When assessing your garden site, you will need to check the water table - the level of water found naturally in the ground at different times of year. This can be checked easily by digging trial holes in different parts of the garden.

Most roots grow in the top 45 cm (18 in) of soil, and so if the water table stands higher than this, you may have to consider solving the problem by draining the ground, or alternatively, work around the problem by growing water-loving plants.