Hairy Bittercress – A prolific winter weed


Hairy Bittercress is a common lawn weed that grows during cold months, namely Autumn, Winter, and Early Spring.  Known as a winter weed, Hairy Bittercress is an annual in most climates.  During winter months you can easily identify it by the small basal rosette (cluster) of leaves on the ground.  It can become very prolific in a short time, filling in gaps within your normal grass.  In my community, we went from never seeing this weed to it spreading out in all of our yards in one season (at least it seemed that way).  If your yard has areas that suffer from other weeds, as they die out in the winter Hairy Bittercress can easily move in.

An infestation in my yard, where we have very thin grass. There are dozens of new seedlings……..

 Hairy Bittercress Facts

  • Seeds from Hairy Bittercress germinate when the soil temperature is cool
  • Research suggests that the seeds will not germinate in high temperatures.  It is almost that the plant requires a ‘summer’ stratification.
  • Native to Europe and Asia, it has become established all over the world
  • Seed capsules will ‘explode’ when ripe, throwing the seed up in the immediate area
  • The plant goes dormant once the temperatures warm up, and you will not see it again until Fall
  • The Scientific Name of Hairy Bittercress is Cardamine hirsuta
  • Hairy Bittercress is a member of the mustard family

Hairy Bittercress Physical Description

New plants will germinate in later Fall, around November to December.  They will slowly grow over winter.  They will initially be a small basal of leaves several inches in diameter.  In spring, the plant will send up stalks about 6″ tall, and will regrow them after mowing.

Stalk / Stem

A short stalk, 3-10″ tall will grow from the center of the rosette, and have several stems/branches that produce flowers at the top.  The stalk will be light green in color and will develop in Early Spring.

Leaves

Basal leaves will grow upwards of 6-8″ diameter (15-20 cm).  The Basal will stay very low to the ground, 1/2″ (10 mm) height.  Individual basal leaflets are kind round.  Eventually there will be several leaves on the stalk in the spring, but these will be long and slender (but still rounded).

hairy bittercress basal rosette
Hairy Bittercress basal rosette of leaves during a warm day in January.
hairy bittercress leaves
Some Hairy Bittercress plants before flowering. This basal rosette of leaves make it easy to identify Hairy Bittercress in late Winter.

Flower

Individual flowers are very small, only 1/4″ (6 mm) diameter.  The flowers are white and have four petals each.  Blooming will last approximately one month.

hairy bittercress flower
The teeny tiny flower of Hairy Bittercress

Root

Hairy Bittercress roots are fibrous and shallow.  This makes it somewhat easy to pull when the ground is moist.

Hairy Bittercress Lifecycle

Hairy Bittercress is a winter weed.  Its life cycle is almost the opposite of most plants.  Let me explain – in general we think of seeds germinating in the Spring, growing, flowering – and dying off in the winter.  Many types of seeds won’t germinate until they have spent the whole winter outside.  Well, Hairy Bittercress seeds will not germinate in warm temperatures.  There are studies suggesting that the seeds have a germination inhibitor during warmer temperatures, which matches my personal observations of Hairy Bittercress.

So, we will have germination of seeds in bare spots of your yard, or if your lawn is mowed very short.  The seeds need sunlight to germinate.  There will be slow growth throughout the fall-winter-spring.  This will culminate with stalks arising in Spring, and flowering in mid-Spring.

Exploding Seed Capsules!

Seed capsules will form, and when ripe they will burst.  Seed will be dispersed up to 15 feet (5 meters) away from the plant!  How does the plant do this?  Nobody is truly sure, but there are a couple of possibilities.  One theory is that as the outer layer/leaf material of the capsule dries, it shrinks.  This shrinkage creates tension on the membrane until…Pop!  The seed flies out.  The other theory is that as the seed dries the plant adds water to the base material/membrane, causing an increase in pressure/stress to the outer layer of the capsule.  This occurs until…..Pop again!  The bottom line is that the seeds can fly far and wide from this plant!

The life cycle of Hairy Bittercress in my yard

I generally see new seedlings in November in bare spots of my yard.  They will slowly grow over winter (on warmer days).  Eventually sending up stalks and flowering in March/April.  And usually, once temperatures have warmed up, Hairy Bittercress will go dormant and disappear.  This generally happens by the time I’ve mowed my lawn twice.Cardamine hirsuta

Growing Conditions

Hairy Bittercress prefers moist soil (soil is generally moist during cooler months), and partial to full sunlight.  It is quite versatile though, as when I first noticed this plant it was seemingly everywhere.  Even in shadier spots of my yard.

How to Control Hairy Bittercress

Prevention

The best method of control for Hairy Bittercress is to not allow it to become established.  If you notice individual plants, go pull them.  You must do this before it goes to seed.  So, small infestations must be handled quite quickly.

Also, don’t mow your grass too short.  The seeds need sunlight to germinate, so having a lawn that is 3″ tall (7-8 cm) can prevent seeds from germinating.  Additionally, keeping your lawn thick and healthy will stop any bare patches or spots, which the seeds need to germinate.

Mechanical

Pull small patches and individual plants when noticed.  This is very important to prevent a complete infestation.

Chemical

Common broadleaf herbicides are effective for controlling Hairy Bittercress.  Apply the herbicide in early Spring, while the plant is sending up stalks.  Just take care to only spot treat this plant to minimize the impact that chemicals can have on soil life.

Fauna

Although Hairy Bittercress is invasive, it does add a small benefit to wildlife.  Butterflys do visit/pollinate the flowers in the Spring.  Particularly the Sping Azure butterfly.

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Invasive Plants

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Joe Foster

Hi - I grew up outdoors in nature - hiking, fishing, hunting. In high school I got my first job at a garden center where I learned to garden and landscape. I've been growing plants from seed and designing native plant gardens for over six years. I hope to share some of my knowledge with you! Additionally I am a wood worker / DIY enthusiast. I enjoy designing/building projects (with hand tools when I can!). I hope to give you some tips and useful information!

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