Pittosporum tobira: Sweetly Fragrant Spring Flowers and Glossy Green Foliage
By Corinne Kennedy
A very young Pittosporum tobira shrub, planted on the hillside north of the Seattle Japanese Garden’s central pond, Area O. (photo: Corinne Kennedy)
This is the final article of a three-part series featuring little-known broadleaf evergreen shrubs recently added to the Seattle Japanese Garden. (The first article, posted in February, was about Distylium. The second article, about Leucothoe, was posted in May.)
My subject this month is Pittosporum tobira, commonly known as Japanese pittosporum or Japanese mock orange. Three small shrubs were planted in 2021 on the hillside at the northern end of the Garden (Area O), just west of a 75-foot-tall Norway spruce (Picea abies). With glossy, dark green foliage that’s attractive throughout the year, it was an excellent choice to replace the failing semi-evergreen euonymus shrubs (Euonymus kiautschovicus, known as spreading euonymus) previously planted there.
Broadleaf Evergreens in the Seattle Japanese Garden:
Broadleaf evergreens, even those without showy flowers, are arguably the most important plant type in the gardens of Japan. With their evergreen foliage and strong form, they contribute mass and structure in all seasons. Unfortunately, when the Seattle Japanese Garden was constructed in 1960, garden creator Jūki Iida was unable to source the broadleaf evergreens used in Japan. Perhaps reluctantly, he agreed that rhododendrons, which were popular in the Seattle area, could serve as substitutes. In the years since then, as more broadleaf evergreens have become available, the Garden’s plantings have become more diverse.
Camellias and the larger-growing rhododendrons, with their attractive flowers and tree-like proportions, often serve as specimen or focal-point plants. Yet the more compact, smaller-growing, and smaller-leaved broadleaf evergreens are also important—as “supporting cast,” often pruned in the low, spreading shape known as tamamono. The desired form is semi-spherical, not the ball-like form used in Western-style topiary. Shaped to be at least twice as wide as tall, with the widest part touching the ground, they resemble deeply buried stones. This basic mounded shape adds a dimension, present throughout the year, that contrasts with the horizontality of the ground plane and the verticality of upright-growing trees and shrubs. Its repetition brings mass and stability to Japanese gardens and helps to establish their characteristic simplicity and tranquility.
Pittosporum tobira:
Pittosporum tobira is a broadleaf evergreen shrub or small tree native to central and southern Japan, where it is known as tobera. It is found there—and in the southern areas of China, the Korean Peninsula and Taiwan—from sea level to elevations of about 6000 feet. Native habitats include seashores, rocky hillsides, forests, and roadside openings. It is most often known as Japanese mock orange, Japanese pittosporum, Japanese cheesewood, and tobira. Unfortunately, it is also called simply mock orange, a common name given to many other plants.
The genus name Pittosporum, meaning “pitch seed,” was derived from the Greek words pitta (“pitch”) and spora (“seed”) and refers to the sticky seeds of many members of this genus. The Japanese word tobera became its specific epithet in 1712, but later in that century the spelling was altered to tobira.
Japanese pittosporum is a dense, mounding evergreen shrub—in warm regions, about 15 feet tall and 12 feet wide at maturity. Although native to Asia, it is a long-lived and nearly indestructible plant that has become a popular ornamental worldwide, particularly in Mediterranean climates and in the southeastern United States. The glossy, dark green leaves (duller, matte green beneath) are leathery in texture, oval-shaped, and broadest at their tips. From one to five inches long, they have rolled margins, and are arranged in whorls along the stems, contributing to the plant’s very dense appearance.
Flowers and foliage of Japanese pittosporum. (photo: Jim Evans, Wikimedia Commons)
A late-spring bloomer, Pittosporum tobira bears small five-petaled flowers in terminal clusters, aging from white to creamy yellow. Their sweet fragrance resembles that of orange blossoms—hence the common name Japanese mock orange. Three-valved green fruits ripen to brown in the fall but are often hidden behind the leaves. When mature, the dry capsules split open to reveal showy orange-red seeds.
Adaptability and Ornamental Uses:
Japanese pittosporum is a tough, durable shrub, hardy to USDA Zone 8 (minimum temperature 10 degrees Fahrenheit). It thrives in full sun or part shade and tolerates drought, heat, salt spray, and a range of soil types and pH. Good drainage is essential, however, or death from root rot disease is a likely outcome. This adaptable shrub is tolerant of regular pruning and is easily transplanted.
Although drought-tolerant and without major insect or disease problems, Japanese pittosporum is healthiest and most attractive when grown in a warm location and provided with sufficient irrigation, especially during establishment. Stressed plants are more likely to develop leaf spot, aphid or scale infestations, or other problems.
Pittosporum tobira also contains chemicals known as saponins, which are also found in foods, including some legumes. Although toxic to people, saponins are poorly absorbed by the body and generally do not impact human health. They are also broken down when foods are thoroughly cooked. Fortunately, this shrub is also non-toxic to dogs, cats, and horses.
Mature Pittosporum tobira shrub growing in Los Altos, California. (photo: S.G.S., Wikimedia Commons)
Although Japanese pittosporum has stiff branches and a dense, spreading habit, it takes very well to regular and even severe pruning. Flowering may be sparse, but it can easily be maintained at three to five feet tall and wide—as a tall groundcover, a low mounded shrub planted singly or in drifts, or a foundation plant. It makes an excellent formal or informal hedge or screen, as well as a seashore buffer against salt spray and wind. With careful pruning and removal of the lower branches, it will become an attractive, multi-stemmed small tree. In all applications, even when grown in a container, it brings structure and vibrant evergreen color to the garden.
Pittosporum tobira is popular and even commonplace in the southeastern U.S., though not in the Pacific Northwest. With its sweetly fragrant spring flowers and glossy, rounded, deep green foliage, it should be more widely known and planted here—especially as we adapt to the realities of climate change. Fortunately, dwarf cultivars are also available at local retail nurseries and will prove easier for interested gardeners to maintain at a size appropriate for small city gardens. Popular examples are P. tobira ‘Wheeler’s Dwarf’ and P. tobira Cream de Mint™, a variegated form.
The three young plants on the hillside north of our pond are still becoming established and remain very small. In the coming years, I invite visitors to acknowledge their smallness and at the same time visualize the beauty and structure they will ultimately bring to the Garden.
Corinne Kennedy is a Garden Guide, a frequent contributor to the Seattle Japanese Garden blog, and retired garden designer.