Hairy Bittercress Busting!

Published on

How many of us have gone outside to smugly look at our gardens that looked pristine and in excellent shape heading into the winter?  Then in the Spring, as we emerge from our winter hibernation to survey our domain… We are shocked!  What the heck happened out there because there are tufts of green weeds everywhere!  A gardening friend asked me what this green thing was, because he had already pulled or dug up two wheelbarrow loads of them!  The prolific green demon belongs to the mustard family (Brassicaceae) and is known as Hairy Bittercress (HB) or Cardamine hirsuta.


Hairy Bittercress in landscape bed
Hairy Bittercress, Cardamine hirsuta, in landscape bed


HB is typically a winter annual, but it can also be a summer annual and or even act as a biennial—another plant that doesn’t follow the rules!  As a winter annual, HB germinates and leaf's out as a basal rosette to sneakily and vegetatively pass through winter, soaking up any available sunshine.  In early Spring, the tidy green mound sends up flower stalks with tiny, white flowers to begin to create the real mess… seeds.  Each plant has the potential to produce 600 to 1,000 little green bombs called seeds!


Hairy Bittercress with flowers and seed pods
Hairy Bittercress, Cardamine hirsuta, with flowers and ripening seed pods called siliques


The flowers form thin, purple, seed pods, which are actually called siliques.  This is where HB disguises itself as innocuous and cute with the upright, purplish-green siliques scattered around the flowers, looking so Spring-fresh and nice.  As the seeds mature inside of the siliques, these prolific pods begin to coil tightly to create the greatest gardening crime ever—they explode, flinging seeds in all directions!


Hairy Bittercress with ripe seed pods
Hairy Bittercress, Cardamine hirsuta, with ripened purple seed pods


Well okay, they don’t really explode, but the tension in the ripe silique causes it to suddenly split apart (dehisce), catapulting seeds in every direction.  Anything barely touching the nasty pods, like tools, your hands or even the gentle wind stirring through the pods, causes a reaction.  The appalling purple silique will violently detonate, whipping the seeds up and out into the blast zone, to sail as far away as sixteen feet!  When you weed, they get in your eyes, up your nose, and in your ears and hair—they are everywhere!!


Hairy Bittercress loaded with ripe seed pods
Hairy Bittercress, Cardamine hirsuta, loaded with ripe siliques ready to split open and scatter seeds


This obnoxious weed can be controlled with various preemergence and postemergence herbicides, but it is all about application timing.  Usually late in the year, you are satisfied with the garden season and have put most garden chores and tasks to bed, ready for winter.  That is the prime time to become a bound and determined bittercress buster!


Hairy Bittercress, Cardamine hirsuta
Hairy Bittercress, Cardamine hirsuta, already loaded with seed pods


To achieve successful control of hairy bittercress, preemergence herbicides applications should be applied in late summer or early fall.  Postemergence herbicides applications, using a contact, non-selective herbicide to target tender seedlings, should begin in mid-fall or early Spring.  To get ahead of this seed flinging machine, don’t let it flower or mature to develop those blasted purple launch pods!  Keep after those tender, germinating seedlings, which shamelessly seem to emerge year-round, with no hesitation whatsoever.  Therefore, anytime you get a chance to go outside when the weather warms up… Get outside and begin BUSTING HAIRY BITTERCRESS!