Can I use Wood Ash in my garden beds?
With winter in full swing, fireplaces burn daily. Wood ash is often thrown away without a second thought, and without you realising, you might be missing out on some good nutrients for your garden. The short answer to whether you should use wood ash as a fertiliser is “yes.” But, you must consider a few points.
Healthy soil is rich in carbon, and wood ash returns organic carbon to the soil. This means wood ash also plays a role in carbon sequestration—not a large one at the scale of a backyard garden, but every bit helps. 
Wood ash contains nutrients that can be beneficial for plant growth. According to the University off New Hampshire “Wood ash is a good source potassium (K) ~5%, calcium (Ca) ~25%, phosphorous (P) ~2%, and magnesium (Mg) ~1% which are essential plant nutrients. Crops have been shown to respond positively to K and P from wood ash. Other micro-nutrients in wood ash include boron, copper, molybdenum, sulfur, and zinc. Wood ash contains a significant amount of calcium, the primary substitute for lime to increase the pH of acidic soils. Wood ash is a natural substitute for lime to help maintain proper soil pH. Soil pH measures the soil’s relative acidity or alkalinity.”
It is crucial to know that not all plants benefit from wood ash. Wood ash neutralizes acid in the soil, increasing the soil pH, which will not please alkaline-loving plants. Wood ash has no nitrogen, so it is not a complete fertilizer. Adding compost to your soil will help meet your plants’ other nutrient needs.
Plants That Don’t Like Wood Ash
- Sweet corn, peppers, eggplant, rhubarb, parsley, sweet potatoes.
- Potatoes (Wood ash can lead to potato scab.)
- Blueberries, raspberries, and most other berries.
Wood ash can help with soil structure and porosity, allowing water to reach roots more easily. In the vegetable garden, vegetables and fruit such as tomatoes, eggplants, cucumbers, and beans particularly appreciate this nutrient boost. Vegetables such as cauliflower, broccoli, or artichokes also benefit from this natural fertilization.
Plants That Like Wood Ash
- Beans, strawberries, and stone fruit trees.
- Onions and garlic.
- Root vegetables like carrots, turnips, and beets.
- Greens like collards, lettuce, chard, spinach, and arugula.
- Brassicas like broccoli, cabbage, cauliflower, and Brussels sprouts.
- Lavender, basil, sage, catmint, and many other herbs.
Using Wood Ash
- Don’t allow wood ash to become wet before you apply it, or else many of the nutrients will leach out prematurely.
- If you are substituting wood ashes for garden lime, use twice as much wood ash as recommended for your soil.
- Generally, scatter about 50-70g per sqm. Do this on a still day and wear gloves to protect your hands.
- When sprinkled around plants, dry ashes irritate slugs and prevent them from “crossing the line” to chow down on those plants. However, ashes cease to be effective pest repellants once they become wet and do not affect slugs inside the line.
- You can continuously use wood ash in the compost pile. Sprinkle wood ash on top of the pile. Use one or two cups of wood ash each time 15cm of green or brown materials are added to the pile. Use no more than 5% of the total volume of compost. More is not better. Too much wood ash can slow or harm the composting process.
Store Wood Ash
The nutrients wood ash contains are soluble. Therefore, you must keep ash from the rain so it doesn’t wash out. Containers with close-fitting lids are perfect for keeping ash dry until you can use it.
With everything else you use in and around your home, be mindful before you dump ash in the bin. It is up to us to rethink all the waste we send to the refuse dump weekly. Read here on how we deal with kitchen scraps in the garden.
Stay warm and enjoy cuddling next to the fire or under blankets.
Tash and Family
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