weeds that pop seeds when touched

Weeds that pop seeds when touched

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.

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.

(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.)

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.

Weeds that pop seeds when touched

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.

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.

What is Hairy Bittercress?

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.

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.

Weeds that pop seeds when touched

Because Hairy Bittercress thrives in moist conditions and disturbed soil, it is also a pest in nurseries, and can be brought home via plant purchases. If you think that’s a problem for you, some cautious gardeners carefully remove the top inch or two of soil in the pots before planting. (If you do this, you should dispose of the scraped-off soil in your green can.)

Even if you didn’t recognize it outright, maybe you’ve had the experience of being out in the garden pulling winter weeds when you’re pulling what looks like a small “innocent” weed only to find it exploding seeds in your face and all over the nearby garden? The most likely culprit is Hairy Bittercress (Cardamine hirsuta), which starts growing almost immediately with the onset of the late winter rains. It originally looks like a small, flat rosette of small leaves and then in what seems like the next day, quickly produces small white, four-petal flowers on wiry green stems. Most of the problems with this weed can be “solved” if you pull it at this stage or at least before it flowers. Seemingly overnight, the flowers form needle-thin seed pods, which explode at the slightest touch, sending seeds in all directions (averaging around 600 seeds per plant… and the bigger the plant, even more seeds). Besides your garden, the seeds are easily propagated in cracks in flagstone, brick or concrete walkways.

Hairy Bittercress (Cardamine hirsuta)

I’ve become fascinated with this weed, at least so far. I’ve more-or-less got it under control in my garden. I really don’t remember it from years ago, but it sure has been a pest the last 5 years or so. Not a native of California, it is now here for the foreseeable future… and beyond. I can’t say it’s the worst weed in the garden, but it sure requires attention to keep it under control. Especially these days when it will be competing for available water.

If all else fails, Hairy Bittercress is a member of the mustard family and is edible, but you need to do your own research to find the right recipe to enjoy it (for an example, see http://www.eatingniagara.com/2013/04/weed-wednesday-make-that-hairy.html). To get ahead of its persistence in the garden, it’s definitely worth patrolling your garden for this weed once or twice a week during the winter and spring. It’s easy to hand pull when young. Once the seeds pop, you’ll be fighting a much bigger crop next year and it’s rare that herbicides would be considered appropriate for control in a home garden.

Another reason it’s my “favorite” weed? I still remember a fellow student in our Master Gardener class relating how she had “convinced” her young son to help weed the spring garden and he was complaining about the weed seeds popping in his face. She answered him by telling him to go in the house and get his safety goggles on and keep on weeding… something you might be considering adding to your gardening tools if you let Hairy Bittercress (Cardamine hirsuta) go to flower and reseed.