Dames Rocket – An Invasive Wildflower

Dames Rocket is a herbaceous biennial to short-lived perennial wildflower native to Europe, and very invasive in North America.  You’ve probably noticed it along roadsides in the United States though.  This flower is quite attractive and noticeable, as it often grows in thick stands.  During my morning commute in late Spring, I can see clusters of this plant for miles and miles when it is blooming.  I often notice this plant blooming at the same time as another invasive plant, Poison Hemlock.dames rocket invasive Hesperis matronalis

Dames Rocket Facts

  • Native to Eurasia
  • Has been introduced as an ornamental in North America, that easily escaped gardens
  • Is listed as a noxious weed in Colorado, Connecticut, and Massachusetts, and restricted in Wisconsin.
  • Is edible, and has been used medicinally in the past
  • Has been grown in gardens as an ornamental going back thousands of years
  • May emit a chemical that reduces or prevents germination and growth of native plants
  • This plant is hardy from zones 3-8.  Check your USDA garden zone here.
  • Is a member of the Mustard Family, just like another invasive species, garlic mustard

Scientific Name

The scientific name of Dames Rocket is Hesperis matronalis.

General Physical Description, Identification

Leaves/Plant

Dames Rocket grows 2-4 feet tall in good conditions.  The plant will have alternate leaves that are lance-shaped.  The size of the leaves are approximately 5-6″ long and 2″ at the widest part.  Normally there are no branches except where the flowers are located.Hesperis matronalis leaves bloom

Flower

The flowers will be concentrated at the top, each with its own branch.  The flowers will be clusters of small (1/4-1/2″ diameter) flowers with four petals each.  This is one of the distinguishing features of this plant, and the key for a quick identification when blooming.  Dames Rocket flowers have four petals, while our native Phlox flowers have five petals.  Additionally, the flowers really do have a pleasant smell.

Roots

The roots of this plant are short tap-root, and rough secondary roots.  It is quite easy to pull this plant when it is blooming, as the roots are pretty shallow.

Growing Conditions

Garden references will tell you that this plant likes partial shade and moist soil.  I’ve observed it in full sun on slopes, which would be more dry.  So, based on what I’ve seen I believe that his plant can grow in a variety of conditions.  The fact that it likes moist soil makes sense, since we see it bloom in May/June when the soil is still typically moist.

So, this would include both rich fertile soils along roadside creeks, to poor quality clay soils that are generally found in ditches (where I live).

If you wish to grow Dames Rocket……..

If you or a loved one are dead set on growing this pretty wildflower (that is highly invasive), then please make sure the seeds are controlled.  What I mean is that you should be snipping off the seed heads each year right after blooming, and make sure no others form.  You can sprinkle some seeds right where your current plant is blooming, and this will ensure you get more blooms the following year.  Also, if notice any random plants blooming the following year, please pull and dispose of them to keep your population contained.  Or better yet, just grow this plant in a pot.

Where you’ve probably seen Dames Rocket

It seems to really do well along roadsides and in ditches.  From approximately the middle of May through the middle of June I see this plant blooming prolifically.  It chokes out native plants by taking up the available real estate.  Since it grows up so fast in the Spring, it can shade out our native plants that may not grow as fast.  Since it drops so much seed, which germinates quite easily, it has become an extremely prolific species.

dames rocket colonies Hesperis matronalis
This roadside near a creek has been colonized by Dames Rocket

This plant is still sold in garden centers (in states where it isn’t listed as a noxious weed).  So, you may have noticed it in peoples flower gardens or containers.

How Dames Rocket Spreads

Seeds fall near the mother plant, and build up a seed bank.  Some of the seeds will germinate the following Spring, perpetuating the population.  In addition to this, the seeds can stick to the fur of passing mammals such as deer.  The seeds will eventually fall off the fur coats.  And given the proper conditions, will germinate and begin a new population.

Controlling Dames Rocket

This is a particularly difficult plant to control, just like Garlic Mustard.  You are really going to be fighting the seed bank, and new local populations that spring up.  But, persistence is the key.  The absolute most important factor in controlling the population is to make sure you kill the plant BEFORE seed pods form.  It may be possible that seeds can still become viable as pods dry, after being pulled, mowed, or sprayed.

Pulling Dames Rocket

You should pull every single plant when it is blooming, before seed pods have formed.  The roots are shallow and it is easy to remove.  However, try to pull it in wet conditions, as the roots will come out easier.  If pulled in dry soil, the stem will likely break off above the ground.  Then the plant may regrow and you will have to repeat the process.

If seed pods have already begun to form, then the plant should be burnt, or placed in a black plastic bag and left in the hot sun for a couple of days.  The heat should hopefully sterilize the seeds.  Then just label the bag as invasive plant, and set out for the garbage truck to pick it up.

Mowing

Mowing is not an effective means of control for Dames Rocket in most cases.  If mowed, the plant may regrow and form new flowers/seed pods.

Chemical

Herbicides will kill Dames Rocket.  The problem is, it is difficult to spray this plant without damaging other desirable native plants in the process.  Furthermore, if the seed pods have formed, the seeds may still be viable.  They could therefore fall and germinate, and you have to repeat the process the following year.

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