Gardening Tips: Asparagus Patch Weeds and Purple Roadside Flowers

By Vijai Pandian, Horticulture Educator, UW-Madison Extension Milwaukee County

Dame's Rocket flowers have four petals that are pinkish-purple to white.

Dame’s Rocket is a highly invasive plant that can quickly displace other native vegetation. To successfully manage Dame’s Rocket, cut or mow the flower hears immediately after it’s done blooming to prevent seed formation.

What’s the phlox like plant with its purple bloom along the roadsides?

With its attractive purple- pinkish to white fragrant flowers, Dame’s Rocket (Hesperis matronalis) is a highly invasive plant that can quickly displace the native vegetation along roadside ditches, wooded and open areas.  Dame’s Rocket is commonly visible in its peak blooming stage from late spring to early summer and can be confused with garden Phlox due to its similar flower color. However the two species has few distinguished characteristics like the Garden Phlox has five petals whereas Dame’s Rocket has 4 petals and the leaves of Garden Phlox are opposite, non-serrated whereas Dame’s Rocket has alternative and serrated leaves.

Dame’s Rocket lives about 2 to 3 years and reproduces by seeds during its second or third year of growth. To successfully manage Dame’s Rocket, it is important to cut or mow the flower head immediately after its done blooming to prevent the seed formation. Hand pulling and bagging the plant for landfill disposal can be effective on small areas. To learn more about Dames’ Rocket and other invasive plants, visit


How to control weeds in asparagus patch?

Weed control in asparagus should be started early in the season before the weeds emerge in the bed. Organic pre-emergent herbicides like corn-gluten meal can be applied in the spring (too late to apply now) to prevent the germination of the weeds.  Hand hoeing or shallow cultivation (no deeper than 2-3 inches) using a rototiller between the rows can help in keeping the weeds under control.  Mulching to a depth of 3-4 inches around the plant can prevent and smother the weeds. Spot treatment with Roundup can be sprayed immediately after the last harvest of all spears on the emerged broad-leaved and grassy weeds, but make sure the herbicide does not get in contact with the ferns or spears.  Grassy weeds in the patch can be controlled by using a selective herbicide like Poast. It should be sprayed on actively growing grass and should not be applied more than twice in the season.  Read the product label for safety and instruction.

One of the popular misconceptions to control garden weeds is the use of salt. Though salt can provide some weed control without harming asparagus, it will ruin the structure of the soil due to the sodium content. Salt can eventually kill the asparagus plant and can leach into nearby garden soil and destroy desired crops.  Sodium in the salt displaces the other nutrients from binding the soil and can cause poor water penetration. Do not apply salt in your garden.


For more gardening info, contact:

Extension Milwaukee County – 414-615-0515, email: