Posted on

weeds that throw seeds when touched

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.

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.)

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.

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.

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?

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.

This pesky weed is small enough to hide among your landscape plants. Its extensive seed expulsion means that just one or two weeds can spread quickly through the garden in spring. Early control for hairy bittergrass is essential to protect the rest of the landscape from an infestation.

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.

Its small white flowers are similar to those of chickweed, another ‘unwanted plant’ that blooms early in the Spring. But chickweed is more of a flat, spreading, mat-like plant. And its seedpods aren’t faster than a speeding bullet. Both weeds are remarkably easy to control in flowerbeds; just pull them, roots and all, out of wet soil. Chickweed comes out in big clumps, while bitter cress has a nice little stalk that gives you a handle to grab onto. Just remember to soak the soil first; all weeds come out of wet soil MUCH easier than dry.

If you scalp the lawn, weeds will thrive. If you water it frequently for short periods of time, weeds will thrive. And if you feed the poor heat-stressed thing in summer, weeds will take over.

Both weeds are also highly edible, especially when young. Chickweed is more nutritious than the salad greens that many people remove it to plant! And, although hairy bittercress (a member of the mustard family) doesn’t have nearly as many wild food fans as chickweed or purslane (perhaps the most edible ‘weed’), it does have some of the peppery taste of its namesake watercress, and it’s loaded with cancer-fighting nutrients. Pick it before the flower buds form and it won’t have nearly as much of the bitter edge that older plants take on. (Flowering changes the flavor of virtually all herbs and greens for the worse.)

If I don’t get to them in time, I toast the seedheads with my trusty flame weeder before I pull the plants, just like I do with dandelions that have progressed to the puffball stage. Dandelion seeds burst into little flares of color—like Munchkin fireworks. Bittercress seeds explode with a loud ‘pop’. (Organic gardening is SO much more fun than spraying hormonal disruptor around!)

If I’m paying attention and life cooperates, I’ll pull the weeds while they’re still in flower and before they set seed. Both weeds get composted—mixed into a good amount of shredded leaves hoarded from the previous fall; at least two parts leaves to every part green weed. The bitter cress typically comes up with a good amount of soil attached to its roots, which adds microbial life to the pile; and the chickweed has a lot of water content to help keep the moistness levels right.