As winter winds down, many of us are eagerly awaiting the spring color. Woodland ephemeral flowers start off this season, popping up right after the snow melts. Among these early bloomers is Siberian squill (Scilla siberica), whose vibrant blue flowers typically appear in early April.
A popular plant for many home gardeners, the flower isn’t exactly a welcome sight for the Arboretum’s Natural Resource Management team. Although squill is not listed by the Minnesota Department of Natural Resources as an invasive species, it has taken over natural areas of the Arboretum, replacing a diverse sprinkling of spring color with an impenetrable sea of blue. The team has been actively managing the invader, trying to push back a plant that was intentionally introduced.
Squill has many traits that give it a competitive edge over native plants, starting with when it blooms. As an ephemeral, it can photosynthesize during a time most native plants cannot, taking advantage of extra sunlight before trees leaf out. Squill stores its energy in bulbs, a reservoir it can rely on throughout the year. It spreads primarily via seeds but can also form small bulbs from its roots and spread rapidly underground. What’s more, rabbits and other grazers don’t feed on squill, preferring instead the native plants they know and love.
A large patch of Siberian squill in the woodlands by Green Heron Pond. Photo by Jake LaVigne
Like many exotic plants, squill was brought to the United States in the 1700s because of its beloved appearance. It also serves as an excellent cold-hardy ground cover, making it quite popular for landscapers. First planted in the Arboretum’s collections in 1996, squill can be found in many Arboretum gardens, including the Dwarf Conifer Collection, the Terrace Gardens and the Sensory Garden. What gardeners didn’t know, however, when they planted squill, was that it would escape to natural areas. Dense, sizable patches now cover parts of the Wildflower Garden, the Hosta Glade and the woodlands surrounding Green Heron Pond.
Why are large patches of the blue flower such a big deal? Sarah Rademacher, the Natural Resource Management Team Lead, says they’re a threat to native ephemeral plants, including hepatica (Hepatica nobilis), cut leaf toothwort (Cardamine concatenata), snow trillium (Trillium nivale), Dutchman’s breeches (Dicentra cucullaria) and rue anemone (Thalictrum thalictroides).
“The natives struggle to get sunlight and lack space for root establishment. Eventually, the native spring flowering species peter out, while squill establishes a monoculture,” Rademacher explained. When squill overtakes an area, plant diversity declines — along with diversity of the microbes, insects and birds who rely on those plants. Managing squill outbreaks is crucial for protecting ecosystem biodiversity.
Native spring ephemeral wildflowers such as snow trillium (left) and sharp-lobed hepatica (right) are threatened by Siberian squill. Photos by Sarah Rademacher
Developing a plan to control squill has been a challenge for the Natural Resource Management team. They started by digging out the bulbs by hand, a very time-intensive process. The fragile stems tore off easily and left the bulbs to grow back the following year. The team then tried to exhaust the bulbs by mowing above-ground plant tissue in hopes of preventing the plant from photosynthesizing. Unfortunately, they learned the hardy bulbs survived, and native plants were left damaged by the mower.
Searching for a more effective solution, they turned to herbicide, which can have minimal effects on surrounding plants when applied with caution by trained pesticide applicators. “Herbicide is one tool in the integrated pest management toolbox. We start with the least disruptive option, and keep going until we find a solution that balances feasibility and effectiveness,” said Jake LaVigne, a Natural Resources Horticulturist who has been managing squill at the Arboretum for almost a decade. He was able to make some progress against the pest thanks to a combination of careful spot-spaying in dense patches and hand-pulling in more sensitive areas.
The Natural Resource Management team’s experience controlling squill serves as an important model for management in other public gardens that might be experiencing similar issues. As part of the American Public Garden Association’s Sentinel Plant Network, the Arboretum can report plant pests it’s noticed as well as learn from other institutions. Public gardens are often at the forefront of integrated pest management, as they are often the first to see how non-native plants interact with the surrounding ecosystems.
While it may be tempting to plant squill in your garden (or ignore it, if it’s already there), it comes at a cost to your local environment. What might start out as only one or two plants can quickly escalate to an invasion. Minnesota-native ephemerals are a better choice for early spring color without compromising biodiversity. Spring beauty (Claytonia virginica), blue bells (Mertensia virginica or M. paniculata) and woodland phlox (Phlox divaricata) are great options for shaded areas.
For more information about controlling Siberian squill in your own garden, visit the University of Minnesota Extension.
Nina Charlier has been serving as a Minnesota GreenCorps member at the Arboretum since October 2025. She assists the Natural Resource Management team, plant health specialist and arborists in their day-to-day care of the Arboretum grounds. She holds a B.S. in Ecology, Evolution and Behavior Biology from the University of Minnesota.
Cover photo by Jake LaVigne