Perennials - Growing
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Source: Clemson University, Home and Garden Center, Prepared by Karen Russ, HGIC Information Specialist, and Bob Polomski, Extension Consumer Horticulturist, Clemson University
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.
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.
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.
Soil Preparation
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.
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.
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.
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 Dividing Perennials, HGIC 1150. Many perennials are also easily propagated in this way. Other methods of propagating perennials include stem cuttings, root cuttings and seed.
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.
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 ShadeThose marked with a * will tolerate the most shade.
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Perennials for Hot, Dry Conditions
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Tolerant of Moist or Damp SoilsThose marked with a * will tolerate wetter soils.
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Perennials for Poor, Sandy Soil
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Attractive FoliageThose marked with a * are gray or silvers that tolerate heat and humidity.
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Perennials That Can Be Invasive
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