Properly seasoned wood is essential for fireplace safety

I have some trees to remove in my garden next year and was wondering if I can use the wood in an indoor fireplace. My ash tree appears to be infested with emerald ash borer (I stopped treating it a few years ago). I also have some large, invasive buckthorn to remove. Is it OK to use the wood from these trees as well as other kinds of trees in my garden?

— Pam Novak, Lincolnwood

Consider removing the ash tree in your garden first, as it can quickly become a hazard after it dies. You can use ash wood in your fireplace. It is a good idea to plant a variety of replacement trees that are appropriate for your growing conditions. Trees that are well adapted to their growing conditions will establish more quickly, require less maintenance and be healthier overall and more resistant to disease and insect problems. Wood from buckthorn can also be used in your fireplace. Bulk firewood is sold by the cord, or a portion of that, such as a half or quarter cord. A cord of wood measures 8 feet long, 4 feet high and 4 feet deep.

The most important thing to consider for burning your wood is that it is properly seasoned before burning it in the fireplace to minimize the buildup of creosote in the chimney. Creosote is a highly combustible substance that condenses in liquid form as wood exhaust cools in the chimney and then solidifies as it dries. It is a product of combustion and builds up when fireplace operation is cool and inefficient with smoky, smoldering wood that is unseasoned or wet. Properly seasoned wood produces the most heat and the least amount of creosote. Freshly cut wood contains up to 80% moisture and needs to be seasoned (dried to 20-25% moisture content) before burning it indoors. Wood containing more than 25% moisture is considered green and should never be burned in a fireplace or wood stove in a building. Be sure to have your chimney cleaned regularly when using a fireplace or wood stove. A trained, professional chimney sweep will clean your chimney with the proper equipment and inspect it for cracks, water leaks, misalignment and deterioration.

Season the wood you generate with the removals by cutting up the logs and splitting them into fireplace-sized pieces that ideally will be stacked out of the rain for at least nine months. Hardwoods like oak will burn better if seasoned for more than a year. Improperly seasoned hardwoods can also smolder and lead to the buildup of creosote. The best wood is typically seasoned for one to two years but will start to deteriorate after four to five years and is not good to burn. Stack wood off the ground and in a way that allows air to circulate and carry away the moisture as it evaporates through both ends of each piece. Protect the woodpile from the rain, but try to avoid completely covering it with plastic tarps as air circulation is necessary for proper seasoning. If steam bubbles and hisses out of the end grain as the firewood heats up on the fire, the wood is wet or green, and needs to be seasoned longer before burning. Other signs of unseasoned wood are bark that is tightly attached and a wet, fresh-looking center with lighter and drier-looking wood near the edges or ends. Seasoned wood has a dark or gray appearance when compared to green wood. When you split a seasoned piece of wood, it will have more of a white color on the inside with cracks running through each piece and a lot of small cracks on the inner rings. The wood will also be more brittle. The wood from dead trees will be ready to burn much sooner than wood from a live tree.

I have had success using logs from a variety of different trees including ash, oak, crab apple, buckthorn, birch and maple from pruning or removals for burning in my fireplace. Be careful when splitting your wood with an ax, as it is easy to slip with the ax and injure yourself. I make sure my two small dogs are in the house when I split wood, as pieces often go flying from the log as the ax cuts through. If you have a lot of wood to split, consider renting a gas-powered log splitter. I avoid burning pine wood, which contains a lot of resinous sap and produces a lot of creosote, especially if it is not seasoned properly. I also avoid wood from juniper and arborvitae as they tend to pop and spark as they burn, which makes me nervous about having embers blow into the living room.

For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at plantinfo@chicagobotanic.org. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.