One weed you’re almost sure to encounter sooner or later – especially in the U.S. Northeast and upper Midwest – is corn speedwell. This fast-growing, mat-former with the telltale blue flowers is both a rampant seeder and a plant that’s not terribly picky about where it grows.

Although it’s primarily known as an invader of lawns, corn speedwell also often shows up in landscaped beds, open untended fields, and even carpeting the ground of woodlands.

What Is Corn Speedwell?

Corn speedwell is a winter annual broadleaf weed native to Europe and parts of North Africa and Asia. It is common in the U.S. Northeast and upper Midwest but can grow in many regions.

It’s a plant that sprouts from seed primarily in late summer through fall, although some germination happens in very early spring.

The seedlings hug the ground with arms that quickly fan out to create dense mats of half-inch to three-quarters-inch oval leaves that have rounded, toothed edges.

The lowest level of foliage stays about two to four inches tall, but some stems (including the flower stalks) turn upright and can top out around a foot to 14 inches.

Plants grow fastest in the cool weather of early spring, producing the more erect stalks tipped with single blue to pale-blue flowers by late spring into early summer. That’s when corn speedwell is most noticed.

Plants die in the heat of summer after producing small yellow seeds that drop to the ground, setting the stage for a new cycle later that summer and fall.

Mats of blue-blooming corn speedwell are dominating this thin lawn in spring. Photo by George Weigel

Key identification features:

• Low-growing, mat-forming habit
• Oval leaves (½ to ¾ inch long) with rounded, toothed edges
• Stems that sprawl along the soil surface
• Small blue to pale-blue flowers in spring to early summer
• Shallow root system
• Grows 2–4 inches tall at the base; flower stems may reach 12–14 inches

Corn speedwell thrives in:

• Dry, sandy, or rocky soil
• Landscape beds and shady lawns
• Edges of shrub borders
• Open woodland areas
• Full sun or partial shade

It is less common in frequently disturbed soil, since young seedlings are easily uprooted.

How to Control Corn Speedwell in Lawns

Corn speedwell often appears in thin or weak turf, especially in early spring when its small blue flowers stand out against the grass. In lawns, control focuses on both removing existing plants and preventing new ones from germinating.

• Hand-pull small patches when soil is moist. The shallow roots make removal easy, especially before flowering.
• Spot-treat with a selective broadleaf herbicide labeled for lawn use. These products target weeds like speedwell without harming most turfgrasses. Apply during active growth in cool spring weather for best results.
• Always follow label directions carefully for safe and effective application.

How to Prevent Corn Speedwell from Returning

Long-term control focuses on eliminating conditions that favor germination.

In Flower and Shrub Beds:

• Maintain consistent 2–3 inch mulch coverage
• Avoid leaving bare soil exposed
• Remove plants before they produce seed
• Apply a pre-emergent weed control that targets crabgrass and other weeds in late summer

Because corn speedwell is a winter annual that germinates in late summer and fall, prevention is key, as is maintaining a thick, healthy lawn. Dense, vigorous grass naturally crowds out corn speedwell, limiting the light and space seedlings need to establish.

• Fertilize appropriately and mow at the correct height

• Overseed thin areas
• Reduce soil compaction and improve drainage where needed.

• Apply pre-emergent products in late summer before seeds begin germinating

Similar Weeds to Watch For

Corn speedwell is often confused with other Veronica species:

• Persian speedwell (Veronica persica): Larger flower stalks and leaves
• Ivyleaf speedwell (Veronica hederifolia): Three-lobed, ivy-like leaves
• American speedwell (Veronica peregrina): White flowers, also called purslane speedwell
• Field speedwell (Veronica agrestis): Larger leaves, later blooming blue and white flowers

Correct identification ensures proper treatment timing.

Quick Control Summary

Best time to prevent corn speedwell: Late summer (before fall germination)
Best time to remove existing plants: Early spring before flowering
Most effective bed prevention method: 2–3 inches of mulch
Why it returns each year: Seed production and fall germination

Final Thoughts

Corn speedwell may look delicate with its small blue flowers, but it spreads quickly in landscape beds and lawns if left unchecked. The combination of:

• Early removal
• Consistent mulching
• Proper herbicide timing
• Preventing seed production

…provides reliable, long-term control.

If you focus on prevention in late summer and eliminate seedlings early in spring, you can keep flower beds and shrub borders largely free of corn speedwell year after year.