Vinegar is a dilute solution of acetic acid, a weak organic acid produced through the fermentation of ethanol. Yes, vinegar harms plants, but the extent of the damage depends entirely on its concentration and application method. When used improperly, the acid causes immediate, visible damage to plant tissue. However, at specific concentrations, it functions as a non-selective contact herbicide, limiting its effect to the areas it physically touches.
How Acetic Acid Damages Plant Cells
The harm caused by vinegar is a direct result of its low pH, or high acidity, which initiates rapid desiccation in the plant’s cells. Acetic acid disturbs the integrity of the plant’s cell membranes, which are composed of a lipid bilayer. The acid’s corrosive nature quickly breaks down these protective layers, effectively destroying the cell structure.
Once cell membranes are compromised, the plant tissue cannot retain moisture. This causes the water within the cells to rapidly leak out, a process known as desiccation. This desiccation is visible as immediate wilting and browning, or “burn,” on the plant’s surface, and is most pronounced on soft, above-ground growth like young leaves and stems.
Soil damage is possible if a high concentration of vinegar is poured directly into the ground. Excessively acidic conditions temporarily lower the soil’s pH, interfering with the plant’s ability to absorb essential nutrients like phosphorus and magnesium. This change is detrimental to plants sensitive to acidic soil, potentially leading to nutrient deficiencies and root stress.
Applying Vinegar as a Targeted Herbicide
The damaging properties of acetic acid are leveraged when using vinegar for natural weed control. Common household vinegar typically contains about 5% acetic acid. Horticultural vinegar is sold in much stronger concentrations, often ranging from 10% to 20%, and this higher concentration is far more effective at causing the rapid burn-down effect on weeds.
Vinegar acts as a non-selective, contact killer, damaging any plant material it touches. Due to this contact-only action, the acid typically only kills the above-ground foliage and stems. It does not move systemically through the plant’s vascular system, meaning it fails to kill the deeper root structure, especially in perennial weeds.
For the best results, vinegar should be applied on a warm, sunny day, which enhances the desiccation effect. Application should be avoided during windy conditions, which could cause overspray onto nearby cultivated plants, ensuring the vinegar only targets the intended weeds.
When using stronger horticultural concentrations, safety precautions are necessary. Wear gloves and eye protection, as the acid is corrosive to human skin and can cause irreversible eye damage.
Responding to Accidental Vinegar Exposure
If a desirable plant is accidentally sprayed with vinegar or exposed to a spill, immediate action is necessary to minimize cellular damage. The goal is to quickly dilute and flush the acetic acid from the plant tissue and surrounding soil. If leaves or stems have been sprayed, thoroughly rinse them with clean water immediately to wash away the acid before it breaks down cell membranes.
If a significant amount of vinegar spills onto the soil, the area must be heavily flushed. This involves pouring a large volume of plain water, ideally five times the volume of the spill, through the soil. For potted plants, flush the water until it drains freely from the bottom, which washes the acid away from the roots and prevents a lasting change in soil pH.
In extreme cases of a large spill on a container plant, repotting with fresh soil may be necessary if the pot lacks drainage holes or if acid exposure was high. For open ground, flush the area with water and then apply a small amount of an alkaline material, such as baking soda or lime, to chemically neutralize the remaining acid in the soil.