Growing Perennials

Herbaceous perennials generally live for three or more seasons, but usually the tops die back to the ground each fall. The crown and roots of the plant resume growth in spring. A few perennials are evergreen or keep a green rosette of leaves at the base in winter. Hardy perennials can live through the winter without protection.

Many plants, such as cannas and dahlias, are hardy perennials in South Carolina that will not live through the winter outside farther north. On the other hand, many of the perennials that grow well in the Northeast United States or England will not tolerate hot, humid summers. Since books about perennials are often written for those cooler climates, it is important to use care in selecting plants that are adapted to Southern heat and humidity.

Ornamental Features

Perennials provide year-round color and interest, with endless variations in colors, sizes, habits and time of bloom. Although some perennials flower for only a few weeks, the ever-changing color display forms much of the excitement of a perennial garden. Many perennials will re-bloom in the warm climate of South Carolina.

Some perennials, such as ferns and hostas, are grown principally for their beautiful foliage. Include foliage plants to extend seasonal color and texture in the garden.

Landscape Use

While the traditional English perennial border was entirely made up of herbaceous perennials, they are attractively used in combination with other plants in the total landscape. Perennials are easily used as ground covers, mixed with annuals, grown in containers, and used as accents or specimen plants.

There are perennials for full sun, part-sun, or heavy shade, and for dry, moist, or wet soil. Select perennials that are suited to the growing conditions where they will be planted. Select a planting area with good air circulation to help avoid diseases.

Soil Preparation

Good soil preparation is extremely important for growing perennials, since they may be in place for many years. Deeply spade the beds to a depth of eight to 10 inches. Amend clay soils by mixing in at least 2 inches of composted pine bark, composted leaf mold, or a pine bark-based soil conditioner to improve the soil drainage and aeration. Improve water retention in sandy soils by mixing in 2 to 3 inches of composted leaf mold, peat moss, manure, or a peat moss-based potting soil. Good soil drainage is critical to the success of most perennials. Raised beds can be used to ensure adequate drainage.

Base fertilizer and lime applications on the results of a soil test for best results. In the absence of a soil test, add either a complete fertilizer such as 10-10-10 at the rate of 1 pound per 100 square feet of bed area, or add either a complete slow-release fertilizer or complete organic fertilizer following label directions. In coastal counties, such as Horry, Charleston, and Beaufort, that have soils with more than adequate phosphorus, use ¾ pound of a 15-0-15 fertilizer per 100 square feet of bed area. For most fertilizers, a pint is a pound.

A pH of 6.0 to 6.5 is ideal for most perennials. Most South Carolina soils are very acidic (except for some areas along the coast) and require the addition of lime to correct pH. In the absence of a soil test, add 4 pounds of pelletized lime (3 pints) per 100 square feet of bed area. Incorporate lime and fertilizer into the top 4 to 6 inches of soil after mixing in the soil amendments. Rake the soil surface smooth. For more information about how to test the soil, please see HGIC 1652, Soil Testing.

Planting

Most perennials should be planted in the fall or early spring. Fall planting gives the plant more time to become established before the start of active growth in the spring. Fall-planted perennials are usually well-established before hot weather. Fall planting should be finished at least 6 weeks before hard-freezing weather occurs.

Early spring is also considered a good time to plant perennials. Planting early, just after killing frosts have passed, is better than later spring planting.

Many perennials can be grown from seed, but most gardeners prefer to start with established plants. Perennials are available grown in containers, field-grown, or shipped bare-root and dormant.

If plants are somewhat pot-bound at planting time, loosen the roots around the bottom and sides of the root ball and spread them out in the bottom of the planting hole. To encourage side root growth, make the hole twice as wide as deep. Refill the hole, firming the soil in around the plant to avoid air pockets. Be sure the crown of the plant (the point where roots and top join) is even with the soil surface.

Watering

Water the new perennials thoroughly following planting to settle the soil around the roots. Pay especially close attention to watering the first few weeks while plants develop their root systems. Adequate moisture is essential for the growth of perennials. Most perennials require at least 1 to 1½ inches of water per week from rain or irrigation. More may be needed during very hot weather.

To promote deep root growth, water thoroughly and deeply. Allow the soil surface to dry before watering again. Soaker hoses and drip irrigation are ideal watering methods since they save water and avoid wetting leaves and flowers.

Mulch perennials with a 1- to 2-inch layer of compost, pine bark or pine straw to help keep down weeds and conserve moisture. Avoid overly heavy mulching to help prevent crown rot.

Maintenance

Weed control should usually be done by hand-weeding or with the use of herbicides to avoid damaging shallow roots. Read and follow label directions before using any herbicide. Do not apply pre-emergence herbicides around newly planted perennials, as these products will stop root growth.

Maintenance fertilization should be based on the results of a soil test. In the absence of a soil test, apply a complete, slow-release fertilizer, such as a 12-6-6, at the rate of 1 to 2 pounds per 100 square feet of bed area just before new shoots emerge in the early spring. For additional growth, repeat the fertilizer application in 6 weeks. Alternatively, complete organic fertilizers may also be used. However, if a soil test reveals that the soil pH is above 6.5, use an acid-forming, complete fertilizer instead, such as an azalea & camellia fertilizer, or use an acid-forming, complete organic fertilizer. Avoid touching any emerging leaves with fertilizer to avoid leaf damage. Alternatively, apply 4 to 7 pounds of a complete organic fertilizer, such as Espoma Garden-tone (3-4-4) per 100 square feet.

Many newly planted perennials will not bloom the first year. A few, such as peonies, may take several years to bloom heavily.

Many perennials should be staked to prevent them from bending or falling over during wind and rain. When staking is done correctly, the plants grow to cover the stakes. A floppy perennial plant may be an indication that the plant is not receiving adequate sunlight and needs to be relocated.

Remove old flowers to encourage re-bloom on perennials. Many perennials should be cut back to ground level after bloom is finished to encourage new leaf growth from the base.

Remove dead foliage and stems in the fall, and mulch to protect crowns and roots from alternating mild and freezing weather.

Most perennials eventually become overcrowded and require division. Information on division is available in HGIC 1150, Dividing Perennials. Many perennials are also easily propagated in this way. Other methods of propagating perennials include stem cuttings, root cuttings and seed.

Problems

Perennials vary considerably in their susceptibility to pests. Selection of resistant species and cultivars, proper site selection, and good cultural practices will prevent many disease problems.

Perennials for Various Uses

Many perennials are available in several cultivars with different color, height or other attributes. Some, such as the heat-and humidity-tolerant cultivar of lamb’s ears called ‘Big Ears,’ are better suited to our climate than the species. Consult with a local nursery person or Extension specialist for cultivars that are especially suited to your area.

Perennials for Shade

Those marked with a * will tolerate the most shade.

Acanthus mollis – Bear’s Breech

Alchemilla mollis – Lady’s Mantle

Amsonia tabernaemontana – Blue Star

Anemone species

Aquilegia species – Columbine

Arum italicum – Painted Arum *

Asarum species – Wild Gingers *

Please see HGIC 1113, Wild Ginger

Aspidistra elatior – Cast Iron Plant *

Astilbe x arendsii – Astilbe

Begonia grandis – Hardy Begonia

Bergenia cordifolia – Heartleaf Bergenia

Brunnera macrophylla – Siberian Bugloss

Carex elata – Golden Sedge

Ceratostigma plumbaginoides – Plumbago

Please see HGIC 1180, Perennial Leadwort

Chasmanthium latifolium – Upland River Oats

Chelone obliqua – Turtlehead

Chrysogonum virginianum – Green and Gold

Please see HGIC 1186, Green & Gold.

Cimicifuga species – Bugbane

Convallaria majalis – Lily-of-the-Valley *

Cyclamen species – Hardy Cyclamen

Dicentra species – Bleeding Heart

Digitalis species – Foxglove

Epimedium species – Barrenwort *

Ferns * (most)

Please see HGIC 1176, Hardy Ferns

Galium odoratum – Sweet Woodruff *

Geranium maculatum – Wild Cranesbill

Gillenia trifoliata – Bowman’s Root

Helleborus foetidus – Bearfoot Hellebore

Helleborus x hybridus – Lenten Rose

Please see HGIC 1185 Lenten Rose

Hexastylis species – Gingers

Please see HGIC 1113, Wild Ginger

Heuchera species & hybrids – Coral Bells

Hosta species – Plantain Lily

Please see HGIC 1165, Hosta

Iris cristata – Dwarf Crested Iris

Please see HGIC 1167, Iris

Lamium maculatum – Spotted Dead Nettle *

Lobelia cardinalis – Cardinal Flower *

Lobelia siphilitica – Great Blue Lobelia *

Mertensia virginica – Virginia Bluebells *

Myosotis sylvatica – Forget-me-not

Phlox divaricata – Woodland Phlox

Phlox stolonifera – Creeping Woodland Phlox

Polygonatum species – Solomon’s Seal *

Primula species – Primrose

Pulmonaria species – Lungwort *

Salvia koyame – Japanese Yellow Sage

Saxifraga stolonifera – Strawberry Begonia

Shortia galacifolia – Oconee Bells *

Sisyrinchium angustifolium – Blue-Eyed Grass

Smilacina racemosa – False Solomon’s Seal

Spigelia marilandica – Indian Pink

Please see HGIC 1188, Indian Pink

Thalictrum species – Meadow Rue

Tiarella species – Foam Flower *

Please see HGIC 1183, Foam Flower

Tradescantia virginiana – Spiderwort *

Tricyrtis species – Toad Lily *

Trillium species – Wake Robin *

Viola species – Violet *

Tolerant of Moist or Damp Soils

Those marked with a * will tolerate wetter soils.

Acorus gramineus – Sweet Flag *

Amsonia tabernaemontana – Blue Star

Aster novae-angliae – New England Aster

Astilbe x arendsii – Astilbe

Canna species – Canna *

Carex species – Sedge *

Chelone species – Turtlehead *

Cimicifuga species – Bugbane

Colocasia esculenta – Elephant’s Ear *

Crinum species – Milk and Wine Lily, Crinum

Cyperus alternifolius – Umbrella Sedge *

Eupatorium purpureum – Joe-Pye Weed

Ferns, many

Please see HGIC 1176, Hardy Ferns

Filipendula species – Meadow Sweet

Galium odoratum – Sweet Woodruff

Helianthus angustifolius – Swamp Sunflower *

Hemerocallis species – Daylily

Please see HGIC 1163, Daylily

Hibiscus coccineus – Texas Star *

Iris ensata – Japanese Iris *

Iris virginica – Blue Flag*

Iris laevigata – Japanese Water Iris*

Iris hybrids – Louisiana Iris *

Please see HGIC 1167, Iris

Ligularia species – Golden Ray *

Lobelia cardinalis – Cardinal Flower *

Lobelia siphilitica – Great Blue Lobelia *

Matteuccia pensylvanica – Ostrich Fern

Monarda species – Bee Balm

Myosotis sylvatica – Forget-me-not

Osmunda regalis – Royal Fern *

Please see HGIC 1176, Hardy Ferns

Physostegia virginiana – Obedient Plant

Primula species – Primrose

Tradescantia virginiana – Spiderwort

Zantedeschia aethiopeca – Calla *

Perennials for Hot, Dry Conditions

Achillea species – Yarrow

Agapanthus africanus – Lily-of-the-Nile

Agave parryi – Hardy Century Plant

Andropogon species – Bluestem Grass

Artemisia species – Artemesia

Asclepias tuberosa – Butterfly Weed

Baptisia species – False Indigo

Please see HGIC 1184, Baptisia

Belamcanda – Blackberry Lily

Coreopsis species – Coreopsis

Cortaderia selloana – Pampas Grass

Crocosmia x Curtonus ‘Lucifer’

Delosperma cooperi – Hardy Ice Plant

Festuca ovina – Blue Fescue

Gaillardia species – Blanket Flower

Gaura lindheimeri – Whirling Butterflies

Helianthus species – Perennial Sunflower

Hemerocallis species and hybrids – Daylily

Please see HGIC 1163, Daylily

Hesperaloe parviflora – False Red Yucca

Iris hybrids – Bearded Iris

Please see HGIC 1167, Iris

Kniphofia uvaria – Red Hot Poker

Lantana species – Lantana

Please see HGIC 1177, Lantana

Lavandula x intermedia – Provence Lavender

Liatris species – Gayfeather

Limonium latifolium – Sea Lavender

Nepeta species – Catmint

Oenothera species – Evening Primrose, Sundrops

Opuntia humifusa – Prickly Pear Cactus

Perovskia atriplicifolia – Russian Sage

Phlomis species – Jerusalem Sage

Phlox subulata – Thrift

Rudbeckia species – Black-eyed Susan

Ruellia brittoniana – Mexican Petunia

Salvia greggi – Texas Sage

Santolina species – Lavender Cotton

Sedum species – Stonecrop

Sempervivum tectorum – Hens & Chickens

Solidago odora – Sweet Goldenrod

Please see HGIC 2326 Goldenrod

Stachys byzantina – Lamb’s Ear

Verbena species – Verbena

Please see 1175, Verbena

Yucca species – Yucca

Perennials for Poor, Sandy Soil

Achillea species – Yarrow

Anthemis tinctoria – Golden Marguerite

Asclepias tuberosa – Butterfly Weed

Baptisia species – Wild Indigo

Please see HGIC 1184, Baptisia

Belamcanda chinensis – Blackberry Lily

Euphorbia species – Spurge

Gaillardia species – Blanket Flower

Gaura lindheimerii – Whirling Butterflies

Hemerocallis species – Daylily

Please see HGIC 1163, Daylily

Hesperaloe parviflora – False Red Yucca

Lantana species – Lantana

Please see HGIC 1177, Lantana

Plumbago auriculata – Plumbago

Please see HGIC 1180, Perennial Leadwort

Salvia greggi – Texas Sage

Setcrasea pallida – Purple Heart

Yucca species – Yucca

Attractive Foliage

Those marked with a * are gray or silvers that tolerate heat and humidity.

Acanthus species – Bear’s Breech

Alchemilla mollis – Lady’s Mantle

Artemisia ‘Powis Castle’ – Wormwood *

Baptisia species – False Indigo

Please see HGIC 1184, Baptisia

Chrysanthemum pacificum – Gold & Silver Mum

Cynara cardunculus – Cardoon

Delosperma cooperi – Hardy Ice Plant *

Dianthus gratianopolitanus – Cheddar Pink *

Helleborus x hybridus – Lenten Rose

Please see HGIC 1185, Lenten Rose

Heuchera species – Coral Bells

Hosta species and hybrids – Plantain Lily

Please see HGIC 1165, Hosta

Iris pallida ‘Variegata’ – Variegated Sweet Iris

Please see HGIC 1167, Iris

Lamium maculatum – Spotted Dead Nettle

Marrubium incanum – Silver Horehound *

Opuntia humifusa – Prickly Pear

Ornamental Grasses

Please see HGIC 1178, Ornamental Grasses

Phlomis fruticosa – Jerusalem Sage *

Polygonatum species – Solomon’s Seal

Pulmonaria species – Lungwort

Santolina chamaecyparissus – Lavender Cotton *

Sedum species – Stonecrop

Sempervivum tectorum – Hen-and-chicks

Stachys byzantina ‘Big Ears’ – Lamb’s Ear *

Teucrium fruticans – Silver Germander *

Perennials That Can Be Invasive

Aegopodium podagraria – Goutweed

Ajuga – Bugleweed

Please see HGIC 1102, Ajuga

Artemisia ludoviciana – Western Mugwort

Arundinaria species – Bamboo

Arundo donax – Giant Reed

Bambusa species – Clumping Bamboo

Please see HGIC 2320, Controlling Bamboo

Campanula rapunculoides – Creeping Bellflower

Chasmanthium latifolium – Upland River Oats

Chrysanthemum leucanthemum – Ox-eye Daisy

Coronilla varia – Crown Vetch

Cortaderia jubata – Purple Pampas Grass

Equisetum hyemale – Horsetail

Euphorbia cyparissias – Cypress Spurge

Elymus arenarius – Blue Lyme Grass

Eupatorium coelestinum – Hardy Ageratum

Hemerocallis fulva – Common Daylily, Ditch Lily

Imperata cylindrica – Japanese Blood Grass

Please see HGIC 2318, Cogongrass

Iris pseudocorus – Yellow Iris

Please see HGIC 1167, Iris

Lantana camara – Lantana

Please see HGIC 1177, Lantana

Lychnis coronaria – Rose Campion

Lysimachia species – Loosestrife

Lythrum salicaria – Purple Loosestrife

Miscanthus sinensis – Silver Grass, Zebra Grass

Please see HGIC 1178, Ornamental Grasses

Macleaya species – Plume Poppy

Mentha species – Mint

Oenothera species – Evening Primrose

Persicaria virginiana – Tovara

Phalaris arundinaceae var. picta – Ribbon Grass

Phyllostachys species – Japanese Bamboo

Please see HGIC 2320, Controlling Bamboo

Physostegia virginiana – Obedient Plant

Polygonum species – Knotweed

Tanacetum vulgare – Tansy

Vernonia species – Ironweed

Document last updated on  10/19 by Joey Williamson.

Originally published 06/99