seed popping weeds

Seed popping weeds

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.

Hairy Bittercress (Cardamine hirsuta)

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.)

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.

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.

Seed popping weeds

When the seedpods are ripe the seeds are dispersed explosively for up to 1 m if the plants are shaken by the wind or by weeding operations. The seeds become sticky when wet and can be spread on tools and clothing.

Hairy bittercress is variable in size and leaf shape. Waved bittercress, C. flexuosa, closely resembles hairy bittercress and is also variable in habit. It is usually annual or biennial but occasionally perennial. A related introduced weed, New Zealand bittercress, C. corymbosa, has become troublesome in polytunnels. It is similar in appearance to hairy bittercress and has the same explosive seedpods but is generally smaller.

There is little germination of the fresh seeds. The seed after-ripens at high temperatures. The higher the temperature the greater the temperature range at which subsequent germination will take place. Germination is increased by a period of dry storage.

Hairy bittercress seed germinates from April to December. There are peak flushes of seedling emergence from July to August and November to December but this varies in different years. Autumn is the main period of seedling emergence. Hairy bittercress can complete its lifecycle in 5-6 weeks. The cycle is longer in rich soils and shorter in poor ones. Seedlings can survive the severest frost.

A native, annual to biennial plant found in open and cultivated ground, and on rocks and walls throughout the UK. Hairy bittercress is recorded up to 3,800 ft. It is a common weed of gardens, greenhouses, paths, railways and waste ground. It is a particular problem in container-raised plants from nurseries and garden centres.

Hairy bittercress is found in flower all through the year but mainly from March to August. It is automatically self-pollinated. Seed is shed in May and June and sometimes into the autumn. There are around 20 seeds per seedpod. The average seed number per plant is 600 but a large plant may yield several thousand seeds. Plants can be found in fruit for 8 months of the year.

Hairy bittercress forms a relatively persistent soil seedbank.

Seedlings should be killed by early cultivations and regular hoeing to prevent hairy bittercress plants flowering and setting seed. Stem fragments are capable of re-rooting following cultivation in moist conditions. Hairy bittercress seedlings should be removed from container plants before the weed can set and shed seeds. The standing areas must also be kept weed-free. Improved drainage may discourage this moisture-loving weed.