Are Ashes Acidic?

Alkalizing Effect

• Wood ashes are not acidic but rather alkalizing. Composed of 25 percent calcium carbonate, wood ashes act as a liming agent, thereby, increasing the alkalinity and raising the pH when added to the soil. Neutral to alkaline soils are those that have a pH of 7.0 or higher. Anything below 7.0 is considered acidic.

  If your garden or landscape soil is overly acidic, wood ashes are useful for correcting and balancing the pH. Because the wood is already broken down to a fine ash, wood ashes decompose quickly, having an almost immediate effect on the soil pH. In addition to use in the garden landscape, when added to compost, wood ash reduces acidity and helps create a favorable alkaline environment for helpful microorganisms and bacteria that assist in the decomposition of compost materials.

Acidic Vs. Alkaline Soil

• A balanced pH helps to ensure healthy plant growth in the garden landscape. Some plants favor more acidic conditions, while others prefer an alkaline environment. So test your soil pH to ensure that your plants are provided optimal conditions.

  The pH of the soil affects the way plants absorb nutrients. In slightly acidic soils, nutrients are available and absorbed faster than neutral to alkaline soil. Depending on your plants' nutritional needs, this can be a good or a bad thing. If the soil is too acidic, plants receive an overdose of nutrients, which leads to toxicity. The result is stunted plants, reduced fruit production and, in extreme cases, death. Conversely, in soil that is too alkaline, the nutrients are bound to the soil, making them more difficult for plants to absorb. The result in this case is nutrient-deficient plants that lack vigor and are more readily attacked by pests and diseases.

Added Nutrients

• In addition to having an alkalizing effect on the soil, wood ashes also provide a small percentage of macronutrients, as well as trace amounts of micronutrients, which are essential for healthy plant growth. Wood ashes provide between 1 percent and 10 percent of potassium and phosphate. Adding wood ashes to the soil helps correct deficiencies in such nutrients, although the small percentage may require the use of other soil amendments in extreme cases.

  Wood ashes also contain trace amounts of essential micronutrients such as zinc, boron, copper, manganese and iron. Wood ashes do not contain nitrogen or sulfur, as these elements are burned away with fire. Hardwoods like oak or maple contain higher amounts of nutrients than softwood like pine or fir. Keep your ashes clean and dry prior to soil application, as nutrients are easily leached away from wood ashes with rainfall.

Application

• Before applying wood ashes to the soil, test your soil’s pH to ensure that you do not create an overly alkaline environment for your plants. Various acid-loving plants like rhododendrons, azaleas, blueberries and potatoes require a soil pH below 7.0 and do not respond well to wood ashes. On all other plants, start with a small amount and observe how your plants respond. Wood ashes should be applied no more than once per year at a rate of 20 pounds per 100 square feet. Work the ashes into the soil evenly at a depth of approximately 6 inches. Ashes left in large clumps or piles leach concentrated amounts of salts into the soil, which is bad for your garden plants.