Apple cider vinegar (ACV) is a fermentation product made from crushed apples, used increasingly in the garden. Its utility stems from its primary active component, acetic acid. This acid chemically alters the environment it is introduced to. Understanding the concentration of acetic acid is the first step in using ACV safely and effectively for various gardening purposes.
Adjusting Soil and Water pH
The ability of apple cider vinegar to introduce acidity makes it a simple, temporary solution for plants that thrive in lower pH conditions, such as gardenias, rhododendrons, and blueberries. These “acid-loving” plants often struggle in alkaline soils because essential micronutrients like iron and manganese become chemically locked and unavailable for root uptake. By slightly reducing the pH of the soil or the water used for irrigation, ACV can temporarily restore the availability of these nutrients, helping to reverse symptoms like yellowing leaves.
To avoid damaging plant roots or beneficial soil microbes, a low concentration is necessary. Gardeners typically mix one to two tablespoons of standard 5% ACV into a gallon of water for use on container plants. For larger areas, some sources suggest a slightly higher ratio. This method should be viewed as a periodic adjustment rather than a permanent soil amendment, since the acetic acid quickly breaks down, and the soil’s natural buffering capacity will cause the pH to rise.
Using ACV as a Natural Herbicide
When applied in higher concentrations, the acetic acid in apple cider vinegar acts as a non-selective contact herbicide. The acid rapidly destroys the plant’s cell membranes, causing the leaves and stems to quickly desiccate. This action is most effective on young, newly sprouted weeds that have minimal root systems and tender foliage.
For weed control, ACV is typically used at full strength or in a one-to-one dilution with water. To improve the effectiveness of the spray, many gardeners add a small amount of liquid dish soap, which acts as a surfactant. The soap helps the acidic solution adhere to the waxy coating on the weed leaves, ensuring better absorption and coverage. However, because this solution is non-selective, care must be taken to ensure the spray only contacts the target weed and not the surrounding desirable plants.
Essential Dilution and Safety Guidelines
Successful use depends entirely on the concentration and application method of the ACV solution. Standard household apple cider vinegar contains about 5% acetic acid, which is suitable for both gentle soil adjustments and concentrated weed treatment. However, specialized horticultural vinegar can contain 10% to 20% acetic acid, and this higher concentration is highly corrosive and dangerous to handle, making household ACV the safer choice for general home use.
Test the diluted solution on a small, inconspicuous area of the plant or soil first to gauge the reaction. Never apply ACV solution during the hottest part of the day or in direct sunlight, as the combination of acid and heat increases the risk of leaf scorching. The leaves of most garden plants are highly sensitive to acetic acid and can be burned even by a mild dilution.
Gardeners should avoid using ACV on tender seedlings or newly transplanted young plants. When adjusting soil pH, the solution should be poured directly onto the soil, avoiding contact with the foliage. The risk of harm to beneficial soil microbes and fine root hairs increases with misuse.