I have some trees to remove in my garden over the next few years that include invasive buckthorn. I was wondering if I can use the wood for an indoor fireplace?
— Joel Zimmerman, Waukegan
The most important thing is to make sure that the wood 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 the 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 it can be burned 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 can also 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 are 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 not be good to burn. Stack the 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 rain, but 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.
I have had good success using logs from a variety of different trees such as ash, oak, crabapple, buckthorn, birch and maple from pruning or removals for burning in my fireplace. Though it is possible to burn properly seasoned pine in a fireplace, I avoid doing so. Pine wood contains a lot of resinous sap, so it produces a lot of creosote, especially if it has not been 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 out into the room.
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For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at [email protected]. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.