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Growing Perennials

HGIC 1153

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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 rebloom 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 or heavy shade, for dry 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.

Planting Perennials

Soil Preperation

Good soil preparation is extremely important for 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 pine bark humus, compost, leaf mold or small pea gravel to improve drainage and aeration. Improve water retention in sandy soils by mixing in 2 to 3 inches of pine bark humus, composted leaf mold or peat moss. 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 a complete fertilizer such as 10-10-10 at the rate of 1 pound per 100 square feet of bed area or a complete slow-release fertilizer following label directions.

A pH of 6.0 to 6.5 is ideal for most perennials. Most South Carolina soils are acidic and require the addition of lime to correct pH. Incorporate lime and fertilizer into the top 4 to 6 inches of soil after mixing in the soil amendments. Rake the soil surface smooth.

Planting

Most perennials can 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 plants 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 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 damging shallow roots. Read and follow label directions before using any herbicide.

Maintenance fertilization should be based on the results of a soil test. In the absence of a soil test, apply a complete fertilizer such as 8-8-8 or 10-10-10 at the rate of 1 to 2 pounds per 100 square feet of bed area just before new shoots emerge in the early spring. Avoid touching any emerging leaves with fertilizer to avoid leaf damage.

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.

Remove old flowers to encourage rebloom 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 Perennial. 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 susceptability 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 *
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
Chelone obliqua Turtlehead
Chrysogonum virginianum Green and 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)
Galium odoratum Sweet Woodruff *
Geranium maculatum Wild Cranesbill
Gillenia trifoliata Bowman’s Root
Helleborus foetidus Bearfoot Hellebore
Helleborus orientalis Lenten Rose
Heuchera species Coral Bells
Hosta species Plantain Lily
Iris cristata Crested 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 Wild Sweet William
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
Thalictrum species Meadow Rue
Tiarella speciesFoam 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 *
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
Filipendula species Meadow Sweet
Galium odoratum Sweet Woodruff
Helianthus angustifolius Swamp Sunflower *
Hemerocallis species Daylily
Hibiscus species Rose Mallow, Confederate Rose
Hibiscus coccineus Texas Star *
Iris ensata Japanese Iris *
Iris virginica Blue Flag*
Iris laevigata *
Iris hybrids Louisiana Iris *
Ligularia species Golden Ray *
Lobelia cardinalis Cardinal Flower *
Lobelia siphilitica Great BlueLobelia *
Matteuccia pensylvanica Ostrich Fern
Monarda species Bee Balm
Myosotis sylvatica Forget-me-not
Osmunda regalis Royal Fern *
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
Belamcanda Blackberry Lily
Coreopsis species Coreopsis
Cortaderia selloana Pampas Grass
Delosperma cooperi Hardy Ice Plant
Festuca ovina Blue Fescue
Gaillardia species Blanket Flower
Gaura lindheimeri Gaura
Helianthus species Perennial Sunflower
Hemerocallis species and hybridsDaylily
Hesperaloe parviflora False Red Yucca
Iris hybrids Bearded Iris
Kniphofia uvariaRed Hot Poker
Lantana species 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
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
Stachys byzantina Lamb’s Ear
Verbena species Verbena
Yucca speciesYucca

Perennials for Poor, Sandy Soil

Achillea species Yarrow
Anthemis tinctoria Golden Marguerite
Asclepias tuberosa Butterfly Weed
Baptisia species Wild Indigo
Belamcanda chinensis Blackberry Lily
Euphorbia species Spurge
Gaillardia species Blaket Flower
Gaura lindheimeriiGaura
Hemerocallis species Daylily
Hesperaloe parvifloraFalse Red Yucca
Lantana species Lantana
Plumbago auriculata Plumbago
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
Chrysanthemum pacificum Gold & Silver Mum
Cynara cardunculus Cardoon
Delosperma cooperi Hardy Ice Plant *
Dianthus gratianopolitanus Cheddar Pink *
Helleborus orientalis Lenten Rose
Heuchera species Coral Bells
Hosta species and hybrids Plantain Lily
Iris pallida ‘Variegata’ Varigated Sweet Iris
Lamium maculatum Spotted Dead Nettle
Marrubium incanum Silver Horehound *
Opuntia humifusa Prickly Pear
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
Artemisia ludoviciana Western Mugwort
Arundinaria speciesBamboo
Arundo donax Giant Reed
Bambusa species Clumping Bamboo
Campanula rapunculoides Creeping Bellflower
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
Houttuynia cordata Chameleon Plant
Imperata cylindrica Japanese Blood Grass
Iris pseudocorus Yellow Iris
Lantana camara Lantana
Lychnis coronaria Rose Campion
Lysimachia species Loosestrife
Lythrum salicaria Purple Loosestrife
Miscanthus sinensis Silver Grass; Zebra Grass
Macleaya species Plume Poppy
Mentha speciesMint
Oenothera species Evening Primrose
Persicaria virginiana Tovara
Phalaris arundinaceae var. picta Ribbon Grass
Phyllostachys species Japanese Bamboo
Physostegia virginiana Obedient Plant
Polygonum species Knotweed
Tanacetum vulgare Tansy
Vernonia species Ironweed

Prepared by Karen Russ, HGIC Horticulture Specialist, and Bob Polomski, Extension Consumer Horticulturist, Clemson University. (New 06/99.)

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