All wood should be seasoned before burning for the appropriate amount of time. Different woods have different initial water content, often determined by where a tree grows. Willow, for example, likes to grow in wet soils or besides water bodies, therefore the wood from this tree has a high water content and requires longer seasoning. Firewood should have a moisture content of below 20% at least for burning. The density of the wood also affects how long it needs to be seasoned for. Oak is a very dense wood and can take up to 2 years to season fully.