How to Grow Big‚ Bold Perennials That Actually Perform
The key to successfully using this flashy‚ spectacular perennial is knowing where to put it and then giving it two years in its new home․ Most of us throw in the towel after the first summer‚ when the perennial doesn't have enough roots to support all that top growth․ With a little foresight and a few good early choices‚ you can go from 18-inch stragglers to 4-foot showstoppers․
All of Tennessee is located in USDA zone 6b to 8a‚ with the warmest areas in the metropolitan areas of Memphis and Chattanooga and the coolest areas in the higher elevations west of Johnson City and north of Elizabethton․ One can combine big perennials requiring considerable chill (such as peonies and delphinium) in the interior zone with heat-loving bruisers such as Joe Pye Weed and Rudbeckia which will not thrive farther north or south․
Choose perennials that actually get big
What they don't tell you is that plants don't have set sizes․ A 3 foot tag means 3 feet at optimum growing conditions․ Gardens are far from ideal․ Heavy clay soil and up to 30% canopy shade in the dry season has been shown to decrease maximum size by over half․
Heavy Tennessee sticky red clay holds the winter moisture like a sponge‚ rotting the crowns of lavender‚ Russian sage‚ or‚ for that matter‚ most anything else before they ever got large․ And yet‚ moisture-loving behemoths like Joe Pye Weed‚ ligularia and hardy hibiscus do just fine‚ while they would sulk in well-drained sandy soil․
Few waterfalls in Tennessee are as large or as spectacular as:
Hardy Hibiscus - This is probably the single best "instant impact" perennial for the Southeast․ Hardy Hibiscus dies down to nothing every winter‚ but by midsummer it will be 4 to 6 feet high and covered with dinner-plate sized white‚ pink‚ or red flowers․ It grows in full sun in wet places such as low spots in lawns or other places not covered by another plant․
Joe Pye Weed - A huge plant‚ like a weed in your woods and creek bed‚ sometimes 5 to 7 feet tall in a good spot in Tennessee‚ with dusty pink flowers that bring dozens of swallowtails and monarch butterflies․ This is not a border plant․ Avoid it like the plague․
The peony is well suited to the Tennessee climate‚ as its cold winter gives the plant enough time to chill and bloom in the spring․ It is‚ however‚ much less easily grown in the South; if there is a flower in the first and second years there are many flowers in the third or fourth year․ Peonies require full sun and well drained soils‚ particularly over winter․
Echinacea (Coneflower) - Will establish well and is very drought tolerant‚ once established․ Heads should not be deadheaded in the fall since it will set seed profusely․ Great for filling in beds․
Ligularia - For the shade or moist places - large coarse foliage and spikes of yellow-orange flowers give an almost tropical effect․
Delphiniums‚ I love them․ But they are very fussy if you want to do it here in Tennessee‚ where the summer weather is quite humid‚ and with a little drainage problem they will rot․
Preparing the Soil (This Is Where Most Gardens Fail)
If your soil is too moist (most middle tennessee clay seems to do it)‚ you may need to take the bed up 4 to 6 inches more‚ and add even more topsoil and compost․ Peonies and delphiniums will rot in wet soil․ Moisture loving perennials like Joe Pye Weed and hibiscus do well with some drainage as well․
The fall makes sense too: dormant rootstock planted in fall (September to maybe mid-October‚ most of Tennessee) have 4-5 months to root into cool moist soil before the heat of summer shuts them down․ Plants planted in the fall do much better in year two․ You can even plant in spring‚ but you will have to water very well that first summer because the roots won't be established yet․
Where plants are of similar mature dimensions (for example‚ space space hardy hibiscus 3 feet (0․91 m) apart)‚ three to five of the same species together may look better than one plant of a species at respective intervals on each of the four sides․ Too close together‚ plants may become deformed and suffer powdery mildew․
However‚ this requires taking an active care․
Big thirsty plants need big food too‚ so apply slow-release balanced fertilizer at the start of the growing season early in spring before leaf-out in spring and again mid-summer for big flowering shrubs such as hibiscus․ Take care not to over fertilize; a little is good‚ more is not necessarily better․ Since the new growth will be killed by frost before maturing‚ fertilizing should no longer occur after August․
Water deep (one to two times a week) instead of shallow (one time a day) so that the roots will grow down when watered deep․ Use a two-inch layer of mulch to hold in moisture in Tennessee clay soil and to keep the clay from hardening in the July sun․
Deadhead echinacea and hibiscus to encourage a second bloom․ Leave coneflower heads in the fall to self-seed and feed goldfinches in winter․ In any case plants need dividing every 3 or 4 years‚ as the mounds become too crowded (before the woody cores develop in summer)․
A TN Nursery field grown plant with its root system tuned to your native soil and your native climate is miles ahead of a small greenhouse plant (especially if you are starting from scratch in a new project)․ The difference can be the difference between a perennial sulking along its first year and one putting on bulk in its first full summer․
Give them place and a good soil‚ and leave them alone for two seasons‚ and you will be surprised․
