Spring is in the air, little green things are popping up all over, and we all heave a sigh of relief that the blanket of white stuff is finally gone. But beneath the snow that stopped everything in its tracks lurks a hardy, robust little puff of tiny green leaves that virtually grows before your eyes.
(This article was originally published on March 29, 2010. Your comments are welcome but please be aware that authors of previously published articles may not be able to respond to your questions or comments.)
Call it what you will – hairy bittercress, winter bittercress, hairy cress, popping cress – Cardamine hirsuta – is a weed that tries the most forgiving gardener’s patience. Growing worldwide (except in the Antarctic, this genus of the Brassicaceae family numbers more than 150 species, both annual and perennial. The plant is self-pollinating and in bloom throughout the year. It loves moist soil and grows aggressively under those conditions.
As the snow melts, tiny white, pink, or lavender flowers begin to appear. Yes, flowers. This tenacious weed is short-lived, which is good, you say. A life cycle of 6 weeks doesn’t seem like such a big deal. Think again – how many 6-week cycles are there in a year?
One of the biggest problems with bittercress is that, by the time you discover you have a problem, it’s almost too late to do anything about it. The first flowers appear in late February or early March, quickly form seed pods, and mature. If you touch those trigger-happy seed pods, i t’s all over – the pods explode, distributing seeds over an area up to 36 inches around each plant. Those seeds will germinate and begin sprouting with a few days and the cycle begins again, only over a larger area. Small to medium size plants produce about 600 seeds, and larger plants can yield up to 1,000 seeds.
Hairy bittercress is not invasive enough to warrant using herbicides. As soon as new plants appear in February or March, begin pulling them; these are the offspring of the previous fall’s seed crop. Through the season, always pull the seedlings when you see them; they have shallow roots and come away quite easily; however, bits of root left behind are capable of re-rooting under optimum conditions. The key is to get the plants before they set seed, which happens quickly after blooming. Eradicating this weed from large areas is almost impossible, unless you can hoe and remove. Keeping bittercress out of the flower beds is a little easier, but requires diligent hand-weeding to stay ahead of the seed formation. The leaves release a pungent aroma when bruised.
Hairy bittercress is a problem in greenhouses and nurseries, so be sure to clear off the top 2 to 3 inches of soil before planting anything you purchase. Scoop the soil into a plastic bag and dis card. Keep a close watch on newly planted containers, especially those that are positioned near flower beds. The propulsion factor of bittercress seeds can sneak new plants into your containers while you aren’t looking. Hairy bittercress is a real problem near flagstone patios or walks, brick work, or any hard-scaping that has space between the pieces. This weed does not need much to set down roots – even a small amount of sand between two bricks is plenty.
Hairy bittercress (Cardamine hirsuta) leafs out in a basal rosette, and like other members of the mustard family (Brassicaceae), its tender greens are edible. Don’t be fooled by the common name—its flavor is mild and peppery, not bitter. Though the flowers can be tough to chew, the tender leaves are suitable for a chic microgreens salad and have tons of vitamin C, calcium, magnesium, beta-carotene, and antioxidants.
The Weed of the Month series explores the ecology and history of the common wild plants that most gardeners consider weeds.
Though hairy bittercress is originally from Eurasia and was introduced to North America, there are several species of Cardamine that are native to the United States. Several are listed as threatened or endangered, mostly due to habitat loss.
More: Learn to identify more weeds and find out more about each one by browsing the Weed of the Month archive.
While urban grazers will be most focused on the leaves, I think the seed capsules are the best part of hairy bittercress. Called siliques, they look like purplish-green toothpicks standing upright around the flower. As the seeds mature, the pods begin to coil tightly until—pop! A gentle touch or passing breeze triggers the pods to explode and send the seeds flying as far as three feet from the mother plant. This ballistic dispersal strategy, known as ballochory, is also employed by jewelweed and cranesbill.
Severe infestations of hairy bittercress weed will require chemical treatment. Herbicides applied post emergence need to have two different active ingredients. The ingredients must be 2-4 D, triclopyr, clopyralid, dicamba, or MCPP. These are found in broadleaf herbicide preparations known as two, three, or four-way treatments.
Late winter and spring signal growth of all plants, but especially weeds. Annual weed seeds overwinter and then burst into growth towards the end of the season. Hairy bittercress weed is no exception. What is hairy bittercress? The plant is an annual weed, which is one of the earliest to sprout and form seeds. Control for hairy bittercress starts early in the season, before flowers turn to seed and get a chance to spread.
Prevent invasions into turf areas by encouraging good grass growth. The weeds easily infest thin or patchy areas. Apply several inches (8 cm.) of mulch around landscape plants to help prevent seeds from getting a foothold in your soil.
Cultural Control for Hairy Bittercress
Mowing will achieve control over time. Do it frequently enough that you remove the flower heads before they become seed pods.
Pulling out hairy bittercress weed usually leaves the root behind. The plant will re-sprout from healthy weeds and the problem persists. You can, however, use a long slim weeding tool to dig down and around the taproot and get all the plant material out of the ground.
The weed prefers cool, moist soil and is most prolific after early spring rains. The weeds spread quickly but their appearance reduces as temperatures increase. The plant has a long, deep taproot, which makes pulling them out manually ineffective. Control for hairy bittercress is cultural and chemical.
As temperatures get warmer, the plant will die naturally without having reproduced. That means fewer weeds the following season.