Spirea: The Good and the Bad

Spirea has become a common shrub in our gardens and parks. Its white, pink, and rose-red flowers that may rebloom throughout the season attract pollinators, including bees, butterflies, and hummingbirds. Its foliage is green, often with hints of yellow or red. It is easy to maintain and not fussy about soil or light conditions. Spirea has few pests or diseases. Usually, deer do not damage spirea. These are certainly appealing characteristics, but are there disadvantages to planting spirea? Yes, if you select the wrong species. So, what are the good spirea and what are the bad spirea in our landscapes?

Spirea Overview

The genus Spiraea comprises over 80 species in the rose family (Rosaceae). They are native to the northern hemisphere, with the greatest diversity in Asia. Several species are native to North America, including in Pennsylvania. Some plants that my family called spirea have been separated into other genera. False spirea, for example, is now Sorbaria sorbifolia. You may know 'Sem' and Mr. Mustard from your local nursery. The queen of the prairie, a beautiful native perennial with showy bright pink flowers, is now classified as Filipendula rubra.

White-Flowering Spirea

Let's start in the early spring. One of my favorite spireas, the bridalwreath spirea (Spiraea x vanhouttei), is a hybrid of two Asian species, S. trilobataandS. cantoniensis. The shrub is vase-shaped, with long, arching branches bearing flower clusters about 2 inches wide, full of numerous single white florets. Its blue-green leaves are unremarkable in autumn. Often, there is confusion because another Asian species, Spiraea prunifolia, also shares the common name "bridalwreath." Its white flowers are borne in small clusters of three to five doubled florets on upright branches. The shrub is about as wide as it is tall, rather than vase-shaped. In autumn, the foliage turns yellow, orange, and red before falling.

Thunberg spirea (Spiraea thunbergii) is another early white-flowered bloomer. Its leaves are willow-like, turning bronze-orange in autumn. The cultivar 'Ogon', also called Mellow Yellow, has bright yellow leaves in early summer. Another white spirea is S. nipponica, the snowmound spirea. This smaller Asian species does not bloom until May or June. Its foliage turns golden yellow in autumn.

Birchleaf spirea (Spiraea betulifolia) is a small, rounded shrub. Its white flowers appear in early summer against dark green, birch-like leaves. For seasonal interest, the leaves become red, orange, and purple in autumn. But if you want a pop of color early in the growing season, look for Glow Girl with light golden leaves. Each of these white-blooming spireas, though non-native, tends to be well-behaved in the landscape.

Native Spirea

Are there spireas for those who prefer native plants? Yes! Our native spireas include meadowsweet, steeplebush, and Virginia meadowsweet. Meadowsweet (Spiraea alba) and steeplebush (S. tomentosa) have terminal panicles and vertical clusters of flowers. Meadowsweet flowers are usually white, but may be pinkish. It is native to the eastern United States and Canada, and is generally found in very moist soils. Steeplebush, sometimes called hardhack, has pink flowers.

Virginia meadowsweet (Spiraea virginiana) is a rare native spirea with white, round clusters of flowers at the tips of branches. It is found in the southern Appalachian Mountains. Once found in Fayette County, Pennsylvania, damming the Youghiogheny River changed its habitat. It is federally listed as threatened. Occasionally, it is found in cultivated gardens.

Native spireas bear very few viable (fertile) seeds. Instead, they spread by underground runners, creating patches of shrubs.

Japanese Spirea

In June, look around your neighborhood for a beautiful mounded spirea with 3 to 6-inch-wide pink to rose-red flat-topped flower clusters called corymbs. I promise it will be easy to find. The Japanese spirea (Spiraea japonica and its hybrid S. x bumalda) has been extensively planted in our landscape. Japanese spireas are beautiful and carefree shrubs. New foliage may be russet-orange to bronze-red. The leaves of 'Goldflame' change from russet to soft yellow to green. In Japanese spirea, the foliage appears before the flowers, and there are many choices of flower and foliage colors. These shrubs are tolerant of most soil and light conditions. Gorgeous Japanese spireas remain beautiful because they tend to be deer-resistant.

Unfortunately, they spread their tiny, abundant, fertile seeds far and wide. Look carefully, and you will find young seedlings, often in bloom, beside their established parents. Depending on the area, you may find them along the roadside, too. 'Little Princess' and 'Anthony Waterer' are among the decades-old varieties responsible for the unplanned, unwanted spread that outcompetes native vegetation. Some of the newer cultivars of Japanese spirea are marketed as "sterile". Only time will tell if these varieties are non-invasive.

The Controlled Plant and Noxious Weed Committee of the Pennsylvania Department of Agriculture voted not to add Japanese spirea to the noxious weed list at this time. Adding a plant to the noxious weed list is a decision that cannot be made lightly. Stay tuned for updates.

What Can You Do?

Breeders are creating truly sterile cultivars of our favorite but invasive plant species. Like developing effective medications, making them takes time and testing to verify their safety. Consider purchasing spirea species native to our area, or, if exotic, non-invasive. Do not purchase any cultivars of Japanese spirea that are not labeled "sterile."

If you already have Japanese spirea in your landscape, consider removing it and replacing it with a similar, but non-invasive plant. Ninebark (Physocarpus opulifolius) is a native shrub and similar to spirea. Ninebark cultivars have colorful foliage and clusters of white or pink flowers. If you are unable to replace the Japanese spirea plant, be sure to remove its spent flowers (deadhead) before the seeds mature. Discard the dead flower heads in the trash, not in the compost pile. Do your best to reduce the invasive plant populations in your area.