Wild violet (Viola sororia) is a tenacious, perennial broadleaf weed recognized by its low-growing habit and glossy, heart-shaped leaves. This aggressive invader rapidly colonizes lawns, making it a formidable opponent for homeowners seeking uniform turf. Successfully removing wild violet requires understanding its unique biology and employing targeted removal strategies.
Why Wild Violet Is So Difficult to Control
Wild violet’s persistence stems from two distinct biological mechanisms. First, it has a robust underground structure consisting of a thick taproot and fleshy rhizomes, which are horizontal underground stems. These rhizomes store energy, allowing the plant to rapidly regrow even if the foliage is removed. Pulling the visible plant often leaves behind portions of the rhizome network, ensuring its return.
The second mechanism is the plant’s highly efficient reproduction, involving two types of flowers. While the familiar purple flowers are cross-pollinated, the plant also produces cleistogamous flowers that remain closed and hidden beneath the leaves. These unseen flowers self-pollinate, guaranteeing seed production. The resulting seeds are then forcibly ejected or dispersed by ants, leading to rapid colonization of new areas.
Manual and Cultural Removal Techniques
Non-chemical methods can address small patches or infestations in garden beds, though they require persistence. Hand-weeding is viable for limited infestations but must be intensive to be effective. The goal is to excavate the entire root system and all associated rhizomes, which is easiest after deep watering when the soil is loose. Since leaving even a small segment of the rhizome allows regeneration, use a garden fork or trowel to dig deeply around the plant’s base.
For larger, contained areas, smothering or solarization can kill the entire population and existing seeds. Smothering involves covering the area with a thick, opaque material, such as cardboard or heavy black plastic, for several months to block sunlight. Solarization, often more effective, uses clear plastic sheeting placed over moistened soil during the hottest part of the summer. This traps solar energy, creating a greenhouse effect that raises the soil temperature high enough to kill the plants and rhizomes over several weeks.
Horticultural vinegar, containing a high concentration (20% to 30%) of acetic acid, is a natural alternative for spot treatment. This concentration is non-selective and will burn any foliage it contacts, including turfgrass, requiring precise application. Because wild violet has a waxy cuticle, the vinegar must be mixed with a non-ionic surfactant, like a drop of dish soap, to help it adhere to the leaves. Since this method only kills the top growth, repeat applications are necessary to deplete the energy reserves stored in the roots.
Effective Chemical Treatment Options
Chemical eradication is often necessary for widespread infestations. The most effective products are selective broadleaf herbicides containing triclopyr. Triclopyr penetrates the wild violet’s waxy leaves and moves down to the root system. Many commercially available “3-way” herbicides also contain triclopyr along with 2,4-D and dicamba, broadening the range of weeds controlled in a single application.
The timing of the application is a major factor in the success of chemical control. The single most effective time to treat wild violet is in the late fall, typically from mid-September through early November. During this period, the perennial plant is actively moving sugars and nutrients from its leaves down to its roots in preparation for winter dormancy. Applying the herbicide at this time allows the chemical to be pulled along with the nutrients, delivering a lethal dose directly to the rhizomes and taproot.
Regardless of the chemical used, incorporating a surfactant into the spray solution is necessary. The waxy coating on the leaves causes water-based herbicides to bead up, preventing absorption. A surfactant, often called a spreader-sticker, breaks the water’s surface tension, allowing the herbicide to spread across the leaf and be absorbed. To maximize absorption, avoid mowing for two to three days before and three to four days after application. Also, ensure no rain is forecast for at least 24 hours following treatment.
Long-Term Lawn Health and Prevention
Once wild violet is controlled, long-term prevention focuses on cultural practices that favor dense, healthy turfgrass, which crowds out weeds. Raising the mowing height is a simple adjustment, as wild violet thrives in short, thin turf with ample light. Mowing at an appropriate height helps the grass blades shade the soil, reducing the light available for violet seeds to germinate.
Wild violets prefer moist, poorly drained soil, so improving the drainage in problem areas will make the environment less hospitable to the weed. Aerating the lawn can help break up compacted soil and allow water to percolate more efficiently. Overseeding the lawn with new grass seed in the fall is another practice that increases turf density. A thicker stand of grass competes successfully for water and nutrients, preventing the wild violet from taking hold and reestablishing its extensive root network.