It’s the very beginning of June in Connecticut.  Since mid May or so, gorgeous patches of pink, purple and white ‘wildflowers’ have appeared along roadsides.  A few years ago, my mom was visiting from Michigan around this time for a graduation.  She has been an avid gardener for many years and when she saw these flowers, she exclaimed, “oh, those wild phlox are just beautiful!”   So even a seasoned gardener can mistake this invasive plant, Dame’s rocket (Hesperis matronalis) for wild or garden phlox.

DamesRocket.GarlicMustardJAllen  J. Allen photo

Relatively speaking, Dame’s rocket (other common names include dame’s violet and mother-of-the-evening) is a newcomer to the status of invasive plant so its impacts on native species are not well studied.  It is known that it effectively forms monocultures where it has escaped from cultivation, is a prolific seed producer, and is not kept in check by pests or diseases in North America.  It is still readily available as seed commercially but is banned as an invasive in some states including Connecticut and Massachusetts. This means it cannot be bought, sold, cultivated or moved within these areas.   Unfortunately, it is still commonly included in ‘wildflower’ seed mixes for gardens in other parts of the United States.  According to a USDA distribution map, it is found throughout the continental U.S. except for the most southern parts and much of Canada.

Where did it come from?  It was introduced as an ornamental from Eurasia in the early 1600s so it’s had plenty of time to become established.  Dame’s rocket is in the plant family Brassicaceae so is related to the mustards, cabbage, broccoli, kale, etc.  The leaves, oil and seeds are edible and the plant is cultivated for its oil which is used in perfumes. Young leaves are a good source of vitamin C and they can be used in salads.  Speaking of perfume, it’s reported that the flowers of this plant produce a stronger scent in the evening.

DamesRocketLeavesJAllenDamesRocketFlowersJAllen J. Allen photos

Characteristics that can help identify Dame’s rocket include branched clusters of white, pink, and purple flowers that are about 3/4-1″ across and have four petals.  True phlox flowers have five petals. In addition, true phlox (wild) flower later in the season.  The leaves of Dame’s rocket are alternate, lance shaped and have serrated or toothed edges as shown above. In addition, leaves (except for the lowest on the stem) are directly attached to the stem and have no petioles. In contrast, true phlox have opposite leaves.  I’ll pop in a photo of true phlox below so you can see the leaves and flowers together.

 Wild blue or woodland phlox (Phlox divaricatahttps://en.wikipedia.org photo. This species is native to eastern North America.

Another distinctive feature of Dame’s rocket is the long, spindly seed pod (silique).  These form from the bottom of the flower cluster upward, so the youngest flowers (formed over a 4-6 week period) are at the tops and produce seed pods last.  Seeds and pods mature over the summer and when dry they split open releasing seeds into the soil.  Some are eaten by birds allowing for longer distance dispersal.  Each plant can produce hundreds of seeds which can remain viable in the soil for many years.

Dame’s rocket seed pods (siliques) on the left (Mark Frey, The Presidio Trust , Bugwood.org.  First year rosette on the right (Leslie J. Mehrhoff, University of Connecticut, Bugwood.org).

This plant is considered a biennial or short term perennial.  The first season of growth from seed produces a low-growing rosette of leaves which survive and remain green through the first winter.  The next season a 2-4′ flower stalk is produced as shown above.  This will dieback in the fall and some plants will produce new flower stalks in the third year.   The plant appears perennial where established in part due to the large seed supply that is produced annually.

It’s hard to want to destroy such a beautiful plant but if removal is required the methods include mechanical (pulling), burning, or herbicide applications (useful for large populations).  The best time to pull plants is in spring before seed pods mature.  Seeds can still ripen on plants pulled at this time using nutrients from the stems and leaves so for effective eradication, bag or burn the plants and remove them.  If not feasible, pile the plants in the center of the area where there is likely to be a lot of seed in the soil already.  The pile can be covered with black plastic to heat the pile and kill some of the plants.  A good approach for herbicide use is to apply to rosettes in early spring or fall to avoid injuring desirable plants nearby.  In early spring they will not have germinated yet.  Temperatures should be at or above 50 degrees Fahrenheit.

J. Allen