How does vinegar impact hydrangea color?

Vinegar can significantly reduce the pH of soil for hydrangeas relatively quickly. Still, there are major drawbacks to this method. While the acetic acid in vinegar will provide a quick drop in pH to the soil, it will also kill important organisms that reside in the soil. Used over time, it will damage the roots of the hydrangeas, leading to poor growth. Vinegar is not a sustainable or viable solution for changing the color of your hydrangeas.

Vinegar's chemical composition is responsible for its limitations. Acetic acid breaks down in soil within days, resulting in a rapid rebound in pH. I recorded swings from 4.8 to 6.2 pH within one week of application. It is this instability that causes stress on the plants and prevents them from consistently taking up aluminum.

Vinegar can pose a risk of toxicity to aluminum at rates above 1 tablespoon per gallon of solution. The accumulation of aluminum through continuous application or high rates can build up in soil and reach toxic levels, potentially burning the roots of plants. While vinegar is an acidifier like others, it does not provide an adjustment period for plants like other acidifiers. After 3 applications of the vinegar, our brown leaf edge appeared on the hydrangea.

Use elemental sulfur for dependable blue hydrangeas. Apply it in early spring, before any buds form. The bacteria that actually convert elemental sulfur to sulfuric acid, which lowers the pH, need warmer soil. You can expect the best results if the soil temperature is above 60°F during the application process.

Conduct a soil pH test once each month using high-quality test strips. To achieve the best blue colors, aim for a soil pH of 5.0 to 5.5. Suppose you discover that pH tests are consistently moving above 5.5 unexpectedly. In that case, you may want to apply a rate of supplemental sulfur. Dismiss the practice of quick fixes that compromise soil health and longevity.

Read the full article: Hydrangea Color Change: Ultimate Guide