What Is Hairy Bittercress?

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Hairy bittercress (Cardamine hirsuta) is a one-of-a-kind lawn weed that is unmistakable once you know how to spot it in your lawn. This broadleaf weed spreads unique flowers and leaves across your landscape that harm your grass and plants by stealing nutrients from the soil, but that is not where the dangers stop. Come learn how dangerous hairy bittercress can be to your landscape and what you can do to stop it

Identifying Hairy Bittercress

Hairy bittercress is a small and distinctive-looking weed that is commonly found in various habitats, including woodlands, gardens, and lawns. It is easily recognized by its basal rosette of leaves and upright stems that branch off in multiple places. The leaves are round or oval, and they alternate along the length of the stems. The leaflets are typically roundish and hairy, and the stalk may be somewhat hairy, but not always.

The plant is most easily recognized by its tiny white flowers that are about 2.5 to 5 mm long, with four petals that bloom in clusters near the top of the stems. These types of flowers are characteristic of the mustard family (Brassicaceae), to which hairy bittercress belongs. The plant also produces seed pods along the upper stems that are known to occasionally “shoot” out seeds in a flicking manner, which will spread the invasion across your property. 

Key Characteristics

  • Tiny White Flowers: Bittercress is known for its small white flowers that form in clusters at the ends of its stems.
  • Fine Hairs: Hairy bittercress leaves are always sparsely covered in fine hairs, and the upper stems may or may not have the same hairs.
  • Basal Rosette: In its early stages, bittercress often forms a basal rosette of leaves close to the ground.
  • Tall Seed Pods: As the plant matures, it produces distinctive elongated seed pods that can forcefully expel seeds when touched or disturbed.
  • Compound Leaves: The leaves of bittercress are compound, meaning they are divided into smaller leaflets along a central stem.
  • Opposite Leaf Arrangement: The round-to-oval leaves are arranged opposite each other along the stems, creating a distinctive pattern.

Life Cycle Of Hairy Bittercress

The life cycle of hairy bittercress is a testament to its adaptability and resilience. As a true winter annual, it germinates in the fall, establishing rosettes that persist through the colder months. With the arrival of spring, these plants grow rapidly and produce slender stems and their characteristic white flowers. The flowers give way to elongated seed pods that burst open, propelling seeds into the surrounding environment and starting the life cycle all over again. The breakdown below will provide a bit more information on each step in the life cycle of hairy bittercress.

  • Germination (Fall/Winter): Germination occurs when seeds are exposed to adequate moisture (fall or early winter), temperature, and light conditions, signaling the onset of favorable growing conditions.
  • Rosette Formation (Late Fall/Winter): Following germination, hairy bittercress seedlings develop into compact rosettes of leaves close to the ground. The rosette stage allows the plant to conserve energy and withstand adverse weather conditions during the winter months.
  • Flowering (Spring): As temperatures rise and daylight hours increase in the spring, hairy bittercress transitions from the rosette stage to the reproductive phase. This features rapid elongation of slender stems from the center of the rosette, eventually giving rise to flowers.
  • Seed Production (Spring/Early Summer): After pollination, the flowers give way to elongated seed pods known as siliques. These siliques contain numerous tiny seeds arranged in a single row within each pod, gradually maturing as the seeds develop.
  • Seed Dispersal (Late Spring/Summer): The explosive dispersal of hairy bittercress siliques enables seeds to be scattered over considerable distances. Factors such as wind, water, and human activity can aid in the dispersal of seeds, though they are not necessary for propagation.
  • Seed Dormancy (Late Summer/Fall): Despite the rapid dispersal of seeds, a portion of the hairy bittercress seed bank remains dormant in the soil, poised to germinate in subsequent growing seasons. Some seeds may germinate shortly after dispersal, while others may remain dormant for years.

How Does Hairy Bittercress Spread?

Explosive seed dispersal is the best way to describe the method through which hairy bittercress spreads. The process is facilitated by the tension buildup within its elongated seed pods. Upon reaching maturity, these pods rupture at the slightest touch or disturbance, launching seeds up to several feet away from the original plant. A single plant can produce between 600 and 1,000 seeds, with each silique containing about 30 seeds.

Though seed dispersal is the main way hairy bittercress spreads, this weed is also capable of regenerating from broken stems or uprooted fragments. Hairy bittercress has fibrous, shallow roots that can be difficult to remove by hand. Attempting to pull up one of these plants often results in tiny bits of roots being left in the soil to regenerate. 

Does Hairy Bittercress Damage Lawns & Gardens?

Despite its small size (no more than 12 inches tall), hairy bittercress poses a significant threat to the health and aesthetics of landscapes. Dense infestations can outcompete desirable vegetation for essential resources, such as nutrients, water, and sunlight, resulting in thin, patchy lawns or garden beds. As mentioned above, the unique and explosive seed dispersal means that a single plant emerging on your property can quickly turn into a widespread infestation. 

Hairy bittercress is also known to form dense mats in turfgrass as more and more plants begin to germinate and overtake the soil. For these reasons, timely and proper control of hairy bittercress is vital to the health of your lawn and landscape. 

Controlling Hairy Bittercress

As we have discussed, controlling hairy bittercress can be difficult for a number of reasons. This tenacious weed grows quickly, bursts seeds across your property, and can remain viable in the soil with even the tiniest bit of plant matter or seeds. The best approach is to cultivate a lush and healthy lawn that can choke out bittercress seedlings, but this is easier said than done. Herbicides can be used to both prevent and control hairy bittercress after all options have been explored. The tips below will help ensure that your property stays free of hairy bittercress this season.

  • Hand-Pulling: Employ hand-pulling for smaller infestations, ensuring thorough removal of the entire plant, including all of the fibrous roots. Prompt action before flowering prevents seed dispersal and curtails further spread.
  • Mulching: Apply a generous layer of organic mulch to garden beds and around trees and shrubs to suppress hairy bittercress growth. The mulch acts as a physical barrier, inhibiting seed germination while enhancing soil moisture retention and fertility.
  • Overseed In Spring & Fall: Creating a dense lawn is one of the best ways to prevent hairy bittercress. Spring and fall overseeding helps your lawn establish more turf and roots to discourage the weed seeds from germinating.
  • Fertilize With Nitrogen: Nitrogen helps grass grow lush while also improving resources in the soil to help lawn growth. Both of these factors will deter the growth of hairy bittercress by creating lusher lawns that crowd out the weeds. 
  • Apply Selective Herbicides: Utilize selective herbicides tailored for broadleaf weed control in lawns to manage severe hairy bittercress infestations. Adhere closely to label instructions, selecting products that target the weeds without harming your turfgrass.
  • Professional Services: Professional weed control specialists are the best defense against hairy bittercress and all other types of weeds. Lawn care companies can maintain a healthy landscape and safely apply any herbicides without you having to worry about a thing. Call a professional near you for more information on weed control services in your area.