We just took delivery of a truckload of Black Locust fence posts. As you can see, they are not the straightest. Steve likes them crooked, because it hides the fact that he cannot drive a post in straight anyway. But the main reason we like them is that Black Locust lasts longer than any other kind of wood available. That even includes pressure-treated wood (which we are not allowed to use under the Organic rules).
The Black Locust tree has a long list of virtues. It is a legume, which means it gets its nitrogen from the air, so it can grow in poor soils without fertilizer. It grows incredibly fast, making it a renewable and “sustainable” resource. As firewood, it has the highest heat content of any wood common to the United States (comparable, in fact, to anthracite coal). Black Locust blossoms produce such delicious honey that the trees are widely planted in Europe for honey (however, it blooms only 10 days per year, making the honey rare as well as delicious). And Black Locust lumber is prized for everything from shipbuilding and furniture making to flooring and siding.
Sadly, Black Locust trees are susceptible to damage from a beetle called a Locust Borer. Infestation is so widespread, that it is difficult to find wood that is not affected. Borer infestation causes deformed growth and generally makes wood useless for lumber—hence the crooked fence posts.