Black gum & bald cypress trees
Two trees come immediately to mind that thrive under wet or heavily compacted conditions. The first is our native black gum, Nyssa sylvatica. This tall tree is relatively slow-growing but will obtain a height of 50 feet or more. As with many species tolerant of wet soils, growth will be accelerated if the soil is moist and dramatically reduced if the soil is dry. The glossy, dark-green leaves of summer are hard to resist, but you are in store for an even more stunning show in the fall of orange to scarlet and sometimes almost purple. Unfortunately, this tree can be a little hard to find because it is difficult to transplant. Look for plants that are small and container-grown. If you luck upon a large balled and burlapped specimen, make sure you ask if its roots were properly pruned in the nursery to ensure establishment and survival when planted.
Bald cypress, Taxodium distichum, also a native tree, is an extremely beautiful and adaptable tree. Many are reluctant to plant it because of the cypress knees that develop when growing in standing water or a consistently wet environment. These knees are not found when grown under normal soil conditions, as I can attest to, because I have one growing in my own back yard. I enjoy the soft green of summer, the rusty fall color in October, and the stately form and reddish-brown bark and branches in winter.

Buttonbush & spicebush shrubs
Buttonbush, Cephalanthus occidentalis, a native shrub, has glossy foliage that tends to emerge late but makes up for it by hanging on late into the fall. One of the most beautiful plantings I have seen is at Bernheim Arboretum, near Bardstown. The recently renovated King Fisher Pond was previously almost hidden but now has a beautiful garden with species suitable for wet sites around it. The most unusual characteristic of buttonbush is the flower. The creamy white flowers are about an inch in diameter and are more like a fluffy sphere than a button. They are subtle but beautiful and appear in late June, continuing to flower until early September.
Spicebush, Lindera benzoin, is a native shrub that prefers a slightly shady spot in which to grow. The flowers on this shrub are yellow, but only the females bear the scarlet fruit as it is dioecious. It is grown ultimately for its spicy aroma, which comes from all parts of the plant when brushed, bruised, or broken. I am particularly fond of the yellow fall color that glows from a dark shady spot in any garden.

Wildflower perennials
With perennials it seems there are even more to choose from. The native swamp sunflower, Helianthus angustifolius, and Joe-Pye weed, Eupatorium purpureum, are tall perennials and can reach heights of 5 to 6 feet. When the soils are dry these perennials will grow to only 4 to 5 feet tall.
The swamp sunflower is noted as being one of the finest fall flowering plants for our area. Unfortunately, it seems retailers concentrate on selling the traditional and overused "garden mum" or chrysanthemum, instead of promoting more of the reliably hardy fall-blooming perennials for the garden like swamp sunflower. This perennial spreads slowly in the garden, forming small mass plantings, and should be trimmed back slightly around the first of June. This will encourage denser, stronger growth to support the abundance of golden-yellow flowers that appear in early fall.
Joe-Pye weed is almost famous. It seems everyone recognizes this wildflower from the roadside as they travel around Kentucky in late summer and early fall. The large purple flower, 12 to 15 inches in diameter, can be even larger in fertile wet soil. It is actually made up of several flower heads coming together to make a truly impressive show. Eupatorium maculatum 'Gateway' is one that resides in my own very dry alley garden. This form is slightly smaller in habit with stems that are speckled purple and larger flowers that, to my eye, appear more pink than purple.
So if you live in an area that has wet and heavily compacted soil conditions, either due naturally or from an overflowing river bank, there is hope for a beautiful garden. The water may rise and fall as the rich river topsoil moves from one farm to the next, but the plants that survive and prosper afford us an opportunity to garden beyond our wildest dreams.