Arboretum News

Pretty, but aggressive squill

Meet Siberian squill, a cheerful, yet invasive spring ephemeral.

COVID-19 Update: The Minnesota Landscape Arboretum reopened in a limited capacity on Friday, May 1. As a key part of the University of Minnesota’s research and outreach missions, we have been working with University leadership on a phased approach to ensure visitor and employee safety as we welcome you back. Find updates and information here.

Siberian squill. Photo by Erin Buchholz.

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.

Scilla growing in the middle of ground-cover juniper. Photo by Erin Buchholz.

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!

For more information, please visit University of Minnesota Extension.  Any other questions, please let me know at buchh006@umn.edu.  I’ll do my best to help!

6 comments on “Pretty, but aggressive squill

  1. I would love to know what you continue to do. I have Squill taking over on the small back hill. It is mixed in with so many other plants so I am not happy about digging it all up but on the other hand is I just chemicals it will kill off the other plants as well. Funny that you used wild ginger I have done the same here. So far the ginger is winning in one area! Thanks

    • Hi Joanne, we are going to continue manual removal for now, but we will also try to put down some pre-emergent herbicide to try to help prevent the seeds from germinating and taking over. You gotta be quick with that stuff, though. Once the seeds start to germinate, it’s too late. Plus, you can’t disturb the soil surface afterward, or the chemical layer won’t work to prevent their growth. Any more questions, please email me and I will try to help.

  2. Lila M Smith

    The Squill were here when we bought our house over 40 years ago. It is pretty and I’m glad the bees like it, but I’m trying to transition to mostly native plants. Should I consider pulling out squill when the ground is moist? I haven’t removed it in the past, but did notice bare root natives I planted near them didn’t do as well. In one area I am fighting them with an aggressive native: Common Blue Violet and am pleased with the result. I do have Wild Ginger beneath my Serviceberry and it is doing well despite some Squill amongst it.

    • Hi Lila, wet soil is often easier to weed. The biggest thing is to pull them before they set seed! Plus, the bulbs often send out their own little runners which seem to anchor them down better, if not also multiply themselves. So it’s best to get as much of them out as possible. I’m glad to hear you’re having some success with more aggressive natives. We’ll have to keep trying, too!

  3. Ralph J Yehle

    My wife likes Squill and we have a small area of it that isn’t expanding very fast at this point. Our garden nemesis is Campanula rapunculoides we both agree. With time on my hands this Spring I am slowing it down pulling new growth in a prairie area we are trying to naturalize following the theory other taller prairie plants will eventually out-grow it. Because it spouts early and our beloved prairie typically is later ‘the creeper’ gets the early upper hand. Not this year in my yard, one possible benefit of Covid-19. Now I am worried about Squill too.

    • Hi Ralph, that Campanula is troublesome for us too! If you’re able to keep Siberian squill under control, that’s great. It is not on the invasive species in Minnesota yet, so no one is being forced to remove it. We are focusing on areas where it is taking over and preventing our desired plants from getting established. Glad you’re able to get out and work in your yard these days!

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