Fall care of perennials․
Winterizing perennials involves watering less frequently and more deeply‚ then adding fresh mulch‚ removing litter from around the plant‚ and finally covering it with frost cover when the temperature first drops to the low thirties F in the fall․ If timely and properly done from September through the end of November‚ these four steps will improve most plants' spring returns in Tennessee Zone 6b-7b․
This is when the real work begins for your perennial plants․ There's a lot you can do (and not do) between now and the first hard frost to ensure that your coneflowers‚ hostas‚ daylilies‚ and other perennial flowers will survive the winter and pop up again next April․ Here's some information you might want to know․
Water: Less Frequent‚ Deeper Soaking
Although perennials need less water during their dormant winter period‚ calendar watering is not recommended‚ as the flower roots continue absorbing water and energy year-round while the above-ground growth has ceased in the fall season․
In Middle Tennessee‚ first frost usually occurs between October 15 and November 5․ Water can be applied deeply‚ every 10 to 14 days in September and October․ In the final 3 to 4 weeks of the growing season (into end November) water every 2 to 3 weeks if no rain‚ deep enough to be 8 to 10 inches deep to minimize winter heaving and winter damage․ A short‚ surface sprinkle‚ however‚ teaches roots to stay at the surface‚ where they are more prone to freeze and thaw․
Do not water once the ground begins to regularly freeze‚ typically in late November to early December across most of Tennessee․
Mulching is your single best investment this season
If you do nothing else this fall‚ mulch․ A 2 - 3 inch layer of shredded bark‚ straw or chopped leaves around base of perennials helps moderate soil temperature‚ keep soil moisture and lessen soil heaving from freezing and thawing that can push shallow roots right out of the ground․
Timing is also important․ Don't mulch until the soil has cooled down (a couple of light October frosts will do)‚ for that early growth will die in the inevitable cold snap to come․ When night time temperatures are consistently in the 30s‚ mulch each plant thickly‚ but keep an inch or so of air space around the plant's crown to prevent rot․
We keep a good supply of pine straw or shredded hardwood mulch for this purpose‚ and either one makes a terrific addition to your Tennessee garden‚ depending on whether you want the woodier‚ less formal look of pine straw‚ or the denser look of a shredded hardwood mulch․
Fertilizing: Ease Off‚ Don't Cut Off Completely
Fertilizing with a high nitrogen fertilizer in the fall is usually not appropriate‚ as it produces foliage growth during a time when the plant is preparing for dormancy․ If there is severe nitrogen deficiency‚ then a slow release low nitrogen fertilizer can be applied in early September‚ to be released slowly during the dormant season․ By October‚ these plants may be allowed to go dormant without fertilizer․
Pruning and Deadheading: Be Selective‚ Not Aggressive
Deadheading spent flowers of repeat-flowering perennials such as coneflower or salvia may encourage one final flowering before frost; however‚ heavy pruning is seldom necessary in fall․
Although experts recommend against doing so‚ most perennial plants‚ including ornamental grasses‚ sedum‚ coneflowers‚ black-eyed Susans and a dozen others‚ do better in winter if left to stand․ They provide food for wild birds‚ the hollow stems are nesting shelters for native‚ solitary bees‚ and they add interest to the winter garden when their skeletal remains are standing․ The only pruning normally conducted is a major cutback in late winter or spring․
Exceptions are: powdery mildew on bee balm‚ black spot on a few perennials‚ and rust in hollyhocks․ Such plants may need to be cut back to ground level and the debris removed rather than composted‚ as fungal spores can survive in plant debris from one year to the next․
Pest and Disease Cleanup
You're also going to want to walk your beds for yellow leaves‚ spots‚ or sticky goo in late September or early October‚ as you're better off getting those issues taken care of now․ Aphids‚ spider mites‚ and spores of fungal pathogens can withstand mild winters in the leaf litter of Tennessee and become active again in spring․
Be sure to rake away fallen leaves and dead growth from plants․ A thin layer of leaves at the base of healthy plants helps them‚ but do not strip every bed bare․
Protection from frost for tender varieties
Not all perennials can survive the winter in East Tennessee․ The USDA Hardiness Zone ranges from Zone 6a‚ in the mountains at higher elevations‚ to Zone 7b‚ around Memphis․ In East Tennessee‚ tender perennials (such as cannas‚ some salvias‚ and some tropical hibiscus) must be covered on frost nights if they are expected to persist as perennials (and uncovered in the mornings)․
Container-grown perennials do best left in an unheated garage or shed‚ provided that the temperature is maintained in the mid-20s; plant roots in containers are more at risk of freezing than those in the ground‚ as they do not benefit from a mass of soil around them․
Dividing and Transplanting
Oddly‚ the best time to dig and divide crowded perennials such as hostas‚ daylilies and irises is fall‚ or September and October‚ when divided plants have six weeks to develop new roots before the ground begins to freeze․ Transplanting in the cooler fall weather causes less shock than at summer's end or late spring when it is still hot at night․
Water the new plants as you plant to firm the soil against the roots‚ and to eliminate air pockets․ If you fill gaps in flower beds with perennials‚ fall is the best time to plant to give them a head start․ Perennials planted in autumn typically overwinter better and grow better in spring than those planted in spring․
TN Nursery provides a broad selection of bare root and potted perennials such as coneflower‚ black-eyed Susan and our native asters that are perfect for fall planting․ September through November is the best time to install these beautiful flowers․
Watch the Weather Forecast Closely
It may be 75 degrees one week and have a hard frost the next․ Check the weather forecast periodically through the beginning of October and all through November to see what effect it may have on your schedule․ A little mulching and protection from winter damage almost always limits the occasional disaster when a plant that should sail through does not․
