It is, however, possible to plant straight into a wet heavy soil. Choosing the right plant for the right place is easily done, when a wet or damp loving plant is chosen. There are lots! The following are all plants that would cope with a soggier soil.
Rogersia aesculifolia has a mass of leaves at the bottom, like a horse chestnut leaf. They have spikes of pink flowers in summer.
Flag iris. There are many different flag irises, with typically blue or yellow, tall, striking flowers in later spring or early summer, variety depending.
Ferns. Many ferns are native to wet woodlands. They give foliage colour and texture to a shady border.