As I was outside soaking up the glorious October warmth and sunshine, I suddenly noticed little flecks of green scattered out in the landscape beds. Intrigued and forever curious, I wandered over, saw what was growing and I got a twitch in my eye. I remembered receiving an email from a reader telling me that I should remind everyone about seasonal timing and control of this despicable landscape curse. I wrote this Spring (April 23, 2021) in an attempt to stem the tide of the prolific green horde of wicked plants taking over the garden world…but of course, they have returned! This vile weed belongs to the mustard family (Brassicaceae) and is commonly known as Hairy Bittercress (HB) or Cardamine hirsuta.
Like a true winter annual weed, HB germinates and leaf’s out as a basal rosette to sneakily and vegetatively pass through winter, harvesting and using any available sunshine. In early Spring, the frilly, yet tidy green mound sends up flower stalks with tiny, white flowers to begin to create the real mess… pods full of seeds! Each plant has the potential to produce 600 to 1,000 little green bombs called seeds!
But the salient message in this moment is… NOW IS THE TIME TO CONTROL THIS GREEN MONSTER!! This annoying plant scourge of the landscape can now be managed using a combination of different types of herbicides. Since it has recently germinated, the seedling is very tender and has not established an extensive root system yet; therefore, it is very sensitive and susceptible to ANY disruption or disturbance.
IMMEDIATELY assault the green bombers using a non-selective postemergence herbicide that is a contact, foliar-applied, cellular membrane disruptor. For example, products like pelargonic acid (Scythe®), potassium or ammoniated soaps of fatty acids (FiNALSAN®, BioSafe Weed & Grass Killer®, etc.), citrus oil (Avenger®), vinegar ≥ 20% acetic acid (WeedPharm®) or any combination of these oils (AllDown®) are also known as “burndown” herbicides. These products will do a great job wiping out those tender, green seedlings of grief, impacting only the plants they are directly sprayed on… but they will have NO IMPACT whatsoever on seeds!
So, in order to achieve successful control of the plague of HB, preemergence herbicides are needed to inhibit any new seed germination and must also be applied NOW. Don’t hesitate to apply a preemergence herbicide, like trifluralin (e.g. Preen®) or whatever is your preferred or favorite weed preventing product, and ACTIVATE IT! To activate preemergence herbicides, one simply needs to spread the chemical out uniformly into the top layer of soil. This is usually achieved applying about one-quarter to one-half an inch of water (irrigation), to create that chemical barrier!
Remember to remain ahead of this seed flinging machine, don’t let those HB plants flower or mature to develop those blasted seed pod launchers! Keep after any escaped germinating seedlings until the preemergence herbicide kicks into gear. And even then, keep on your guard for the emergence of any member of the hairy green horde and shamelessly “BATTLE THE BITTERCRESS”!