Many of us have spent time in the spring stooping to pull garlic mustard, Beverly Shores’ most hated plant. Garlic mustard has a new and unwelcome friend, dame’s rocket (Hesperis matronalis). You will see it blooming in our woods in late spring. It has pretty flowers ranging in colors from purple to white, but make no mistake—it is an invasive plant that is fast becoming a garlic-mustard-like threat.
Dame’s rocket and garlic mustard share many characteristics. Both are in the mustard family, both are biennials (meaning they live for two seasons—the first year obscurely as a leafy rosette at ground level and the second year blooming and producing abundant seed). Both have an elongated seed pod that splits open when ripe, known by botanists as a silique. When you see the dried stalks of dame’s rocket with the seed pod, you may even mistake it for garlic mustard. But dame’s rocket has oblong, sharply-toothed leaves while garlic mustard has heart-shaped, toothed leaves. Garlic mustard’s leaves reek of garlic when crushed but dame’s rocket offers fragrant flowers. Those flowers are the dead giveaway for identification. Large and in all shades of purple, pink and white, they have only four petals. Phlox, with which it is most commonly mistaken, has five petals.
Dame’s rocket has become widely distributed in woodlands because it is commonly added to so-called wildflower seed mixes. Look carefully on the label of such products for the name, Hesperis matronalis. It is also still sold by itself primarily in seed form by many horticultural suppliers despite its having been restricted or banned to varying degrees in several states. For example, in Wisconsin, it is “restricted—an invasive species that is already established in the state and has the potential to cause significant, environmental or economic harm or harm to human health.” Dame’s rocket has also been reported as invasive in a number of national parks, including the Indiana Dunes National Lakeshore.
Dame’s rocket is one of the easier invasive plants to control. Just pull it. With little effort, you can pull the second year flowering plant, as the first year rosettes are harder to locate. Like garlic mustard, you will need to bag it up and dispose of it because it can still form seeds if left lying. Also, just like garlic mustard, because of its seed bank you will need to pull it for several years to bring it into control.
There are many beautiful, showy native wildflowers that can be planted in woodlands for spring color. Most of these are available in nurseries, by mail order, or at local, native plant sales. To focus on some of the later season ones blooming in May, one can plant wild geranium (Geranium maculatum), wild columbine (Aquilegia canadensis), celandine poppy (make sure you get the native celandine, called Stylophorum diphyllum, with large, showy yellow flowers, and not the European Cheldonium majus, going by the same common name but with smaller flowers and an invasive habit), Virginia bluebell (Mertensia virginica), and woodland phlox (Phlox divaricata). These will also be good replacements if you are removing garlic mustard.
Vigilant homeowners in Beverly Shores can prevent the destruction of their woodland by removing oriental bittersweet. Because the understories contain a wide variety of vines, mostly native species, and some can look similar to bittersweet, the Environmenal Restoration Group (ERG) will be glad to help identify plants for you and make suggestions for removal and for native replacements. Don’t hesitate to contact Terry Bonace (email@example.com), Candice Smith (firstname.lastname@example.org), or Bill Schaudt (email@example.com) for assistance. Also, please visit our website at www.bserg.org for further information on invasive plants and native replacements.