Picking right firewood can reduce ash

The weather in North Florida doesn't get as cold as it does further north, but every once in awhile there is a nip in the air and a toasty fire in the fireplace feels mighty nice. How do you choose the best wood for your fire place?

What can you do with all the resulting ash?

In Florida, we have a number of native and introduced species of trees to choose from. Pound for pound all wood burns about the same. A pound of good dry hardwood will produce about 8600 B.T.U.s of heat energy when burned.

Because of high resin content, some pine wood may produce over 9000 B.T.U.s. Hardwood and some tropical woods are denser than pine, and on a volume basis contain more heat value.

The denser (heavier) woods have the highest energy values so choose from the high-density group. Species with highdensity wood are: live oak, red oaks (including water and scrub oaks), white oaks, hickory, dogwood, Eucalyptus, and Australian pine (Casurina).

Species with mediumdensity wood are: beech, cherry, ash, sycamore, elm, Magnolia, gums, and red maple. Species with low-density wood: willow, cottonwood, and tulip poplar.

Most people have a personal preference when it comes to choosing firewood. Oaks, hickories and ash are usually preferred. Live oak is one of the heavier woods. It burns well, stores well and is widely available.

One problem is that it's difficult to split. Red oaks are plentiful and easy to split. They often have a sour odor when freshly cut. Ash has often been called the best firewood. Blackjack and other scrub oaks are preferred by some almost to the exclusion of other woods.

Dead, damaged and diseased trees along city streets are commonly felled by city crews but left for removal at the owner's expense. This wood is often available to the person who is willing to sacrifice an afternoon or weekend.

Utility companies trim trees along right-of-ways which sometimes produces a good supply of wood available to an alert public. Check with local utility companies on their policy for removing wood.

Once you have selected your wood, cut it, stacked it, burned it in your fireplace or wood stove, what do you do with the ash?

Numerous gardening books and news articles suggest incorporating these ashes in the garden or landscape soil.

Wood ash does have a nutrient value, but the amount depends on the species of wood. Generally, wood ash contains less than 10 percent potassium (K), 1 percent phosphate (P) and trace amounts of micronutrients such as iron, manganese, boron, copper and zinc.

Wood ash does not contain nitrogen (N). Wood ash contains about 25 percent calcium carbonate, a common liming material used to raise soil pH or soil alkalinity. Wood ash has a very fine particle size, so it reacts rapidly and completely in the soil.

Although small amounts of nutrients are applied with wood ash, the main effect is that of a liming agent. As soil alkalinity increases and the pH rises above 7.0, nutrients such as phosphorus, iron, boron, manganese, copper, zinc and potassium become tied up in the soil and less available for plant use.

It's difficult to make recommendations for the use of wood ash because soil varies from garden to garden. Before adding wood ash, do a pH test on your soil.

In general, acidic soils (pH less than 5.5) should improve by adding wood ash. Soils that are slightly acidic (pH 6.0 to 6.5) should not be harmed by the application of 20 pounds per 100 square feet annually.

Till the ash into the soil to a depth of about 6 inches. Do not add wood ash to soils that have a pH 7.0 or above.

Plant tolerance to alkaline soil also should be considered. Some plants, such as asparagus and juniper, are more tolerant of slightly alkaline conditions than "acid-loving" plants, such as potatoes, azaleas and blueberries.

Don't use wood ash on acid-loving plants.

- Source: Selecting Firewood, D. Mitchell Flinchum, Sept.,2006, District director, and professor in Forest Resources and Conservation

Dept., UF/IFAS. Wood Ash in the Garden, B. Rosie Lerner, Nov., 2000, Extension Consumer Horticulture Specialist, Purdue University.