That's Invasive? European Bellflower ~ Campanula rapunculoides
Native to: Eurasia, introduced as a garden ornamental
Best Method of Removal: Dig Out Plant & Taproots
Interim Measures: Remove flower stalks to prevent seed production until you can dig plants out
Native Alternatives: Campanula americana (Tall Bellflower), Campanula rotundifolia (Harebell)
As this first photo shows, European Bellflower has attractive blue-violet, 5 petaled bell shaped flowers that alternate up the 3 - 4 foot flower stalk. The leaves are serrated and very look very similar to violet leaves with a broad base narrowing to a tip.
I have seen extensive patches of this plant in the Twin Cities metro area, in small South Minneapolis lots in full sun and growing in part shade in suburban park woodlands.
Depending on the age of the plant, the tap root varies in depth. Many of the plants I dug in my yard had tap roots that were 18 inches below the soil surface. From these taproots were tiny strands that snaked their way to the soil surface. From these strands a clump of leaves arises, and from this clump the plant sends up the flower stalks in late June to early July.
If you attempt to apply a herbicide like RoundUp® on this plant, it is relatively ineffective because it may kill off the leaves on the surface but the reserves that remain in the taproot will allow the plant to send up new clumps of leaves.
I have smothered some clumps in my yard with some success. I applied a thick layer of paper and 4 to 5 inches of mulch. This does not eradicate the taproot, the foliage will disappear for several years until the paper and mulch break down. The taproot then sends up more strands to reestablish leaf clumps on the soil surface. These leaf clumps are often very small, distorted and weakened. If you continue to smother or pull these clumps, the tap root will eventually die off after depleting its reserves, just keep in mind this is a long term process.
If you find this plant for sale at your local nursery, be sure to inform the manager that it is invasive and they should not continue to offer it for sale!
Link to Invasive Plant Atlas Distribution Map
Link to USDA Plant Database Distribution Map
© Heather Holm, 2015. Heather Holm