How to Spot and Treat Common Blue Flowered Weeds in Lawns

The Big Four: Identifying Blue Flowered Lawn Weeds

Blue flowered weeds in turfgrass are rarely just a cosmetic nuisance; they are aggressive competitors that exploit thinning lawns, compacted soil, and poor drainage. While their spring blooms might look picturesque, species like Ground Ivy and Speedwell form dense mats that choke out desirable cool- and warm-season grasses. Effective eradication requires precise botanical identification, as herbicide efficacy varies drastically between broadleaf species.

1. Creeping Charlie (Ground Ivy)

Botanical Name: Glechoma hederacea
Identification: Creeping Charlie features round to kidney-shaped leaves with scalloped (crenate) margins. The stems are square and root at the nodes (stolons). When crushed, the foliage emits a distinct minty odor. The flowers are small, tubular, and range from pale blue to violet.

Growth Habit: Perennial. It thrives in shaded, moist areas but will invade full sun if the turf is thin. According to the University of Minnesota Extension, its stoloniferous growth allows it to bypass standard pre-emergent herbicides, making post-emergent spot-treatment mandatory.

2. Henbit

Botanical Name: Lamium amplexicaule
Identification: Often confused with Creeping Charlie, Henbit is a winter annual. The key differentiator is the leaf attachment: upper leaves clasp the square stem directly without petioles (leaf stalks), whereas Creeping Charlie leaves have distinct petioles. Flowers are tubular and light purple to blue.

Growth Habit: Winter annual. It germinates in early fall, overwinters as a rosette, and blooms profusely in early spring before dying off in late May. The NC State Turffiles database notes that Henbit thrives in thin, poorly fertilized turf and compacted soils.

3. Speedwell (Veronica)

Botanical Name: Veronica filiformis (Slender Speedwell) or Veronica persica (Persian Speedwell)
Identification: Speedwell produces tiny, striking blue flowers with white lower petals, measuring only 1/4 to 1/2 inch across. Leaves are small, rounded, and deeply lobed. It forms a low-growing, dense mat that creeps just below the mower blade.

Growth Habit: Perennial or winter annual depending on the species. Speedwell is notoriously resistant to standard 2,4-D herbicides, requiring specialized active ingredients for control.

4. Wild Violets (Blue/Purple Variants)

Botanical Name: Viola papilionacea (syn. Viola sororia)
Identification: Heart-shaped leaves with finely toothed margins growing in a basal rosette. Flowers are five-petaled, typically deep blue-violet with a white throat, though color variants exist.

Growth Habit: Perennial. Wild violets possess a thick, waxy leaf cuticle and fleshy rhizomes that store carbohydrates, allowing them to survive both drought and standard broadleaf herbicide applications. Penn State Extension highlights that their waxy coating repels water-based herbicide sprays unless a surfactant is utilized.

Diagnostic Comparison Matrix

Spot-Treatment Protocols: Herbicide Selection & Application

Broadcast spraying entire lawns for isolated patches of blue flowered weeds wastes chemical and increases environmental runoff. Spot-treatment using a 1-gallon or 2-gallon pump sprayer is the most efficient and cost-effective methodology.

Protocol A: Eradicating Creeping Charlie & Wild Violets

Standard 3-way herbicides (2,4-D, MCPP, Dicamba) often fail against Ground Ivy and Violets. You must use a product containing Triclopyr.

• Recommended Product: T-Zone Turf Herbicide (approx. $45-$55 per quart) or Ortho WeedClear Lawn Weed Killer for Lawns (approx. $18 per 32oz ready-to-spray).
• Mix Rate (Concentrate): 1.5 fluid ounces of Triclopyr-based concentrate per 1 gallon of water to treat 1,000 square feet.
• The Surfactant Rule: For Wild Violets, you must add a non-ionic surfactant or methylated seed oil (MSO) at a rate of 0.25% v/v (approx. 1/2 teaspoon per gallon). This breaks the waxy leaf cuticle, allowing the Triclopyr to penetrate the plant tissue. Expect to pay $15-$20 for a pint of high-quality surfactant.
• Timing: Apply in early fall (September/October) when the weeds are actively pulling carbohydrates down into their roots for winter storage. This translocates the herbicide directly to the root system.

Protocol B: Eradicating Speedwell

Speedwell's biological makeup makes it highly tolerant to Triclopyr and 2,4-D. You need a product containing Carfentrazone-ethyl or Fluroxypyr.

• Recommended Product: SpeedZone Lawn Weed Killer (approx. $55-$65 per quart). This formulation combines Carfentrazone with 2,4-D, MCPP, and Dicamba, providing a 'burn-down' effect visible within 24 hours.
• Mix Rate: 2.3 fluid ounces per 1 gallon of water per 1,000 square feet.
• Timing: Apply in early spring when Speedwell is actively blooming and vegetative growth is rapid.

Protocol C: Managing Henbit (Winter Annual)

Because Henbit dies naturally in late spring, post-emergent treatment is only viable in early spring or late fall. If it is already May, let it die and focus on pre-emergents.

• Post-Emergent: Any standard 3-way broadleaf herbicide (e.g., Southern Ag Amine 2,4-D, approx. $25/quart) applied in March will kill it rapidly.
• Pre-Emergent (The Real Fix): Apply Prodiamine (e.g., Barricade) in early September when soil temperatures drop to 70°F to prevent Henbit seeds from germinating in the fall.

Organic and Non-Chemical Eradication Tactics

For homeowners managing organic lawns or dealing with weeds in garden bed borders where chemical drift is a concern, non-selective organic methods are viable, though they require more physical labor.

Horticultural Vinegar (20% Acetic Acid)

Standard 5% household vinegar is ineffective against established perennial weeds. You must use 20% to 30% horticultural acetic acid (e.g., Green Gobbler 20% Vinegar, approx. $25/gallon).

• Application: Spray directly onto the foliage on a hot, sunny day. The acid desiccates the leaf tissue within hours.
• Drawback: It is non-selective and will burn your desirable turfgrass. It also only kills the top growth; perennial roots (like Violets and Creeping Charlie) will likely resprout, requiring 3 to 4 repeated applications.

Manual Extraction Tools

For small infestations of Wild Violets, hand-pulling is ineffective because the fleshy rhizomes snap, leaving fragments that regenerate. Use a stand-up weeder with serrated claws (e.g., Fiskars Stand-Up Weeder, approx. $40). Push the claws 4 inches deep into moist soil, step on the foot platform, and lever the handle back to extract the entire taproot and rhizome network intact.

Post-Eradication Lawn Recovery

Spot-treating blue flowered weeds leaves bare patches in the turf canopy. If left unaddressed, these bare spots will be immediately recolonized by new weed seeds.

1. Rake the Area: Once the weeds have turned brown and died (usually 10-14 days post-spray), vigorously rake the dead organic matter to expose the bare soil.
2. Topdress and Seed: Apply a 1/4 inch layer of compost, followed by a high-quality, weed-free grass seed. For cool-season lawns, use a Turf-Type Tall Fescue blend (approx. $6-$8 per lb). For warm-season lawns, use Bermuda or Centipede seed.
3. Starter Fertilizer: Apply a starter fertilizer high in phosphorus (e.g., 18-24-12) to promote rapid root establishment of the new grass seed.
4. Hydration: Keep the top 1 inch of soil consistently moist for 14-21 days until germination is complete.

Frequently Asked Questions

Does pulling Creeping Charlie by hand work?

No. Creeping Charlie spreads via stolons (above-ground runners) that root at every node. Pulling it manually almost always leaves behind small stem fragments and nodes that will regenerate new plants within weeks. Chemical translocation via Triclopyr is the only reliable method for total eradication.

Why do my blue flowered weeds keep coming back every spring?

If the weeds return annually, you are likely dealing with a winter annual like Henbit, or you are spraying perennials (like Violets) at the wrong time. Spraying perennials in the summer only burns the top leaves. You must spray in early fall when the plant's biological drive is to pull nutrients (and the herbicide) down into the root system for winter dormancy.

Will borax kill Ground Ivy?

While older internet guides recommend mixing borax (sodium borate) with water to kill Ground Ivy, this practice is no longer recommended by turfgrass scientists. Boron does not break down in the soil; repeated applications lead to boron toxicity, which sterilizes the soil and prevents any desirable grass from growing in that spot for years.