Clay is one of the smallest of all natural soil particles, and it tends to pack tightly together with little air space. This lack of air space and high level of compaction make clay the heaviest and densest type of soil. Its density allows it to retain large amounts of water and nutrients, but this makes it difficult for air and moisture to penetrate the soil [source: City of Bremerton].
One of the keys to successfully gardening in clay soil is to work only under certain states and conditions. Dry clay is fairly smooth and soft, while wet clay is heavy and hard to work with. Try planting in autumn or spring when using clay, and avoid working on days when the soil is overly wet. To resist winter freezing, add compost or mulch to the top layer of clay each autumn, then leave the soil undisturbed until spring. The added organic material should make planting easier, and will also help to improve drainage and air flow.
The best plants for clay include richly colored flowers that require high levels of moisture. Try wisteria, rhododendrons and most flowering perennials [source: BBC].