What Is Spalted Wood?

Wood of all species is susceptible to fungal attack and eventually rotting away if the conditions are right (or wrong, depending on your perspective). If conditions are right, the fungal attack can cause distinct colorations or patterns to form in the wood. This process is called spalting.

Many woodworkers dream of finding the perfect piece of spalted wood, as it is hard to find wood in which the fungus has been working for just the right amount of time. If the fungus is left to work on the wood for too long before it is killed, the wood will become soft and useless from a woodworking perspective. If it is stopped too soon, the spalting may not be very vibrant or may be found only on a small area of the wood.

A basic definition of spalting is coloration found in wood that is caused by a fungus. Spalting in wood is often referred to in three distinct categories: pigmentation, white rot, and zone lines. A piece of wood that has been spalted may only have one type of coloration or it may have all three types.

Sometimes spalted wood will have hues of green or red that are caused by the fungus-producing pigments inside the wood. These pigmenting fungi will decay the wood, but they typically do so at a slower rate than other decaying fungi.

Often there will be lighter-colored wood inside the dark lines that cause the pattern in the spalted region of the wood. This is caused by white rot fungi. These fungi consume the lignin found in the cell walls and between the cells of the wood. The lignin has a slight pigmentation, so when it is consumed by the fungus, the area appears lighter in color.

One of the most noticeable characteristics of spalted wood is dark lines that are found wandering across the board. These are called zone lines. While there are specific fungi that cause pigments and white rot, there is not really a specific fungus that causes zone lines. Zone lines are a result of different fungi creating a wall to protect their area of the wood from other invading fungi. The zone lines and areas of white rot can be very distinct.

The conditions necessary for spalting to occur are the same as the requirements for fungal growth. If the fungi are not growing, the wood is not going to decay and discolor. The three things that fungi need to grow are water, oxygen, and correct temperature.

If the water content of the wood is too low, the fungi cannot survive. A moisture content above 20% is ideal. If the wood or log is placed underwater, fungi cannot survive because the oxygen supply is not sufficient to support growth. Most fungi prefer temperatures between 50 and 104°F, with the best growth occurring at temperatures between 68 and 90°F.

Common wood species that can be found spalted include sugar maple, birch, and sycamore, but spalting can also be found in many other species. Some folks try to spalt their own logs then saw them into lumber. While this process can work, it is unpredictable and time-consuming. But a quick search on the internet can result in finding some interesting strategies to try spalting your own wood. Spalted wood, if found before the fungi deteriorate the wood beyond use, can be a unique treasure for any woodworker.

To learn more about spalted wood and how landowners can generate income by selling it, check out this Extension Learn Now video on Hunting Spalted Wood Treasure. And join the presentation by Dr. Sanford Smith and Kevin Cook, Forester with the Penn State Forestlands Office, "Stalking Spalted Wood Treasure," on Friday, March 7 at the 2025 Forest Landowners Conference.