Updated March 18, 2022.
By Erin Buchholz, Integrated Pest Management (IPM) Specialist at the Minnesota Landscape Arboretum
As spring continues on, and more and more of our horticulture staff (myself included) are recalled to work, we are reminded of past struggles. One is the lovely and cheerful spring ephemeral Scilla siberica, or Siberian squill.
You might already realize from its name, this species is not native to Minnesota. Brought here as an ornamental, it can be confused with our native blue harebell (Campanula rotundifolia) or prairie blue-eyed grass (Sisyrinchium campestre). There are also some nonnative lookalikes: Puschkinia scilloides (striped squill), Chionodoxa luciliae (glory of the snow) and Hyacinthoides hispanica (Spanish bluebell).
Siberian squill is a bulb, and it readily propagates itself from seed and bulblets. Some even think it can grow from broken root fragments! Each plant can produce multiple flowers on separate stems or in small groups as a raceme. Each seed head can produce dozens of seeds which usually drop straight down from the parent plant.
What’s to love? The blue hues that show up in early spring bring happiness to those of us waiting for something colorful to signal the change in season. It blooms early, and gradually goes dormant after the seeds mature in late spring, allowing us to enjoy other plants later in the year. Bees love it, too! It’s a tad amusing to see blue pollen color their legs and abdomen after a nice feeding.
What’s to hate? Uff da, that’s a harsh word! It’s not so much that we hate Siberian squill. Rather, we are more concerned for the plants we can’t get established because of Scilla’s greedy real-estate needs.
I playfully put a couple of our horticulturists on the defensive when I ask, “Why do you hate Scilla?” Paul Sotak oversees the Perennial Garden, where it has taken over the understory of some blue beech trees.
“I don’t hate it,” Sotak says. “It’s beautiful, but it’s very invasive. When it naturalizes too much, it’s difficult to get rid of.”
The area under the blue beech is dry shade and sloped — a challenging site already. Sotak is looking forward to replacing Siberian squill with some sedges, which are becoming more popular in the gardening world. Carex appalachica, Carex laxiculmis ‘Hobb’ Bunny Blue, Carex ‘Ice Dance’ and seersucker sedge will provide a soothing solution to our dry-shade problem (assuming we can get the Scilla out).
Fernando Hernandez works with Minnesota-native plants in the Grace B. Dayton Wildflower Garden. Siberian squill has been a frustrating challenge for a while now.
“I work in more natural areas, and Scilla is noticeably choking out native plants,” Hernandez explains. “I’d like to replace it with more of our native spring ephemerals and woodland plants. My biggest challenge is: do we nuke it and start from scratch, or should we try to salvage what is already there knowing that leftover bulblets may undo all our work?”
Two years ago, Hernandez and his team carefully dug out a 5-foot by 5-foot area of Scilla and tried to replace it with a dense carpet of wild ginger. All that remains from that planting are two lonely survivors of that ginger, and a large recolonization of Siberian squill. “A monoculture is not as exciting to look at,” he notes.
Not one to promote the overuse of chemicals (herbicides), I am happy to work with Sotak, Hernandez and our other talented staff members to think of the most effective and safest ways to achieve needed results. While we’ve discovered digging and replacements aren’t that effective, we are exploring less toxic methods like black plastic to cook the soil and bulbs.
Should the time come for herbicide control, we will rely on our pesticide applicator training to ensure visitor, staff and wildlife safety. However, many professionals have found that herbicides are not effective against Scilla due to the thick, waxy leaves and its tendency to go dormant just as it is about to be sprayed. Therefore, I do not recommend herbicides for this pest. We’re going to keep fighting with our hands, tools and wits!