Clay soil is the heaviest and most nutrient-rich of all the soil types. Its downfall is its poor drainage capabilities, which can limit the types of plants that will thrive in this soil. Ground cover plants that do well in moist soils are typically a good choice. When choosing ground cover plants beware of varieties that claim they will grow rapidly in any soil type or sun exposure. These ground covers are usually quite aggressive and can quickly take over a growing area, and adjacent areas, if not kept in check.
The marsh fern is a perennial fern with leaves that can reach heights of 1 to 2 1/2 feet. They are capable of adapting to a wide variety of soil conditions and growing environments. They can be found in damp, sandy meadows to marshes and bogs. They will grow in clay soils, so long as they are provided with exposure to sun, with full sun being preferable. The marsh fern dies off completely in the winter, but makes a full recovery come spring.
Snow-on-the-mountain is an annual plant with small, showy leaves that can range from all white to light green in color. Its tiny, white flowers sit, in clusters, on top of the plant's stem. This ground cover is native to the United States and can reach a height of 1 to 3 feet. It prefers partial shade and moist soil conditions. Be advised that snow-on-the-mountain is considered poisonous to humans and animals, so keep an eye on children or pets around this ground cover. The upside is that wildlife will not forage off this plant.
This large, leafy plant makes an attractive ground cover with its wide range of leaf colors. The leaves can be a solid color, in shades of blue or green, or variegated. Hostas produce a long stem from the center of the plant, with a cluster of small flowers growing from the tip of the stem. The plant ranges in height from 0.5 to 3 feet, with the individual leaves ranging 2 inches to 1 foot in length. Depending on the variety chosen, the flowering stem can reach 0.5 to 6 feet in height, but these only last approximately two weeks. They thrive in partial shade, preferring full exposure to the morning sun and shade in the heat of the afternoon. Hostas do well with the acidity and nutrient-rich environment of clay soils, but it is recommended to add peat moss to the soil and work it in to improve drainage.