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Burning Questions

Using wood and wood ash

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With the cool weather come thoughts of a crackling fire, an overstuffed chair and a good book. My mailbag is smoking with questions on wood use and wood ash; let's burn through a few of them.

Ann H. of Meridian asks: My neighbor and I have a running debate going over which wood is better for heating. I like pine, but she buys apple wood. Which is better?

Your neighbor wins. Apple wood is rated as a high heat source while most pines, with the exception of yellow pine, are rated only medium to low. Hardwoods, because they have greater density than softwoods, will have more BTUs per equal unit of volume. (BTU is the quantity of heat required to raise the temperature of one pound of water by one degree Fahrenheit.) That means a cord of seasoned oak, for example, contains approximately 60 percent more BTUs than a cord of seasoned pine.

The following woods are rated as the highest source of heat: apple, ash, beech, dogwood, black locust, madrone, sugar maple, red oak, white oak and mesquite. Those rated as high to medium heat sources are: box elder, yellow birch, red maple, yellow pine, tamarack and walnut. Not all these woods are available in Idaho, but at least the next time you get into a heated discussion over wood as an energy source, you'll know the answer.

For more information on wood selection, contact the Forest Service, your local University of Idaho Extension office or the Bureau of Energy Resources in Boise for brochures on heating with wood and woodstove safety.

Bill M. of Boise wonders: How do I know if I'm getting a full cord of wood? The man who delivers my wood just dumps it out of his pickup onto my driveway.

The only way to figure that one is to restack the wood so you can measure it. A standard cord of wood measures 4 feet by 4 feet by 8 feet. That's a volume of 128 cubic feet.

To calculate the number of cords in a big stack of wood, multiply the pile's height by its length and then by log length (all in feet). Divide what you come up with by 128.

Debbie C. of Kuna asks: Is it helpful or harmful to spread wood ash in the garden?

Wood ash from woodstoves and fireplaces can be plentiful, but its benefit will depend on the pH of your soil. Here's your chemistry lesson for the day:

A pH reading tells the acidity or alkalinity of your soil. You might think, Who cares? But the chemistry of the soil is very important because it determines what nutrients or minerals will be available to your plants. On the pH scale, anything above 7.0 is alkaline and anything below 7.0 is acidic (the scale runs from zero to 14).

Most people pay more attention to the pH balance of their shampoo than they do to the pH of their garden soil. However, good gardeners know that an ideal soil pH for most plants is slightly acidic--6.3 to 6.8--and they strive to attain such a pH by adding humus and other amendments to coax their soil into that range.

Soils in and around Boise tend to be alkaline, with pH readings somewhere between 7.1 and 7.9. An exception would be soils near the river or in the foothills where there is a lot of sand or gravel. Those soils can often be acidic as are soils in the mountains, like the areas around McCall and Cascade.

Wood ash tends to be alkaline in nature; consequently, adding ash to an already alkaline soil will just make the soil more alkaline--an undesirable condition for the growth of many plants. Soils that are too alkaline will make nutrients like iron, zinc, boron, copper and manganese unavailable and the plants grown there will start showing nutrient deficiency symptoms.

Lucky gardeners with acidic soils can use wood ash because the alkalinity of it won't hurt their gardens, plus it will add valuable nutrients. Wood ash is also high in potassium, calcium and magnesium.

If you don't know what your pH is, give yourself an early Christmas present and have a soil test run on your yard or garden soil. The test will give you some valuable baseline data that can help you determine your soil's characteristics and possible deficiencies. Your plants will thank you.

A standard soil test through a laboratory will cost around $30 to $40, depending on the laboratory and the types of tests requested. Avoid purchasing those cheap home test kits; they aren't accurate enough. Check the phonebook for a soils lab near you or contact a University of Idaho Extension office. They also conduct soil tests.

Suzann Bell is a horticulturist with the University of Idaho Extension in Ada County. Send gardening questions to Suzann c/o Boise Weekly or e-mail sbell@uidaho.edu.

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