My Favorite Weed.... NOT!!!

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.

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.

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.)

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.

Steve Morse
Contra Costa Master Gardener