Clay soil is a mixed blessing--or a mixed curse. Clay soil typically has lots of nutrients plants need to grow and thrive, such as calcium, potassium and magnesium. It also retains moisture well because of its dense nature. But most plants do poorly in clay soil because their roots aren't strong enough to penetrate it. There are, however, some notable exceptions, including several small flowering plants.
Chaenomeles, commonly known as ornamental or Japanese quince, is a low-growing shrub with clusters of bright red to pink flowers. Native to the forests of China and Japan, the quince flowers early and is very hardy. It withstands frost and is commonly used as ground cover.
Asters are hardy perennials that produce clusters of small, delicate flowers that look like tiny daisies. Common colors include white, purple, pink and red. The plants like full sun and form broad, bushy clumps. Asters are among the least-picky plants in a modern garden. They grow wild all over the world, in almost any environment, from dry deserts to swamps.
Pyracantha, known as firethorn, is a thorny evergreen shrub with clusters of small white flowers that bloom in late spring. After the flowers die off, they are replaced by yellow, orange or red berries. The shrub is hardy, and its leaves remain green year-round. Firethorn can be grown as ground cover or hedges.
One of the hardiest and longest-blooming,perennials commonly found in North American gardens, most species of coreopsis--and there are more than 80--have clusters of small yellow, pink or red flowers that stand upright on thin stems. Coreopsis rosea, with rose-colored flowers that resemble tiny daisies, is particularly suited to clay soil.
Mexican Orange Blossom
Choisya ternata, or Mexican orange blossom, is an evergreen shrub with glossy leaves and fragrant white flowers. Be sure to get the regular variety and not the yellow-leaf Sundance variety, which rarely flowers.