Thrifty gardeners with fireplaces or wood stoves in their homes are fortunate. Not only can they save on energy costs by using the fireplace to heat their homes, but they also have a source for free, nutritious additions to their garden soil -- wood ash. Wood ashes not only benefit vegetable gardens, but also flower gardens and lawns. Each cord of wood you burn in the fireplace or wood stove yields roughly 9.07kg. of ashes.
Benefits of Wood Ashes
Wood ash not only provides nutrients to the soil, but also slightly alters the soil's acidity, or pH level. Fireplace ashes contain phosphorous, magnesium, potassium and calcium carbonate, or lime. Calcium carbonate makes the soil more alkaline, or "sweet." The exact percentages of phosphorus, potassium, magnesium and calcium vary according to what type of wood burnt. Wood ash contains no nitrogen. Ashes generally contain about three times as much calcium as potassium. Phosphorous content is usually about 1 to 3 per cent. Add ash when soil test results show your soil's pH is too low or deficient in potassium. If you forgo the soil test, limit the amount of ash you add to your garden soil annually. Use no more 0.454kg. of ash per year on shrubs and roses, and 4.54 to 6.8kg. per 1,000 square feet of lawn, vegetable garden or flower garden.
The ash left behind when you burn hardwoods such as oak has more nutrients than ashes from soft wood sources. As a fertiliser, hardwood ash provides more nutrients per pound than softwoods, so a little goes a long way in terms of both feeding your plants and the amount of work you have to do to incorporate the ash into the soil. When preparing a garden bed, mix the ash into the soil thoroughly. Spread ash on lawns and water it into the ground. Spread around perennials and other established plants, then gently rake the ash into the soil around the plants.
Ashes from softwoods like fir or pine contain about 1/5 as much phosphorus, calcium carbonate and magnesium as the ashes from hardwoods. You can add more softwood ash to your garden soil to make up the difference, but mix the ash with the soil thoroughly if you are getting ready to plant. Softwood ashes have about half the potassium of hardwood ashes.
If you use your fireplace to burn cardboard, painted or stained wood and other trash, do not collect the ash for the garden. These materials leave toxic residue in the ash that may pollute the soil and harm your plants. Because ash lowers pH in the soil, do not use it on acid-loving plants like blueberries, azaleas or rhododendrons. However, feeding fireplace ashes to a hydrangea plant can help alter the colour of the flowers.
Ashes may have some insect-repellent ability. Ashes can also help to maintain neutral acidity in compost bins, which helps the material break down more quickly.
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- National Gardening Association; Recycling Fireplace Ash; Charlie Nardozzi
- Fine Gardening; Using Ashes in the Garden; John Fech
- Alabama Cooperative Extension; Test Soil Before Using Fireplace Ashes in the Garden; Dave Williams, PhD.; Jan. 5, 2001
- Oregon State University Extension; Wood Ash Can Be Useful in Yard if Used With Caution; Carol Savonen
- Iowa State University; Wood Ashes on the Garden; Linda Naeve; Feb. 23, 2005