So now we come to the part most people want to know -"How do keep my fence posts from rotting without spending any money"? The simple & best answer is - use the right wood. All trees have different characteristics & one of those is "resistance to decay". Simply put, some woods are more appealing to fungi & bacteria than others. This resistance is caused (generally) by chemical compounds, created by the tree itself. These compounds are called "extractives" and come in different forms. They are contained predominantly in the heartwood of the tree. Many of us have seen a log in the forest covered in rotten, pulpy and soaking wet decay and yet the heartwood is still whole & solid. Those extractives have protected the wood even while the sapwood was completely consumed. These natural compounds are as durable as anything man made, are already in the wood & free. The easiest way to determine if a tree will make a good post is to search "decay resistance of ------" anything described as poor or moderate or non-durable should not be used. Be as specific as possible because there is a wide variation among species, for example if you Google "decay resistance oak" you need to know what species of oak. Red oak decay resistance is poor / non durable while White oak is very good / durable. Obviously this depends on the trees available in your area, but that's the idea. A misconception about decay resistance is that "hard" woods are more resistant that "soft" , this is not correct, it depends entirely on those extractive chemicals not the relative hardness of the wood. As far as treating wood that is not naturally decay resistant, there are some low cost options. My favorite is placing posts in a barrel and dumping wood ash from the stove in and soaking with water. This saturates the wood with lye and discourages the decay causing organisms. Lye is water soluble so it will eventually leach out and leave the wood vulnerable. An old belief that charring the wood prevents decay is not really effective, charcoal is virtually decay proof but the wood beneath is not. At best charring may add a couple of years durability. So to conclude, remember that moisture must be present to cause decay but does not itself cause decay. Keeping wood dry is the best way to preserve it. Chemical treatments that discourage fungi & bacteria are effective but must be understood for safe use. Naturally decay resistant woods are an excellent resource if you can identify them. I hope this helps, if you have questions or comments I'll be happy to respond.
And by the way, termites cannot digest wood. Microbes/ bacteria in their digestive tracts convert the macerated wood into simple sugars and that nourishes the termite. It's all about those fungi, microbes and what not
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