A bog garden is a type of garden that employs permanently moist (but not waterlogged) soil to create a habitat for plants and creatures which thrive in such conditions. It may exploit existing poor drainage in the garden, or it may be artificially created using pond liners or other materials to trap water in the area. Any such structure must allow a small amount of seepage to prevent the water stagnating. For instance, a pond liner must be pierced a few times. Typically a bog garden consists of a shallow area adjoining a pond or other water feature, but care must be taken to prevent water draining from a higher to a lower level. The minimum sustainable depth is 40–45 cm (16–18 in). Good drainage is provided by gravel placed over the liner, and the bog can be kept watered by using a perfora