends to thin out a bit, but as soon as the sunny weather returns it will fill out again.

Propagate pohinahina from seeds or cuttings. The individual seeds are hard to extract from the round fruit, so it is best to just plant the whole fruit. Soak fruits for 48 hours before planting and keep the germination medium on the dry side. In three or four months, seedlings will emerge. Transplant them to well-drained potting mix and place them in sunny conditions. By pinching the tips of the young seedlings, you will encourage bushier plants. You can also propagate pohinahina from cuttings. Take tip cuttings when it's not flowering or fruiting. If flowers or fruits are present, remove them before sticking the cuttings. Use a mild rooting hormone and place the cuttings in a well-drained medium and keep moist. The roots will appear in three to four weeks and then you can treat the cuttings as you would seedlings. Pinching will benefit the cuttings (once rooted) as much as it benefits the seedlings - even more so. Some cuttings tend to want to grow with only a single shoot, so pinch regularly until a bushy plant is formed.

Plant your pohinahina in the landscape spaced 2 to 3 feet apart if a quick cover is needed. Weeds will need to be controlled until the plants fill out the area. Once established pohinahina does a good job controlling weeds. If you are planting a single specimen plant, expect it to spread to be about 6 to 8 feet in diameter. You can prune it to keep it smaller. Mulch the new plantings, but once the pohinahina has established itself, don't apply more mulch. The mulch can hold too much moisture, causing more stress than drought would cause.

Though fertilizer is not necessary for survival, pohinahina responds well to compost or chemical fertilizing. Use 8-8-8 granular formulation every three months, or apply compost by broadcasting a thin layer under the branches every three to six months. Regular irrigation is not necessary, but if it doesn't rain for several weeks, pohinahina may lose some leaves. To avoid this, water every couple of weeks if there is no rain. Pohinahina is fairly pest free.

Grasshoppers may occasionally make a couple of holes in the leaves but the damage is never very extensive. Scale insects may become a problem if ants are plentiful. Control the ants and scale in tandem to eliminate this problem. In wet areas, or during the winter, a leaf spot fungus or powdery mildew may appear on the leaves. This will usually clear up when the weather does. If either problem persists, sulfur applications will control it.

Gregory A. Koob Ph. D.
Hawaii Horticulture