In Mid-Spring, the Charming Red or Pink Flowers of Japanese Primrose Are a Bright Spot of Color in the Seattle Japanese Garden

By Corinne Kennedy

In the Seattle Japanese Garden, Japanese primroses grow along the streams that feed its central pond. (photo: Aleks Monk, 5/6/2012)

The Seattle Japanese Garden is beloved for the brilliant seasonal transformations of its trees and shrubs, but its herbaceous perennials and their quieter beauties also merit our appreciation. One of the most charming and prominent of these non-woody, mostly low-growing plants is Japanese primrose (Primula japonica). Informal clusters grow along the Garden’s streams, in Areas E, F, M, and X. In mid-spring, their red or pink flowers—held above large, crinkled leaves—bring bright spots of color to these wet, partly shady areas.

Primula is a large genus of flowering plants in the family Primulaceae, including more than 400 species. Most primroses are native to the Northern Hemisphere, growing in cool, moist woodlands or high, damp meadows. In general, they perform well in cool, temperate regions, including the Pacific Northwest, but not in hot, dry, full sun locations, where their broad leaves, with numerous microscopic pores (stomata), wilt easily.

The genus name, Primula, is derived from the Latin primus (“first”), a reference to the early blooms of some species. Botanically, Primula is divided into thirty-seven sections—but also, and more simply, into just three basic categories. The Garden’s species, Primula japonica, is the best known and easiest to grow of those categorized as candelabras—primroses native to wet sites and admired for their colorful flowers, arranged in tiers on tall, upright stems.

Primula japonica is vigorous perennial native to Japan, where it is known as kurinsō (九輪草).  In the wild, it grows along mountain streams on Hokkaido, Honshu, and Kyushu. (Unfortunately, its common name, Japanese primrose, is also applied to a related species, Primula sieboldii, known as sakurasō).

Japanese primrose has large, upright leaves that emerge in mid-spring. “Wrinkled, wavy cabbage green leaves,” according to WSU’s Pacific Northwest Plants website, they are light to medium green, oblong, spoon-shaped, and up to 10 inches long, with finely-toothed margins. By late fall, these large leaves decompose, and plants overwinter as low, basal rosettes of small leaves pressed against the ground.   

The brightly-colored flowers of Japanese primroses growing in the Seattle Japanese Garden. (photo: Aleks Monk, 5/6/2012)

Primula japonica blooms later than the dwarf primrose species, with upright flower spikes that usually emerge in late April. Peak bloom is in May, sometimes extending into June. The fragrant flowers appear initially as tight buds in the center of the plant, but over a period of weeks the flowering stems elongate, usually to about 18 inches tall. (When growing in boggy conditions, they are often considerably taller.) Individual flowers, up to an inch across, are held at right angles to the stem, and the flowering stems, when fully extended, have up to six concentric rings or whorls of blooms in various stages of flowering or setting seed. They look a little like an upside-down candelabra. Colors include reddish-purple, red, pink, and white. Several named cultivars have been developed, including ‘Miller’s Crimson’ (bright red flowers) and ‘Postford White’ (large white flowers with yellow eyes).

“Rose, Iris, Primrose and Daisy,” a woodblock print by Japanese artist, Kubo Shunman, 1815. (image: The Metropolitan Museum of Art, Open Access Program)

Primula japonica is frequently cultivated in Japan, but its blooms are not among the flowers most celebrated in Japanese culture and art. Nonetheless, they sometimes appear in woodblock prints or other artworks. In the early 19th century, the woodblock prints of Japanese artist Kubo Shunman featured primroses and irises. The print shown here clearly represents a candelabra species.

Japanese primrose is hardy to USDA Zone 4 (minimum temperature -30 degrees Fahrenheit). Plants grow best in cool, moist conditions—in light to open shade, and in humus-rich soil with a neutral or acid pH.  They also perform well in wet, clay soils, as seen in our Garden, where multiple clumps grow beside the streams that feed its central pond. During our region’s dry summers, plants require regular watering.

When well grown, Primula japonica grows quickly, self-sowing when established. (In wet summer regions, or gardens that are heavily irrigated, this self-sowing may be problematic.) Here, in the Seattle Japanese Garden, they’ve naturalizing in several areas into lovely colonies—natural-looking touches that contrast with the Garden’s carefully pruned trees and shrubs.

Japanese primrose is attractive to butterflies, hummingbirds, and bees. It’s considered rabbit and deer resistant, and has no serious pest or disease problems, though slugs are likely to cause some damage. Meticulous gardeners cut back faded flower stems and damaged or yellowing foliage. New growth will emerge in early fall.

With its lovely, tiered flower stems, Primula japonica is a wonderful addition to moist, shady areas of the garden. Easy to grow—from seed, as well as from starter plants—it’s long-lived in the Pacific Northwest. Although the flowers are said to be excellent for cutting, I prefer to enjoy this charming plant and its blooms in their natural setting. I’m grateful that the Seattle Japanese Garden contains informal, naturalistic areas—with trees, shrubs, and perennials growing as they do in nature—in contrast to its elegantly formal areas, with their expertly pruned and cared for trees and shrubs.

Corinne Kennedy is a Garden Guide, frequent contributor to the Seattle Japanese Garden blog, and retired garden designer.