(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.
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.
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.
Mowing will achieve control over time. Do it frequently enough that you remove the flower heads before they become seed pods.
Hairy bittercress weed (Cardamine hirsuta) is an annual spring or winter pest. The plant springs from a basal rosette and bears 3 to 9 inch (8-23 cm.) long stems. The leaves are alternate and slightly scalloped with the largest at the base of the plant. Tiny white flowers develop at the ends of the stems and then turn into long seedpods. These pods split open explosively when ripe and fling seeds out into the environment.
Cultural Control for Hairy Bittercress
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.
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.
As a self-seeding annual weed, these plants germinate from seed, form a plant that forms flowers and then seeds. When the seeds are spent, the original plant dies. (There are some perennial forms of Cardamine as well, fyi). And, the plant doesn’t form a deep taproot like you’ll find with Dandelions and Dockweeds. Instead, it is fairly shallow-rooted, with wide tiny roots that are easy to pull. It does have a slight taproot, but nothing difficult to remove. Plus, unlike the taproot weeds, if you don’t get all of the root from a shotweed plant, it isn’t likely to grow back (or multiply) from the roots.
Shotweed Rosette Flowering
One of the many things I do as a garden coach is teach individuals about the weeds in their gardens. Knowing what a weed is and how it grows helps us understand the best ways to deal with the plant. Today, I begin a garden weed blog series, Weeds in Seattle, with a tenacious little plant – Shotweed (Cardamine oligosperma).
As soon as you see shotweed, pull it!
Well, shame on me. Letting those pretty little white flowers form and go to seed just meant I was letting this weed get the best of my garden spaces. Sure, we all have to pick our battles in the garden, and we do what we can to stay on top of everything, but knowing that this is a fairly simple weed to remove means I’m going to encourage you to work at keeping it at bay.
Shotweed Seeds Ripening
It is important to dispose of the pulled plants and not just set them back on the soil. If you pull them and set them down, even root side up, these buggers often have the ability to reroot themselves. Probably this is because they grow in cool, moist weather that can give exposed roots a fighting chance even will removed from the ground.
Shotweed seems innocuous until it takes over the garden. I recall in years past telling a neighbor, “As far as weeds go, this one isn’t too horrible. See it has pretty little white flowers.”