Gardening Sweet Spots
By Donna Hessel
Whether new to gardening or not, you’ve likely heard the advice to plant perennials because they come back every year. And maybe you’ve taken that advice and planted perennials, only to be disappointed that some didn’t show up the following spring, or they disappeared after a couple of years.
Well, it turns out that “perennial” doesn’t mean “forever.” It just means that the plant takes more than one year to complete its life cycle, unlike annuals that grow, bloom, set seed and perish all in one year. Short-lived perennials may live three to five years before they disappear. Long-lived perennials can be expected to live 10 years or more.
Of course, the plant tags don’t tell you that. And some plants sold as perennials are biennials, which sprout foliage the first year and flower the next; after which they perish. Those that are short-lived (three years) may reseed, but if you use weed preventer or accidentally pull the sprouts out for a weed, they are gone. Others may go dormant in the summer, resulting in an empty spot in your garden.
Coneflowers are one of the long-lived perennials
Most of shorter-lived perennials are long bloomers. Long-lived perennials tend to have a shorter season of bloom. This makes perfect sense botanically and biologically. Longer-lived plants are not tiring themselves out with reproduction — usually because a tap root or some other root adaptation provides their species endurance in a different fashion. Some of the shorter-lived perennials just need to be divided more frequently. Taking cuttings or divisions or multiply it by seed every two years will assure your short-lived perennial returns, year after year.
Coreopsis falls into the short-lived category
Some perennials considered long-lived die out in the center of the plant. Digging up the clump and replanting the outer portions will rejuvenate them and keep them where you want them. Perennials that have an extended blooming period, especially those that bloom in the fall, can be aided by removing some of the buds late in the season. This will allow the plant to put more of its energy into building a good root system and full crown, which will help it overwinter. Most perennials, other than bog plants, require well-drained soil over winter.
Some plants need a cold winter in order to grow well and bloom the following year. This process is called “vernalization.” It’s the process by which a plant goes dormant and is exposed to temperatures below 45 degrees F for a number of weeks – on average six to 10 continuous weeks of cold. A longer dormancy won’t hurt the plant and may help it recover more quickly in the spring. If your plant didn’t bloom, it’s possible that winter was not cold enough or long enough to accomplish vernalization. This may become an issue in our area with climate change.
The following table is an extremely helpful guide to short-lived, long-lived perennials and biennials. Notes on which plants are natives, as well which ones may reseed or need to be re-planted will help you decide which perennials will work best in your garden.
| Short-Lived Perennials | Native | Notes * indicates reseeding |
| Agastache *some | x | substitute Catmint or Liatris perhaps |
| Baby’s Breath (Gypsophila paniculata) | Try Calamintha nepeta for long-lasting cloud of white flowers | |
| Bee Balm (Monarda spp.) | x | more frequent division and replanting will keep it going |
| Blanket Flower (Gaillardia x grandiflora) | cut off buds near the end of the season to strengthen the roots and crown | |
| Blue Flax (Linum perenne)* | x | let it reseed |
| Blue Lobelia (Lobelia siphilitica) | x | substitute turtlehead in moist soils |
| Blue Vervain (Verbena hastata)* | x | let it reseed |
| Blue-eyed Grass (Sisyrinchium spp.) | x | |
| Brown-eyed Susan (Rudbeckia triloba)* | x | let it reseed |
| Cardinal Flower (Lobelia | x | substitute turtlehead in moist soils |
| Carnations, Border (Dianthus x alwoodii) | 2-3 years | |
| Columbine (Aquilegia spp.)* | some | hope for reseeding of these uniquely charming spurred spring flowers |
| Coral Bells (Heuchera spp.) | some | be sure soil is very well-drained, especially over winter |
| Delphinium | lives longer in cooler climates or with some shade in hot afternoon | |
| Foxglove (Digitalis spp.)* | allow to reseed and plant with some shade in hot afternoon | |
| Iceland Poppy (Papaver nudicaule) | lives longer in cooler climates or with some shade in hot afternoon; summer dormant | |
| Knautia* | Related to pincushion flower but usually in maroon shades; variegated cultivars showy | |
| Lupine (Lupinis × russellii)* | allow to reseed; resents heat and wet soil; huge flower spikes in a rainbow of colors | |
| Mallow (Malva spp.) | Long bloom season with usually pink or purple showy flowers in summer | |
| Maltese Cross (Lychnis chalcedonia)* | more frequent division and replanting will help to keep it going | |
| Mum (Chrysanthemum x morifolium) | tends to die out in center–dig up and replant outer sections as necessary | |
| Painted Daisy (Tanacetum spp.) | tends to die out in center–dig up and replant outer sections as necessary | |
| Penstemon | x | |
| Pincushion flower (Scabiosa spp.) | ||
| Pinks (Dianthus spp.) *some | ||
| Rose Campion (Lychnis coronaria)* | ||
| Shasta Daisy (Leucanthemum spp.) (other than ‘Becky) | tends to die out in center–dig up and replant outer sections as necessary | |
| Silene virginicum | x | |
| Tickseed (Coreopsis grandiflora, lanceolata)* | some | Plant ‘Zagreb’ or another strong C. vertillata cultivar instead; mildew a possibility on all |
| Wallflower (Erysimum linifolium) | ||
| Yarrow (Achillea spp.) | x | more frequent division and replanting will keep it going |
| Biennials | ||
| California Poppy (Eschscholozia) | ||
| Canterbury Bells (Campanula medium) | performs best in cooler climates or with shade in hot afternoon | |
| Clary Sage (Salvia | Gorgeous tall flower spikes and soft silver-green foliage–worth it even for one year! | |
| Dame’s Rocket (Hesperis matronalis)* | ||
| English Daisy (Bellis perennis) | Heavy bloomer in spring, red, white, pink | |
| Forget-me-not (Myosotis)* | prefers somewhat shaded woodland conditions; resents heat; early spring blue flowers | |
| Foxglove (Digitalis spp.)* | allow to reseed and plant with shade in hot afternoon | |
| Gloriosa Daisy (Rudbeckia hirta)* | Bigger flowers than regular B-ES, but must reseed to stick around | |
| Hollyhock (Alcaea rosea)* | should usually reseed, mostly tall cultivars with big cupped flowers lining stems | |
| Honesty (Lunaria)* | Seeds like crazy, keep it out of wild areas; silver dollar shaped seed pods | |
| Sweet William (Dianthus barbatus) | Big flower clusters in patterned pink, red, white; heavy bloomer with deadheading | |
| Verbena bonariensis* | usually will reseed; 4′ but a “see-through” plant; a few smaller cultivars available | |
| Summer Dormant Perennials | ||
| Bleeding Heart (Dicentra spectabilis) | Smaller fringe-leaved varieties do not usually go dormant, some native D. eximia | |
| Dutchman’s Breeches (Dicentra culcullaria) | x | |
| Virginia Bluebells (Mertensia virginica) | x | |
| Wood Poppy (Stylophorum diphyllum) | x | may go dormant if soil is dry in summer |
| Lupine | ||
| Oriental Poppy | ||
| Long–Lived Perennials | ||
| Lady’s Mantle (Alchemilla spp.) | Excellent foliage texture; small chartreuse flower clusters in spring | |
| Monkshood (Aconitum spp.) | Tall blue flower spikes; late summer-fall blooming; all parts toxic | |
| Peony (Paeonia spp.) | Relatively short blooming period but spectacular flowers and handsome foliage | |
| Liatris (spp.) | x | Nice summer color, grassy foliage and upright pink-purple flower spikes |
| Phlox | x | Provide excellent air circulation, keep foliage dry; choose mildew resistant cultivars |
| Japanese Anemone (A. hupehensis and hybrids) | Airy cloud of white or pink saucer-shaped flowers in fall; compact cultivars available |
| False Sunflower (Heliopsis spp.) | x | Yellow daisy shaped flowers in summer; most large plants in 3-4′ range |
| False Indigo (Baptisia spp.) | x | Compact cultivars still 3’x3′; early summer bloom in blue; white, pink, yellow cvs. avail |
| Astilbe | moist soil but must be well-drained in winter; fluffy plumes pink, red, white in summer | |
| Iris, bearded (I. germanica) | Amazing flowers in rainbow colors; reblooming cultivars available | |
| Iris, Siberian, Japanese, Louisiana | For moister soils; purple, blue, black, white, yellow, deep red | |
| Poppy, Oriental (Papaver orientale) | Foliage goes dormant after flowering and reappears in fall; early summer bloomer | |
| Poppy, Iceland (Papaver nudicale) | Early spring bloomer; orange, yellow, pink; does not like heat and humidity | |
| Coneflower, Pale Purple (Echinacea pallida) | x | pale lavender with narrow recurved petals; taprooted |
| Coneflower, Narrow-leaved (Echinacea angustifolia) | x | pale lavender with narrow recurved petals; taprooted |
| Butterfly Weed (Asclepias incarnata, A. tuberosa) | x | incarnata for moist soils, tuberosa well drained a must; monarch food source |
| Turtlehead (Chelone glabra) | x | Moist to wet soil, pink or white flower |
| Ironweed (Vernonia spp.) | x | Tall, pink flower spikes, excellent pollinator |
| Daylily (Hemerocallis spp.) | choose rebloomers for longer flowering period–“Stella” series; buds/flowers edible | |
| Hosta | Keep “blues” out of the sun; some yellows can take more sun | |
| Stonecrop (Sedum spp.) | Well drained soil a must; colorful foliage; some evergreen | |
| Catmint (Nepeta spp.) | Most with fragrant foliage; cut back after 1st bloom for 2nd flush | |
| Aster (Symphyotrichum novae-angliae) | x | Fall bloomer pink, white, blue, purple |
| Agapanthus | Limited hardiness, blue sphere of flowers with grassy foliage | |
| Goatsbeard (Aruncus dioicus) | Big plant with panicles of creamy white | |
| Gas Plant (Dictamnus albus purpureus) | Big plant with pink flower spikes | |
| Carolina Lupine (Thermopsis villosa) | x | Yellow flower spikes; large growing; relatively short blooming period |
| Red-hot Poker (Kniphofia spp.) | x | no wet soil in winter; smaller cultivars available |
| Bugbane (Cimicifuga spp., syn. Actaea) | some | A. elata, A. racemosa natives; several cultivars with black/purple foliage |
| Hellebore | evergreen shade plant; blooms in winter/early spring | |
| Perennial Geranium (Geranium spp.) | x | good groundcover for dry shade; pink, blue, white flowers |
| Lungwort (Pulmonaria) | fuzzy silver patterned green leaves; watch for mildew; spring bloom | |
| Balloon Flower (Platycodon spp.) | summer bloom, blue, pink, white flowers; most under 1′ tall | |
| Most Grasses & Ferns | some |
General Tips for Growing Perennials
Where to plant. Consider the amount of light available to the area in which you wish to plant. Most plant tags list the plant’s sun or shade requirements. Six-plus hours of full sun are required for full sun plants; part sun/part shade plants require four to six hours of direct sun exposure per day. Full shade plants need less than four hours of direct sun per day. After your plants are growing, take a look at them. If the edges of their leaves are turning brown, they might need more shade or water. If they are leaning towards the sun or not producing many flowers, they may benefit from being moved to a brighter location.
Watering: Grouping plants together by their watering preferences makes it easier to provide the amount of water plants need. Plant labels often include “drought resistant” for plants that don’t need a lot of watering.
Deadheading: Removing spent flowers from a plant before it goes to seed will encourage some plants to bloom more. If you choose not to deadhead, it won’t hurt the plant. When you choose to deadhead, cut the stems by about one third or to the top of the mound of foliage. If the plant is producing small buds along a stem, cut to the top of the next bud. Some plants such, as false indigo (Baptisia), coneflower (Echinacea), clematis and ornamental grasses, develop interesting seed heads if you don’t deadhead them, providing winter interest in your garden.
Fertilizing: Perennials don’t need as much fertilizer as annuals. Spreading a thin layer or scattering compost, humus, manure, shredded leaves, worm castings or other organic ingredients on top of garden beds in the spring will provide natural fertilizer, as worms and rain work them into the soil. Using a slow-release plant food formulated for perennials in spring and summer will increase soil nutrition.
Cutting back in autumn: The choice to cut perennials down in the fall or not is yours. You may want to cut plants you do not want to reseed. Any plants with diseased foliage, such as powdery mildew, rust or leaf spot should be cut to the ground and cuttings trashed (not used for compost). Plants damaged by insects that may have deposited eggs in the plants should be removed.
Evergreen or semi-evergreen perennials should not be cut back in the fall. Don’t cut back perennials with woody or hollow stems, or those with winter interest that will benefit wildlife, such as ornamental grasses.
Dividing: As a general guideline, perennials should be divided in the opposite season of which they bloom. If they bloom early in the season they should be divided in fall, and if they bloom late, they should be divided in spring. When you divide them, dig up the whole clump of the perennial you want to divide so you can easily see its root system. Each piece you pull or cut away from the original clump should be no smaller than what would fit in a 1-quart (4-6”) pot. Immediately replant the divided pieces into the garden or containers before their roots dry out. It is best NOT to divide plants with woody crowns, a single stem/crown, fragile fleshy roots, or a tap root, as doing so can damage the plant.
Mulching: Your perennials will benefit from having mulch around their roots year-round. Organic mulch like shredded bark, hardwood, or pine straw serves several useful purposes as well as making your garden look cared for and neat. Mulching plants will keep the soil cooler and roots healthier, help to retain soil moisture longer, prevent weeds from growing and will add nutrients to the soil as it disintegrates. If you plant perennials or shrubs in the fall, a three- to four-inch layer of mulch around them will prevent heaving from freezing/thawing soil over winter months.
Finding out that my perennial plants are probably not going to last forever was a wake-up call for me, and I’ve been gardening for years. Always something new to learn! I will definitely be referring to the chart included here before I add plants to my garden in the future.
Article Sources: Garden Artisans Online Newsletter,“Not So Perennial Perennials” (including perennial chart), posted on Jun 03, 2022 by Kerry Kelley.
Proven Winners Online Newsletter, “Tips for Maintaining Perennial Plants,” June, 2022 by Kerry from Proven Winners
Main photo courtesy bigstock.com; embedded photos courtesy pexels.com.
