False spirea (Sorbaria sorbifolia) is beginning to bloom. Not much information about this plant is found beyond gardening websites, but it may be a species to watch in the Adirondack region. Why is there cause for concern? False spirea is an ornamental plant available for home gardens, but populations have been found growing in dense monocultures in natural areas. Stands of the plant are near Lampson Falls along the Grasse River, along the west branch of the Ausable River near the ski jumps in Lake Placid, and along the east branch of the Ausable River near Marcy Field in the Town of Keene. All are found outside of cultivation, and their proximity to water makes dispersal of seeds easy and uncontrolled.
Some plants, such as purple loosestrife, (Lythrum salicaria), are recognizable invaders. Loosestrife is widespread across much of the country and its impacts are well-known and well-documented. Other invaders, however, may be just beginning to get established and may go unnoticed as problematic plants, leading a quiet expansion across the land. Once we take notice, it may be too late. False spirea may be one of those plants, or it may be a plant that is an aggressive spreader locally but may not leap to new areas unassisted.
A perennial introduced from Asia, false spirea is also known as ash leaf spirea, false goat's beard, and Ural false spirea. It is a multi-stemmed, deciduous shrub growing 5 to 8 feet in height and spreading just as wide. Its dark green foliage is compound, alternate and toothed and resembles that of American mountain ash (Sorbus americana) or various native sumacs (Rhus spp.). It is most apparent when it blooms in June and July, having dense plumes of white flowers clustered at the end of branches.
(Photo — Hilary Smith)
Some gardeners proclaim the benefits of the plant, such as fast growth and lush foliage. Others offer a warning. One gardener provides the following quip, "It will spread by root suckers (stoloniferous roots), so be sure to remove the new plants it you do not want an entire colony, or goodness, an entire village of them in your yard! This plant can be invasive. You might want to consider giving your false spirea a good haircut by mowing it to the ground occasionally to keep it under control."
Restorationists and nursery owners in Southern Ontario took notice of false spirea in 2002, categorizing it as moderately invasive, which reinforces why we should be on the alert here. They note that Sorbaria can become locally dominant when the proper conditions exist and recommend controlling it where necessary and limiting its spread to other areas. It typically grows in sunny meadows or edge habitats with moist but well drained soils but can tolerate forest understory, too.
Do not confuse false spirea with our many native spirea, such as steeplebush (Spirea tomentosa) or meadowsweet (Spirea alba), ornamental astilbes (Astilbe japonica) which are sometimes also referred to as false spirea, or native elderberry (Sambucus nigra ssp. canadensis). These plants, plus others such as goat's beard (Aruncus dioicus), can be good alternatives to Sorbaria.
If false spirea is part of your garden plan, take note to keep its spread in check. If you have experience with this plant, or if you see it in natural areas while traveling the park, call the Adirondack Park Invasive Plant Program so that we can better understand its distribution and whether it is scenic or sinister.
Eye on Invasives is a biweekly column that spotlights a top invader when it is easiest to identify. Hilary Smith directs the Adirondack Park Invasive Plant Program, a partnership program housed at the Adirondack Chapter of The Nature Conservancy in Keene Valley, NY. Find out more about this award-winning program online at www.adkinvasives.com.