Native Plants that Drink Responsibly
by Tamara Sherrill
MNBG Executive Director
Many people who have landscaped with native Hawaiian plants conclude that they have awfully specific needs. The plant you thought would be perfect declines from a nearly invisible scale insect or being planted just outside its comfort zone. Hawai‘i’s endemic plants evolved in a geography with widely variable soils, moisture regimes, and temperatures, and many less pressures from pests and diseases. Some are generalists adapted to many elevations, and others only like certain conditions.
There is a cohort of native Hawaiian plants that truly thrive in dry landscapes. These drought tolerant superstars evolved on the leeward low to mid elevation areas, or on windward mountaintops above the inversion zone, which excludes orographic rainfall. Repurposing them for landscaping takes experimentation, but it is absolutely worth the extra effort to create landscapes that preserve Hawaiian cultural heirlooms, conserve fresh water, and reflect the unique beauty of each island’s environment.
Maui Nui Botanical Gardens is a low elevation former coastal dune system with an average annual rainfall of 18 inches. The soil is a pale sand, a highly alkaline Jaucus series soil that can dissipate hundreds of gallons of water in minutes. We have experimented with hundreds of native species and varieties in the past two decades to see which can create a beautiful landscape on a nonprofit budget. Low maintenance? Not quite; but below are a few examples of our favorites. All are long lived, relatively pest free in Kahului, Maui, and extremely water conservative.
Succulents & Other Pot Subjects
Because native Hawaiian plants can be picky as to soil type, we maintain many large planters in our paved areas. These areas are less than ideal for irrigation lines but some plants look good even when we forget to hand water for weeks at a time.
‘Ihi (Portulaca molokiniensis) is a rare endemic that will bloom and grow beautifully if you keep the soil very dry, grow it in full sun, and fertilize regularly. The owers draw many dierent pollinators, and though we don’t have much success growing it directly in our sandy soil, it lives many years in pots. Although all native Portulaca are drought tolerant, P. molokiniensis is relatively pest and disease resistant compared to others we grow.
‘Ala ‘ala wai nui (Peperomia leptostachya) is indigenous (formerly P. blanda var. oribunda) and can survive severely dry soils as well as shade. This native of the black pepper and ‘awa family has dozens of native Hawaiian species that live both as ground dwellers and as epiphytes on trees. P. leptostachya therefore thrives in ltered light or partial sun, and still looks fresh in a drought. It is a perfect rst native plant to give a friend in a small pot, as it does not mind root crowding.
Commonly used native groundcovers or low shrubs such as ‘ilima (Sida fallax), pohinahina (Vitex rotundifolia), and ‘akia (Wikstroemia monticola) are fabulous but there are more species to add to this list with proven drought tolerance.
‘Ilie‘e (Plumbago zeylanica) is more of a beautiful green background than a flowering plant, but it is fantastic at straddling the line between suppressing weeds and not taking over the world. ‘Ilie‘e was used in traditional Hawaiian kakau or tattooing. Probably because the juice from the roots causes a temporary chemical burn if applied to skin for several minutes, deer and other ungulates do not browse on this plant. It is not picky as to sun or shade and can be sheared regularly if you want to be fancy and keep it a certain shape. It is perfect to sprawl in dry shady areas, and the ‘ilie‘e at MNBG that were planted under mature trees in 2001 have never needed pest control or any special attention.
Pohuehue (Ipomoea pes-caprae ssp. brasiliensis) is common on sandy beaches on leeward coasts, but it was once found up to 1,380 feet elevation. It does not need extra water after getting established. A single vining plant can cover a huge area with attractive leaves and purple morning-glory owers, but it is courteous and does not twine or climb. Try wrapping fresh stems of the endemic kauna‘oa (Cuscuta sandwichiana) around established pohuehue vines for an easy lei material source and a beautiful pop of orange each year as it grows and fades; although kauna‘oa is parasitic on pohuehue, it will not hurt it one bit.
Shrubs & Trees
Woody native Hawaiian plants don’t keep their foliage in serious drought, but many mature inhabitants of leeward areas spring back in winter even if stems die back. Some are summer deciduous and need the cycle of losing their leaves in the dry season to be healthy and set owers, which pairs nicely with summer water restrictions.
Naio (Myoporum sandwicense ssp. sandwicense) is unusual in that it can thrive at nearly every elevation. The wood, called ‘a‘aka, was valued for hale construction and for rewood. It can be sensitive to drought at juvenile stages but very tolerant when a mature small tree or tall shrub. There is a Big Island coastal variety with a dwarf habit that is sold as “naio papa” or groundcover naio, which maxes out at several feet tall despite the name and shares all other qualities.
Ko‘oloa‘ula (Abutilon menziesii) is an endangered endemic species in the Hibiscus family that once were common in sugar growing areas. Some know it as “red ‘ilima” and the owers are beloved for lei. Like ‘ilima and other species with grey or silvery leaves, it has minute hairs that help it retain water. As water becomes more restricted, leaves tend to get smaller. Not all endangered species are harder to grow. Some, like ko‘oloa‘ula and our logo plant dwarf naupaka (Scaevola coriacea), were pushed out of their habitats by people but do ne in cultivation.
Wiliwili (Erythrina sandwicensis) and other low elevation summer deciduous trees such as native Polyscias sp. are drought tolerant even at juvenile stages. Though they do lose leaves in summer, wiliwili have a gorgeous bloom along the bare branches. The wood was sought after for surfboards.
These plants grow easily at low elevations, but don’t forget there are also high elevation superstars. Mamane (Sophora chrysophylla) is an essential food source for native birds and maintains its leaves even in drought. This native shrub must grow at 1,500 feet or above. Michelle Smith of Maui Native Nursery says that even the seedlings don’t wilt when they dry out in small pots.
As the global human population grows, fresh water becomes increasingly scarce. Global warming means we need plants in urban areas now more than ever to reduce heat, manage pollution, and create a healthy environment for people. Hawai‘i is no exception, and in addition Hawai‘i has a unique cultural and natural heritage to protect. Our landscapes can include natives while being low maintenance and water conservative if we are willing to experiment and learn.