You can dig a bole 12 to 18 inches deep and fill it with water. If the water does not drain away easily in 5 to 10 hours, you will know that you cannot expect good results from plants requiring both air and moisture in the rooting zone. Their root zones must not become waterlogged. You can go to the expense of tile drainage or you can bring in new soil and use raised beds with stone borders to get a satisfactory rooting zone. Yet there are plants that tolerate wetness.
Many ferns do.
Some kinds like shade and others take sun. In moist shady places, you can use mosses. But unless you keep weed plants out, the moss cover will not be complete. It is more difficult to avoid dryness on slowly permeable sloping soils. When the rains fall heavily, most of the water runs off and, unless the soil is protected, the runoff takes some of the soil with it.