11 Weeds with Blue Flowers: Identification and Control

Weeds are unwelcome intruders that disrupt the beauty and balance of our green spaces. But weeds with blue flowers can be alluring and can easily be mistaken for other garden flowers. So, is the blue flower in your garden a weed?

Read on as we delve into the world of blue weeds, detailing their characteristics and discovering effective methods for managing their growth.

Blue-Eyed Grass (Sisyrinchium angustifolium)

Blue-Eyed Grass is not an actual grass but a perennial weed with striking blue flowers resembling miniature irises. The flowers have six petals arranged in a star-like shape and a yellow center.

This charming plant thrives in meadows and open spaces but can compete with desirable plants for resources if left uncontrolled.

The most appropriate way to control Blue-Eyed Grass is through manual removal. This involves carefully pulling out the weed, including its roots, to prevent regrowth. Remove the entire plant, as Blue-Eyed Grass can reproduce through seeds.

Asiatic Dayflower (Commelina communis)

The flowers of the Asiatic Dayflower are small and blue. These flowers have three petals, with two larger petals on top and a smaller petal at the bottom. The blooms usually last only one day, giving the plant its name.

This herbaceous annual plant has sprawling stems that often root at the joints and can grow up to 1-3 feet tall. The leaves are alternate, oval to lance-shaped, and the stems are smooth and hairless.

Asiatic Dayflower is a potentially invasive weed, particularly in the southern and eastern regions of the United States, although its presence in the Upper Midwest is growing. It prefers moist soil and can be found in part shade or shade habitats.

Regularly hand-pull or dig out Asiatic Dayflowers, including their roots, especially when young and before they can produce seeds. This method helps prevent regrowth and reduces the spread of the weed.

Apply a layer of organic mulch around desirable plants. This suppresses the growth of the Asiatic Dayflower by smothering it and reducing its access to sunlight.

Green Alkanet (Pentaglottis sempervirens)

Green Alkanet produces vibrant blue flowers that resemble forget-me-nots. The flowers have five petals and a yellow center, creating an eye-catching display.

This herbaceous perennial plant can grow up to 3 feet tall. The leaves are large, rough, and hairy, while the flowers are bright blue and star-shaped.

Green Alkanet spreads through self-seeding and can form dense stands if not controlled. Its invasive nature and ability to outcompete native plants make it a concern in some areas.

Glyphosate-based herbicides can effectively kill Green Alkanet, along with other unwanted vegetation. Glyphosate products are available in various formulations, including ready-to-use sprays or concentrates that must be diluted before application.

2,4-D is effective against Green Alkanet but may also harm desirable broadleaf plants. Use it with caution and follow the instructions on the product label carefully.

Dicamba is another selective herbicide that controls Green Alkanet in lawns and other non-crop areas. Like 2,4-D, dicamba should be used carefully to avoid damage to desirable plants.

Forget-me-not (Myosotis scorpioides)

Forget-me-not is among the weeds with blue flowers. Often found in damp areas or along water bodies, Forget-me-nots are delicate flowers with enchanting blue petals (five petals) and yellow centers. Some cultivars have shades of pink and white.

Broad-spectrum herbicides that contain active ingredients such as 2,4-D, dicamba, triclopyr, or glyphosate can be effective against Forget-me-not.

Chicory (Cichorium intybus)

Chicory (Cichorium intybus) is a weed with composite flowers that form clusters at the top of its stems. The vibrant blue ray flowers, sometimes pink or white, have elongated petals with rounded lobes. Blooming in summer, they open in the morning and close by midday.

This weed often grows along roadsides and in open fields. It has a long taproot and can be challenging to eradicate.

You can manually remove chicory for small infestations by pulling it out from the base and removing the entire root to prevent regrowth.

Regularly mowing or cutting down chicory plants before they flower can help reduce seed production and limit their spread.

Viper’s Bugloss (Echium vulgare)

Viper’s Bugloss (blueweed or blue devil) is a biennial or short-lived perennial weed. It features dense spikes of vibrant, tubular flowers, typically deep blue or purple.

The flowers open gradually along the spike, creating an eye-catching display. However, despite its attractive appearance, Viper’s Bugloss is a weed due to its invasive tendencies and ability to outcompete native plants.

Viper’s Bugloss grows to a height of 1 to 3 feet (30 to 90 cm). It has an upright growth habit with multiple stems arising from a basal rosette of leaves. The leaves are lance-shaped and hairy, with a rough texture. They grow in a basal rosette during the first year.

Blueweed (Echium plantagineum)

Also known as Paterson’s Curse, Blueweed is an invasive weed with blue flowers found in pastures and open grasslands.

The flowers are arranged in dense spikes, with numerous individual flowers closely packed together. Each flower has a tubular shape with five petals fused at the base, forming a distinct trumpet-like structure.

It is native to Europe but has become invasive in some regions, including parts of North America and Australia. The plant has hairy leaves and stems. It competes with native plants and can cause harm to livestock if ingested.

Blueweed Speedwell (Veronica polita)

Blueweed Speedwell is a herbaceous flowering plant that belongs to the plantain family (Plantaginaceae). It’s one of the weeds with blue flowers that makes our list.

Blueweed Speedwell produces small, delicate, bluish-purple or violet flowers. The flowers are arranged in dense clusters along the upper portion of the plant’s stems.

Each flower has a distinctive shape, consisting of a tubular or funnel-like corolla with four fused petals.

The petals are usually a shade of blue, with darker veins running through them. The flowers have a white throat and a prominent yellow or white center, where the flower’s reproductive structures are located. The blooms are about 1/4 to 1/2 inch in diameter.

Blueweed Speedwell typically grows 8 to 20 inches (20 to 50 cm). It has an upright and bushy growth habit, with multiple stems emerging from a basal rosette of leaves.

It can be found in various habitats, including meadows, open woodlands, roadsides, and disturbed areas. It prefers well-drained soils and can tolerate both full sun and partial shade.

Blue Flax (Linum perenne)

The flowers of Blue Flax (Linum perenne) are typically small and delicate with a lovely shade of blue. Here’s a description of their appearance:

The flowers are cup-shaped and have five petals arranged in a radial pattern. Each petal is usually around 1 inch (2.5 centimeters) long and narrow. The petals are a vibrant sky-blue color, sometimes ranging from pale blue to purple-blue.

Blue Flax flowers have a bright yellow center with numerous stamens surrounding a central pistil. The stamens are the male reproductive parts that bear the pollen, while the pistil is the female reproductive organ that receives the pollen for fertilization.

The blooms often open in the morning and close in the afternoon, following the natural rhythm of many flax species.

Blue flax grows up to 2 feet tall, with slender, wiry stems and narrow, lance-shaped leaves. They prefer well-drained soil and full sun, often thriving in dry, sandy, or rocky areas.

Maintaining a healthy, dense turf or ground cover can help prevent the establishment of blue flax. Regular mowing and removing plant debris can also reduce its growth.

Spiderwort (Tradescantia spp.)

Spiderwort flowers are typically small to medium-sized, measuring around 1 to 2 inches (2.5 to 5 centimeters) in diameter. They have three petals, which are often vibrant and eye-catching, ranging in color from shades of purple, blue, pink, and occasionally white. The petals are delicate and usually have a slightly translucent quality.

At the center of the flower, you’ll find a cluster of yellow stamens, which are the male reproductive parts. The slender stamens extend outwards from the center, adding to the unique appearance of the flower. They often have yellow pollen at their tips.

They are often found in gardens, meadows, and woodland edges and can be invasive. You may consider using herbicides if manual removal is not feasible or the infestation is severe. Look for a herbicide specifically targeting broadleaf weeds and follow the instructions on the label carefully.

Glyphosate-based herbicides can be effective, but they are non-selective and will kill any plant they come in contact with, so be cautious when applying near desired plants.

Houndstongue (Cynoglossum officinale)

Houndstongue is a biennial or short-lived perennial plant native to Europe and Asia but has become invasive in many parts of North America. It can grow up to 1 meter (3 feet) tall and has distinctive clusters of flowers. It’s a weed with tiny blue flowers. 

The flowers of houndstongue are small and bell-shaped, typically measuring around 1 centimeter (0.4 inches) in diameter. They are arranged in dense, rounded clusters at the tips of the branches. 

The flowers are reddish-purple, often with a white or pinkish center. The petals are fused at the base, forming a tube-like structure.

Eradicating Houndstongue (Cynoglossum officinale) can be challenging due to its ability to produce abundant seeds and establish a persistent root system. 

Selective herbicides can be used for larger infestations. Herbicides are typically most effective when applied during the plant’s active growth stage.

Get Rid of Blue Flowered Weeds

While weeds with blue flowers may possess an undeniable allure, they can disrupt the growth of desirable plants and compromise the overall health of our landscapes. 

Learning to recognize and effectively manage blue weeds helps us preserve the beauty of our gardens while fostering an environment that promotes the growth of desired flora.