Good Oak News

Wednesday, May 23, 2012

Dames Rocket: The Overdressed Matron

We're seeing a lot of pink outside these days. On roadsides, railroad corridors, degraded woodlands, stream corridors, backyards... seems like these showy pink flowers are everywhere.
Only a few blocks from my home I found this massive colony of Dames Rocket, likely there's one not far from your home too.


The flower in question is dames rocket (Hesperis matronalis) and though it is admittedly showy, it is indeed an aggressive invasive plant. Dick Young, the author of my favorite plant book, Kane County Wild Plants and Natural Areas, describes them as such:
[Found] in shady waste areas and disturbed waysides, crowding out and becoming exclusive stands. This popular Eurpean perennial is an escaped garden plant that is still sold in wildflower mixes. It has striking white, pink and lavender blossom clusters from mid-May through July that are commonly confused with Phlox. Their pervasive fragrance and gaudy color suggests an overdressed matron wearing too much cheap perfume, as these plants often become too much in the landscape. [emphasis added]
I have always had a great fondness for Mr. Young's colorful and accurate descriptions of wild plants!

Identification:

dames rocket

Many people confuse this species with our native phloxes. But dames rocket, like all members of the mustard family, has only 4 petals. Any phlox, will have 5 petals. Count them: P-H-L-O-X, 1-2-3-4-5, petals.
prairie phlox (Phlox pilosa)
woodland phlox (Phlox diviricata)
Superficially similar yes. But there are many clear differences. For example, dames rocket is typically 3-4' tall. Our native phloxes rarely, if ever grow taller than 2'. Also, phloxes have small, rather slender leaves that are arranged opposite of each other on the stem. Dames rocket has large leaves which are arranged alternately on the stem (one will be on the left, then up a few inches the next leaf will be on the right, and so on). See below: 
More dames rocket.

Elimination:

Its important to note these differences, because dames rocket is an aggressive weed that should be eradicated. I know it's pretty to look at, but in the long term allowing it to persist will lead to disaster. I was at a property this spring where the owner had worked hard for a decade controlling dames rocket's better known cousin, garlic mustard but they had left the dames rocket alone. It got so thick that last year's dead stems were like corn stalks in a field, and there were very few native plants left in the area. Once you know what a terror they can be in a natural area, they seem considerably less attractive.
Dames rocket is a short-lived perennial. They spread more slowly than garlic mustard, but they live and flower for a couple years (as opposed to garlic mustard which flowers only once before it dies), which means that over the life-time of a single plant it will produce as many, maybe more seeds than a garlic mustard plant will produce. They overwinter as rosettes. These ground-hugging basal leaves are variable and can be difficult to identify at first; sometimes they look like dandelions, sometimes like common evening primrose, sometimes like penstemons.
Dames rocket as an overwintering rosette.

Our Weed Identification and Control Sheet about dames rocket discusses control methods in detail, but let me give you a few tips: The first is to spray or dig them out in the winter months. As long as the ground is not frozen and it's above 35° F, these plants are actively photosynthesizing, meaning they can also absorb herbicide. It's easy and relatively safe to do when all of your other plants are dormant. Another tip I have is to dig/pull them out just after they finished flowering. That way, you and your neighbors can enjoy the pretty flowers this year, but you can eliminate them before they can create any seeds. Be sure to bag these plants and dispose of them in the trash so they can go to the landfill, not the compost pile!

Alternatives:

So what can you plant if you want some attractive, showy flowers in late spring? Fortunately, there are lots of native alternatives. Here are three that are hardy, can tolerate shade and sun, and are pretty showy:

Wild Geranium (Geranium maculatum): Happy in full shade to full sun, lovely pink flowers.



Wild Columbine (Aquilegia canadensis): Delicate red flowers attract humming birds, full sun to moderate shade.



Golden Alexanders (Zizea aurea): Yellow flowers, good in moderate shade to full sun. Larval host to black swallow tail butterflies. Can be somewhat tall and aggressive in a home landscape.

(with geranium in the foreground)

Prairie phlox and woodland phlox (seen in above photos), for sun and shade respectively, are also good alternatives to dames rocket. They are quite colorful, but a bit smaller. They tend to get lost among taller plants, and are best used along edges or in more manicured native perennial gardens.