“I know that Dame’s rocket is technically an invasive exotic, but I love this plant. Despite being labeled an exotic, they have also long been a staple of American gardens – an heirloom species from the nineteenth century. So, while not native, they’re traditional.”
– Found on an Internet gardening site.
This comment illustrates a problem: the invasive plants that are the most difficult to convince people not to plant are those that are attractive and easy to grow, especially if they have fond memories of them growing in Grandma’s garden. Dame’s rocket is in that category.
If you don’t recognize the name dame’s rocket, you may be familiar with some of its other monikers: dame rocket, sweet rocket, dame’s violet, mother-of-the-evening, damask violet, dames-wort, dame’s gilliflower, night scented gilliflower, queen’s gilliflower, rouge’s gilliflower, winter gilliflower, summer lilac, or wild phlox. These common names all refer to the same plant, Hesperis matronalis. “Hesperis” comes from the Greek word for evening, and the name was probably given because its flowers are most fragrant in the evening.
A tradition for hundreds of years
Although it indeed has been a “traditional” plant since the sixteen hundreds, when it was introduced to this continent, dame’s rocket is native to Europe, and east to Siberia. The only states free of this plant are Hawaii, Arizona, Texas, Oklahoma, Louisiana, Alabama, Mississippi, South Carolina, and Florida, though it has not reached invasive status in all the remaining states. It’s also found in all but a few Canadian provinces.
Dame’s rocket acts like garlic mustard, but looks like phlox. Both traits are unfortunate. Botanically, dame’s rocket, like garlic mustard (Alliaria petiolata), is in the mustard family. They both are biennials, producing a rosette of leaves the first year, flowering the next, and producing huge numbers of seeds. Like garlic mustard, it prefers moist, well-drained soil in partial shade, but will also grow in full sun.
That dame’s rocket looks like the beautiful native phlox (Phlox spp.), accounts for its popularity. Like phlox, its colors range from white to shades of pink and purple. It’s easily distinguished from phlox, though, because, like garlic mustard, the flowers have four petals, not five as does phlox. Their leaves are different, too. The leaves of dame’s rocket are sharply toothed and alternate – the leaves of phlox are smooth and opposite.
Perceptions and misperceptions abound
Another misleading comment found on an Internet garden site: “This plant is a common wildflower here in the Catskills. It grows by roadsides, ponds, in meadows, etc., and self seeds into stunning colonies. I have some in semi shade in my wild garden where it self seeds nicely in wet clay soil, and competes with grasses, asters, and goldenrod quite successfully.”
Unfortunately, this comment is true. But that it successfully competes with native plants such as grasses, asters, and goldenrod isn’t good news for wildlife or for native plant communities. And it’s increasingly moving into forests where it can shade out native wildflowers.
Sold by seed companies and nurseries
One reason for the dame’s rocket’s success is that it’s recommended and sold by seed companies and nurseries, and is frequently found in wildflower mixes sold for “naturalizing.”
For example, here are some recommendations found on the Internet: “Excellent plant for meadows, naturalized areas, or cottage gardens.” And, “They are best used for naturalizing on slopes and in woodland areas.”
And even while noting its invasive tendencies, some universities and botanical gardens nevertheless provide information on growing it.
Controlling dame’s rocket
Control is similar to the procedures used for garlic mustard. Pull the plants out, taking care to get the roots to prevent resprouting. Be sure to remove the plant before it sets seed. As with garlic mustard, seeds remain in the soil for many years, so pulling new seedlings is a multi-year task until the seed bank is exhausted. As with garlic mustard, a general herbicide like glyphosate is effective, but use the usual precautions.
If the plants are in bloom, don’t compost them, as the seeds may still ripen and spread. Flower heads should be bagged for landfill, or dried and burned where permitted.
Still attached to your dame’s rocket? Keep them in your yard by removing the flower stalk when the flowers begin fading, so no seed pods form. But better yet, consider planting some of the beautiful native alternatives instead.