Tennessee Perennial Planting Guide: When and How to Plant for Your Zone
Perennials are plants that return every year․ Many gardeners think perennials are difficult to grow․ In fact‚ most perennials are very easy to grow once the right site is chosen‚ and the right plant is given a good start․ Most perennials, with a little planning and care, will bloom for a decade or more with relatively little effort․
Usually‚ gardening in Tennessee means planting in USDA zones 6b through 8a‚ depending on whether you live up in the mountains near the Virginia state line at Bristol‚ or down in the river valley by Memphis․ Planting times and plant hardiness will depend on your USDA zone․ Zone 4-9 will survive anything the state can throw at it․ Zone 8-10 may not survive a hard January freeze in Nashville or Knoxville․
When to Plant
September through mid-November are the ideal planting times for many perennials here in Tennessee because the soil is still warm from summer's growth‚ the air is cooler and therefore less stressful for the plant, and the roots have two to three months of growth before a winter dormancy sets in․ Come spring‚ that plant is ready to take off rather than spending its first season just trying to survive․
Spring planting‚ which is possible anytime between March and May‚ is arguably the second-best option‚ and honestly, what most people get used to doing, since that's when garden centers are stocked to the brim․ The downside of this timing is that your new perennial has to establish roots and start growing above ground before Tennessee summer hits․ That's more demanding on the plant․
Though not advised‚ if you do plant in July or August‚ be sure to water deeply (not just a surface sprinkling) two or three times a week‚ for at least the first month․ Container-grown perennials can dry out rapidly in 90-degree weather‚ so feel the soil one inch down‚ rather than simply looking at the top layer․
Site selection is more important than people think․
Before you dig a single hole‚ spend a week really watching your proposed planting area․ How many hours of direct sunlight do you get? Direct sunlight (that is not filtered) for six or more hours a day is preferred by most flowering perennials․ With fewer hours‚ go for shade lovers like hostas or hellebores rather than sun lovers like coneflower․
Drainage is another thing people skip and then wonder why their perennials are rotting at the crown․ Tennessee clay‚ especially in Middle Tennessee‚ is not the best drainage for something like a coneflower‚ dianthus‚ or lavender․ Test it: dig a hole about 1 ft (0․30 m) deep and fill with water․ If the hole doesn't drain after four hours‚ you have heavy clay and should amend with compost or use raised beds․
You might find that running a soaker hose along the base of your bed is the most efficient method of watering․ Sprinklers can lose water to evaporation‚ and they promote fungal diseases in plants' leaves․
How to Choose Perennials that Really Fit
After climate zone‚ next considerations are soil type and how much sun a garden area receives․ Some perennials are tolerant of the average heavy clay soils‚ like black-eyed Susan or daylily‚ while others‚ like lavender or blazing star‚ require sharp drainage and will sulk or even die in heavy‚ wet clay soils․
Don't just think about bloom time‚ either: hosta and ornamental grasses can be spectacular all summer long‚ something that can be a real advantage in a garden in Tennessee‚ where blooms don't last forever․ A garden containing only flowering plants may appear empty between October and March‚ but the use of perennials with showy foliage or seedheads can provide off-season interest․
And think about purpose․ For pollinators‚ coneflower‚ bee balm, and blazing star are reliable providers of food for bees‚ butterflies, and hummingbirds․ Good cut flowers for bouquets include black-eyed Susan‚ dianthus‚ and asters because they last long in a vase and readily flower again after being cut․
Standout perennials for Tennessee gardens․
Flowers of the black-eyed Susan are from mid-summer to early autumn․ It can withstand the heat of the Tennessee summer․ The black-eyed Susan is a hardy‚ clumping perennial that grows on its own from seeds․ It likes full sun․ One warning‚ however: while some varieties are true perennials that return every year‚ others are more like biennials or self-seeding annuals that will pop up again in subsequent years․
Dianthus offers colorful‚ fragrant flowers from spring to fall, depending on variety‚ in red‚ pink‚ white, and purple colors․ The flowers do tolerably well in Tennessee's clay soil as long as there is good drainage․ The blue-green foliage is attractive even when the plant is not flowering․
Blazing Star (Liatris spicata) is adored by pollinators․ It's a native wildflower‚ more tolerant of our humid summers than many native prairie plants․ It likes moist‚ organic‚ well-drained soil‚ but established plants do just fine during dry spells after its roots have established (well) in year 2․ In fact‚ they thrive․
Hostas deserve a mention here for any gardener who has shade․ And that's a lot of yards under Tennessee's mature hardwoods․ There's a hosta for every size and color of leaf, and they fill out those empty spots in shady beds when flowering perennials won't․
A Few Practical Notes
Mulch new perennial plantings with two to three inches of shredded bark or leaf mulch a couple of inches back from the crown to prevent rot‚ while also holding moisture and moderating soil temperature during that first summer․
The majority of perennials should be divided every three to four years‚ often when the center of the clump seems thin or at least when flowers are smaller than expected․ Early spring or fall is the best time for division․
TN Nursery ships perennials bare root from field nursery operations or in pots according to the species․ Starting with quality well-rooted plants makes a bigger difference than people expect․ Roots are a perennial's best friend at planting time‚ as these can get a plant through its first tough season‚ and into years of reliable return growth․
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