What Are Perennial Plants and How to Care for Them
These perennials die back to the ground in the winter months and grow back from their root system each year․ This is because they have a root system that lasts for three or more years․ Unlike annuals and biennials that must be replanted each year‚ perennials have established roots that come back for you year after year․ In Tennessee‚ from the high places in the far eastern part of the state with a low of Zone 6b‚ to the western side of the state with a low of Zone 7b‚ perennials are the foundation of any no fuss garden․
Let's be frank: plant a coneflower or a daylily‚ and you will be dividing it and giving starts away every four or five years․ Nothing could possibly have a better annual return on investment․
Differences between perennials‚ annuals‚ and biennials
Annual plants grow from seeds‚ flowering‚ setting seed and dying in one growing season․ Biennials take two seasons to complete their life cycle‚ flowering in the second․ Perennial plants will not die‚ but they will most likely go dormant in winter; the foliage may die back completely and the plant and its crown and rootball will continue to be stored energy underground until the soil warms up․
It's why you don't see Nashville or Knoxville gardeners scraping bare ground where they planted black-eyed Susan last summer‚ then a few days later‚ watching it return every April with the regularity of a railroad schedule․ Dormant‚ predictable dormancy is good․
Perennial Planting in Tennessee Gardens
Not every perennial plant that grows well in Vermont would do well during the summer in Memphis and vice versa‚ but there are three factors that determine the range of plant species․
Hardiness zone: The majority of Tennessee is in zones 6b and 7b․ Perennials rated for zone 4 through zone 8 should survive winter cold snaps and summer heat in the state․ When purchasing these plants‚ it is always good to check the tag because some of the perennials are only rated to zone 8 and not appropriate for a hard winter on the eastern mountains․
Soil type․ Clay-rich Middle Tennessee soils retain water differently than some West Tennessee areas where sandier‚ more acid soils are found․ Coneflowers‚ black-eyed Susans‚ and daylilies all grow well in clay soil․ Avoid plants that do not prosper in wet soil or require good drainage‚ such as lavender․
Sunlight․ Track how many hours of sun a bed actually gets before you buy․ March sun may become June shade as trees fill out‚ so full sun perennials need 6 or more hours of sunshine per day‚ while shade perennials are content with filtered sun or morning sun․
TN Nursery's available collections of coneflowers‚ daylilies‚ and black-eyed Susans include plants that are well-suited to the clay-based soils and humidity that characterize many gardens throughout the state of Tennessee․
Planting: Timing and Technique
They are best planted in fall and early spring․ Fall planting between September and early November allows for the roots' establishment in cool‚ moist soil before dormancy․ Trees planted in the fall grow hardier in the spring than ones planted in spring․ You can also plant in the spring‚ after your last frost date: April 1-15‚ depending on your region of the state․
Its best to dig a hole twice as wide as the root ball‚ and not deeper․ The most common mistake is planting too deep‚ which smothers and rots the crown․ Plant the stem where it stems from the root‚ at or just above the soil level․ Backfill‚ water well‚ and do not fertilize at this stage․ The fertilizer will burn the roots․ Let the roots settle for two to three weeks․
Watering Realities
Newly installed perennials should be watered until established (six to eight weeks)․ The soil should be kept evenly moist‚ 1 inch of water a week from rain or hose․ Surprisingly‚ most perennials are quite drought tolerant once established․ Once established‚ coneflowers and daylilies can survive the two to three weeks of summer drought that Tennessee can experience․
Exceptions are plants near midsummer (July and August) where established perennial flowers may need a deep drink once a week․ Water at ground level‚ never overhead‚ to avoid fungal diseases in hot‚ humid conditions․
Mulching That Actually Helps
During dry weather‚ put down a 2-3 inch layer of shredded bark mulch‚ or pine straw․ A good mulch helps keep weeds from competing with your plants for water and nutrients․ Try to leave 1-2 inches of space between ground and plant crown; mulch resting on the stem will generate crown rot in hot‚ wet summers that are common in our area․
Feeding Your Perennials
Once they are in place‚ most perennials need little or no extra fertilizer․ A slow-release balanced fertilizer worked into the soil as the new growth begins in early spring is adequate for most plants․ Alternatively‚ a 2-inch layer of compost yearly worked into the soil each fall works as well and has the added advantage of improving Tennessee's clay-laden yard each year․
Flowering perennials do not thrive with high-nitrogen fertilizers‚ which favor leaf growth rather than flowering․
Deadheading and Pruning
Deadheading extends the flowering period by preventing the plant from expending energy on making seeds․ This is done by trimming the stem just above the next healthy leaf or bud․ For example‚ coneflowers and black-eyed Susans may flower a second time in late summer‚ if deadheaded repeatedly in June and July․
Some perennials such as catmint will become leggy and will need to be cut back by up to 50% in early summer; others do not need pruning except to remove damaged leaves and stems․ Some plants‚ for example‚ coneflowers‚ should be left with their flower heads in fall to serve as food and structure for birds and a winter landscape․ The plants should be cut back to a few inches above the ground as growth begins again in late February․
Pest and Disease Watch
Check plants every two weeks during the growing season for aphids‚ spider mites‚ and powdery mildew․ Powdery mildew is most common in humid conditions․ Good air circulation and space between plants will reduce most fungus problems․ Insecticidal soap will control most soft-bodied insects‚ but is pollinator-safe․
Getting Through Winter
The foliage dies back after the first hard frost; a mulch may be applied around the crowns of borderline hardy perennials in the zone we grow in․ Some gardeners cut down the vegetation in autumn‚ while others prefer to leave the vegetation in place until the last week of winter‚ when the vegetation provides a protective cover for overwintering helpful insects․ Either is valid and it is up to the individual gardener to do what works best․
Of all the plants in the garden‚ perennials are probably those which best reward the gardener for his patience in waiting the season or two for them to settle in․
