To help gardeners and farmers determine what plants they can grow where they live, the U.S. Department of Agriculture divides the country into 11 plant hardiness zones. A USDA zone is an indication of how cold a winter a perennial plant – a species that can survive for more than one growing season – can tolerate. The majority of Kentucky is in USDA zone 6, though the westernmost part of the state lies in zone 7. The state is home to more than 2,500 plant species that include many different types of trees and wildflowers.
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Plant Zones in Kentucky
Perennial plants in zone 6 can handle temperatures between -10 and 0 degrees Fahrenheit. Zone 6 is further divided into zones 6a and 6b, which have a five-degree difference. Perennials suited for zone 6a are capable of surviving temperatures between -10 and -5 degrees Fahrenheit. Those that are hardy to zone 6b can withstand temperatures between -5 and 0 degrees Fahrenheit. In zone 7, where the southwestern tip of Kentucky is located, temperatures rarely drop below 0 degrees Fahrenheit. If a plant is hardy to zone 7, that means it can handle temperatures between 0 and 10 degrees Fahrenheit.
Native Kentucky Trees
The forests of Kentucky are home to some 120 species of trees. The state tree of Kentucky is the tulip tree (Liriodendron tulipifera), a deciduous species that can grow anywhere between USDA zones 4 and 9. It produces cup-shaped flowers in May and June, hence the tree's common name. Other deciduous trees – those that shed their leaves in winter – that grow in Kentucky include maples, birches, hickories, oaks and magnolias. The American sycamore (Platanus occidentalis), which is hardy in USDA zones 4 to 9 and is considered the largest tree in eastern North America with a height of 100 feet, also occurs naturally in the forests of Kentucky.
The state's USDA zone 6 trees also include 10 species of conifers, which are evergreen trees with needlelike leaves that produce cones. Kentucky's conifers represent three families: pine, cypress and yew. The only nonevergreen conifer in Kentucky is the swamp-dwelling bald cypress (Taxodium distichum), which changes colors in the fall and sheds its leaves.
Kentucky Flowers and Grasses
There is great diversity of wildflowers in Kentucky. They include the bloodroot (Sanguinaria canadensis), which produces white flowers. The common name of the species refers to the plant's crimson-colored root, or rhizome, which can be squeezed to extract a red liquid that is used as a dye. Bloodroot is an early bloomer, with flowers appearing in late winter and into spring.
On the other hand, the state flower of Kentucky, the goldenrod (Solidago gigantea), an herbaceous perennial hardy in USDA zones 3 to 8, produces yellow flowers from August to October. The goldenrod is found in 47 of the 48 contiguous states, with Arizona being the exception. Other perennial wildflowers that occur in Kentucky include sunflowers, Virginia bluebells, milkweed, phlox, indigo and coneflowers – a genus that includes the iconic black-eyed Susan.
- United States Department of Agriculture: USDA Plant Hardiness Zone Map
- Missouri Botanical Garden: Liriodendron tulipifera
- University of Kentucky College of Agriculture, Food and Environment: Common KY Trees
- Better Homes & Gardens: How to Use Hardiness Zone Information to Figure Out What You Can Grow
- The Arboretum State Botanical Garden of Kentucky: Conifers of the Walk Across Kentucky
- HGTV: Plant Hardiness Zones
- Missouri Botanical Garden: Platanus occidentalis
- Oldham County Cooperative Extension: KY Spring Native Flowers
- Missouri Botanical Garden: Solidago gigantea
- University of Kentucky Cooperative Extension Service: Wild about Wildflowers