I have a low point in my backyard and the newly planted plants are not doing well. What should I do?
Instead of fighting with the planting site or quality of soil why not look at it as an opportunity to grow plants that don’t reach their full potential in drier, well drained conditions.
Garden Making magazine has an excellent article 16 plants for boggy soil listing plants for soggy shade as well as soggy sun locations.
The RHS-Royal Horticultural Society has an excellent article on Bog Gardens
The Toronto Master Gardener post, Flowering perennials for wet boggy areasalso gives a list of perennials suitable for this type of environment.
The key to success is to plant the right plant in the right place.