Home gardeners often ask if wood ash can be used as a fertilizer in vegetable and flower beds, around landscape trees and shrubs, and on lawns. Ash can be a valuable source of certain nutrients and can also change the pH of the soil. However, it must come from an appropriate source, and its use should be based on soil fertility test recommendations. What is wood ash good for in the garden? Read on to learn important information that will help you strengthen your plants naturally.
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What are the benefits of using wood ash?
Wood ash contains nutrients that can be beneficial for plant growth. Calcium is the most abundant plant nutrient in wood ash and can make up 20% or more of the contents. Potassium (also called potash) is another common component of ash, occurring in concentrations up to 5%. Magnesium, phosphorus and sulfur are also commonly found in ash in concentrations up to 2%. Finally, wood ash may contain traces of iron, aluminum, manganese, zinc, boron, and other nutrients needed by plants.
In addition to its nutrient content, ash can help neutralize soil acidity. Burning wood produces large amounts of carbonates. Carbonates react with and neutralize the acid in the soil, raising the pH of the soil. The carbonate content of wood ash (and thus its acid-neutralizing properties) depends on the type of wood burned and how it is burned.
What are the possible disadvantages?
Occasionally, even the best wood ash may contain heavy metals such as cadmium and lead. However, the levels of these metals can be minimized by careful selection of the wood burned to produce the ash. In addition, the increase in soil pH associated with the use of wood ash reduces the likelihood that plants will take up heavy metals.
When ash is used in recommended amounts, heavy metal concentrations should be low enough that they do not pose a risk to plants, animals, or humans that eat crops grown on the treated land. Because the use of ash tends to increase soil pH, application in areas where acid-loving plants (e.g., blueberries, azaleas/rhododendrons, birch trees, red maples, live oaks) are growing is not likely to be beneficial. In fact, the use of wood ash can be harmful and contribute to chlorosis problems.
In addition, many vegetable and other landscape plants prefer slightly acidic soils, so wood ash should be used judiciously when growing these plants. Finally, elevated pH due to ash use can, in some cases, promote certain diseases. For example, potatoes grown at a higher pH are more susceptible to potato scab
What type of ash should I use?
If you choose to use wood ash for your gardening, you should only use ash from trees grown in natural areas. DO NOT use wood ash that comes from trees grown near industrial sites or in soils that may be contaminated with toxins or heavy metals, or if you do not know the source of the wood you are burning. Also, DO NOT use ash from burning treated wood.
What is wood ash good for in the garden: how to use it as fertilizer?
Sift the wood ash before application to remove large charcoal pieces and active embers. Apply only the amount of wood ash recommended based on a soil fertility test and the nutrient needs of the plants you plan to grow on the treated area. Application of excessive amounts may result in nutrient toxicity and/or nutrient deficiencies in the plants. Spread wood ash evenly over the area to be treated (e.g., vegetable bed, perennial flower bed, lawn, or other landscape area) during the winter.
Since the particles of ash are very fine and can be easily blown by the wind, do not apply when it is windy. Apply wood ash to moist soil whenever possible. Where possible (e.g., in a vegetable garden), work the ash into the soil in early spring with a tiller, spade, or rake. Wear appropriate protective clothing (e.g., long pants, long-sleeved shirt, gloves, safety glasses, dust mask) when working with ash to avoid exposure that could cause skin, eye, or respiratory irritation.
Plants that benefit from the application of wood ash.
What is wood ash good for in the garden? Ash is beneficial to many plants and shrubs, but some especially like it. These include:
- Cabbage plants such as cauliflower, broccoli and Brussels sprouts
Plants to avoid or limit the use of ash.
Ash is not a good choice for plants that like acidic soils and is not recommended for all plants. Generally, these are plants, trees and shrubs that prefer acidic soils and lower pH. Avoid using wood ash on: